EX-4.2



 Exhibit 4.2 

BIOGEN INC., 
 as Issuer

 and 
 U.S. Bank
National Association, 
 as Trustee 

First Supplemental Indenture 

Dated as of September 15, 2015 







 TABLE OF CONTENTS 

 

							
	 	  	 	  	Page	 
		
	 ARTICLE I DEFINITIONS SECTION
	  	 	1	  
			
	 Section 1.1.
	  	 Certain Terms Defined in the Indenture
	  	 	2	  
			
	 Section 1.2.
	  	 Definitions
	  	 	2	  
		
	 ARTICLE II FORM AND TERMS OF THE NOTES
	  	 	5	  
			
	 Section 2.1.
	  	 Form and Dating
	  	 	5	  
			
	 Section 2.2.
	  	 Terms of the Notes
	  	 	7	  
			
	 Section 2.3.
	  	 Optional Redemption
	  	 	9	  
			
	 Section 2.4.
	  	 Repurchase of Notes Upon a Change of Control
	  	 	11	  
			
	 Section 2.5.
	  	 Limitation on Liens
	  	 	12	  
			
	 Section 2.6.
	  	 Limitation on Sale and Leaseback Transactions
	  	 	14	  
			
	 Section 2.7.
	  	 Exempted Liens and Sale and Leaseback Transactions
	  	 	14	  
		
	 ARTICLE III MISCELLANEOUS
	  	 	14	  
			
	 Section 3.1.
	  	 Trust Indenture Act Controls
	  	 	14	  
			
	 Section 3.2.
	  	 Governing Law
	  	 	15	  
			
	 Section 3.3.
	  	 Multiple Counterparts
	  	 	15	  
			
	 Section 3.4.
	  	 Severability
	  	 	15	  
			
	 Section 3.5.
	  	 Ratification
	  	 	15	  
			
	 Section 3.6.
	  	 Effectiveness
	  	 	15	  
		
	 EXHIBIT A Form of 2.900% Senior Note due 2020
	  	 	A-1	  
		
	 EXHIBIT B Form of 3.625% Senior Note due 2022
	  	 	B-1	  
		
	 EXHIBIT C Form of 4.050% Senior Note due 2025
	  	 	C-1	  
		
	 EXHIBIT D Form of 5.200% Senior Note due 2045
	  	 	D-1	  


  
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 FIRST SUPPLEMENTAL INDENTURE 

SUPPLEMENTAL INDENTURE (this “First Supplemental Indenture”), dated as of September 15, 2015, between BIOGEN INC., a Delaware
corporation (the “Company”), and U.S. Bank National Association, a national association, as Trustee (the “Trustee”). 

RECITALS OF THE COMPANY 

WHEREAS, the Company and the Trustee executed and delivered an Indenture, dated as of September 15, 2015 (the “Indenture”), to
provide for the issuance by the Company from time to time of Securities to be issued in one or more Series as provided in the Indenture; 

WHEREAS, the issuance and sale of $1,500,000,000 aggregate principal amount of a new Series of the Securities of the Company designated as its
2.900% Senior Notes due September 15, 2020 (the “Notes due 2020”), $1,000,000,000 aggregate principal amount of a new Series of the Securities of the Company designated as its 3.625% Senior Notes due September 15, 2022 (the
“Notes due 2022”), $1,750,000,000 aggregate principal amount of a new Series of the Securities of the Company designated as its 4.050% Senior Notes due September 15, 2025 (the “Notes due 2025”) and $1,750,000,000 aggregate
principal amount of a new Series of the Securities of the Company designated as its 5.200% Senior Notes due September 15, 2045 (the “Notes due 2045”, and together with the Notes due 2020, the Notes due 2022 and the Notes due 2025, the
“Notes”) have been authorized by resolutions adopted by the Board of Directors of the Company; 
 WHEREAS, the Company desires to
issue and sell $6,000,000,000 aggregate principal amount of the Notes on the date hereof; 
 WHEREAS, Sections 2.2 and 8.1 of the Indenture
provide that the Company, when authorized by a Board Resolution, and the Trustee may amend or supplement the Indenture to provide for the issuance of and to establish the form or terms and conditions of Securities of any Series as permitted by the
Indenture; 
 WHEREAS, the Company desires to establish the form, terms and conditions of the Notes; and 

WHEREAS, all things necessary to make this First Supplemental Indenture a valid supplement to the Indenture according to its terms and the
terms of the Indenture have been done; 
 NOW, THEREFORE, for and in consideration of the premises stated herein and the purchase of the
Notes by the Holders thereof, the parties hereto hereby enter into this First Supplemental Indenture, for the equal and proportionate benefit of all Holders of the Notes, as follows: 







 ARTICLE I 

DEFINITIONS SECTION 
 Section 1.1.
Certain Terms Defined in the Indenture. 
 For purposes of this First Supplemental Indenture, all capitalized terms used but not
defined herein shall have the meanings ascribed to such terms in the Indenture, as amended hereby. 
 Section 1.2. Definitions. 

For the benefit of the Holders of the Notes, Section 1.1 of the Indenture shall be amended by adding the following new definitions: 

“Attributable Debt” means, with respect to a Sale and Leaseback Transaction, an amount equal to the lesser of (1) the fair
market value of the Property (as determined in good faith by the Company’s board of directors); and (2) the present value of the total net amount of rent payments to be made under the lease during its remaining term, discounted at the rate
of interest set forth or implicit in the terms of the lease, compounded semi-annually. The calculation of the present value of the total net amount of rent payments is subject to adjustments specified in the indenture. 

“Change of Control” means the occurrence of any of the following: (1) the consummation of any transaction (including,
without limitation, any merger or consolidation) the result of which is that any “person” (as such term is used in Section 13(d) of the Exchange Act) (other than the Company or one of its Subsidiaries) becomes the beneficial
owner (as defined in Rules 13d-3 and 13d-5 under the Exchange Act), directly or indirectly, of more than 50% of the Voting Stock of the Company or other Voting Stock into which the Voting Stock of the Company is reclassified, consolidated, exchanged
or changed, measured by voting power rather than number of shares; provided, however, that a Person shall not be deemed beneficial owner of, or to own beneficially, (A) any Securities tendered pursuant to a tender or exchange offer made by or
on behalf of such Person or any of such Person’s Affiliates until such tendered Securities are accepted for purchase or exchange thereunder, or (B) any Securities if such beneficial ownership (i) arises solely as a result of a
revocable proxy delivered in response to a proxy or consent solicitation made pursuant to the applicable rules and regulations under the Exchange Act, and (ii) is not also then reportable on Schedule 13D (or any successor schedule) under
the Exchange Act; (2) the direct or indirect sale, transfer, conveyance or other disposition (other than by way of merger or consolidation), in one or more series of related transactions, of all or substantially all of the assets of the Company
and the assets of its Subsidiaries, taken as a whole, to one or more “persons” (as such term is used in Section 13(d) of the Exchange Act) (other than to the Company or one of its Subsidiaries) (a “Transferee”), provided,
however, that none of the circumstances in this clause (2) will be a Change of Control if the Persons that beneficially own the Company’s Voting Stock immediately prior to the transaction own, directly or indirectly, shares representing a
majority of the total Voting Stock as measured by voting power rather than number of shares of the Transferee; (3) the Company consolidates with, or merges with or into, any “person” (as such term is used in Section 13(d) of the
Exchange Act), or any such Person consolidates with, or merges with or into, the Company, in either case, pursuant to a transaction in which any of the Company’s outstanding Voting Stock or the Voting Stock of such other Person is converted
into or exchanged for cash, securities or other property, other than pursuant to a transaction in which shares of the Company’s Voting Stock outstanding 

  
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immediately prior to the transaction constitute, or are converted into or exchanged for, a majority of the Voting Stock of the surviving Person immediately after giving effect to such
transaction; or (4) the adoption of a plan relating to the Company’s liquidation or dissolution. 
 “Change of Control
Triggering Event” means the occurrence of both a Change of Control and a Rating Event. 
 “Comparable Treasury Issue” means
the United States Treasury security or securities selected by an Independent Investment Banker as having an actual or interpolated maturity comparable to the remaining term of the Notes of the applicable Series to be redeemed that would be utilized,
at the time of selection and in accordance with customary financial practice, in pricing new issues of corporate debt securities of a comparable maturity to the remaining term of such Notes. 

“Comparable Treasury Price” means, with respect to any Notes of a Series on any Redemption Date, (A) the average of the
Reference Treasury Dealer Quotations for such Redemption Date, after excluding the highest and lowest such Reference Treasury Dealer Quotations, or (B) if the Independent Investment Banker obtains fewer than four such Reference Treasury Dealer
Quotations, the average of all such quotations. 
 “Consolidated Total Assets” means, with respect to any Person as of any date,
the amount of total assets as shown on the consolidated balance sheet of such Person for the most recent fiscal quarter for which financial statements have been filed with the Securities and Exchange Commission, prepared in accordance with
accounting principles generally accepted in the United States. 
 “Global Notes” means, individually and collectively, each of the
Notes in the form of Global Securities issued to the Depositary or its nominee, substantially in the form of Exhibits A, B, C and D. 

“Hedging Obligations” means, with respect to any specified Person, the obligations of such Person under: 

(1) interest rate swap agreements (whether from fixed to floating or from floating to fixed), interest rate cap agreements and interest
rate collar agreements; 
 (2) other agreements or arrangements designed to manage interest rates or interest rate risk; and 

(3) other agreements or arrangements designed to protect such Person against fluctuations in currency exchange rates or commodity prices.

 “Independent Investment Banker” means one of the Reference Treasury Dealers appointed by the Company. 

“Investment Grade Rating” means a rating equal to or higher than Baa3 (or the equivalent) by Moody’s and BBB- (or the
equivalent) by S&P, and the equivalent investment grade credit rating from any additional rating agency or Rating Agencies selected by the Company. 

  
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 “Lien” means any pledge, mortgage, lien, encumbrance or other security interest. 

“Moody’s” means Moody’s Investors Service, Inc. or any successor thereto. 

“Property” means any property or asset, whether real, personal or mixed, or tangible or intangible. 

“Rating Agencies” means (1) each of Moody’s and S&P, and (2) if any of Moody’s and S&P ceases to rate
the Notes or fails to make a rating of the Notes publicly available for reasons outside of the control of the Company, a “nationally recognized statistical rating organization” within the meaning of Rule 15c3-1(c)(2)(vi)(F) under the
Exchange Act selected by the Company (as certified by a resolution of the Board of Directors of the Company) and which is reasonably acceptable to the Trustee as a replacement agency for Moody’s or S&P or both of them, as the case may be.

 “Rating Event” means (A) with respect to the Notes due 2020, the rating on such Notes is lowered by each of the Rating
Agencies and such Notes are rated below an Investment Grade Rating by each of the Rating Agencies, (B) with respect to the Notes due 2022, the rating on such Notes is lowered by each of the Rating Agencies and such Notes are rated below an
Investment Grade Rating by each of the Rating Agencies, (C) with respect to the Notes due 2025, the rating on such Notes is lowered by each of the Rating Agencies and such Notes are rated below an Investment Grade Rating by each of the Rating
Agencies, and (D) with respect to the Notes due 2045, the rating on such Notes is lowered by each of the Rating Agencies and such Notes are rated below an Investment Grade Rating by each of the Rating Agencies, in each case, on any day during
the period commencing on the earlier of the date of the first public notice of the occurrence of a Change of Control or the Company’s intention to effect a Change of Control and ending 60 days following consummation of such Change of Control
(which period will be extended so long as the rating of the applicable Series of Notes is under publicly announced consideration for a possible downgrade by any of the Rating Agencies). 

“Reference Treasury Dealer” means each of Goldman, Sachs & Co. and Merrill Lynch, Pierce, Fenner & Smith
Incorporated or their respective affiliates, which are primary U.S. Government securities dealers in The City of New York, and their respective successors plus three other primary U.S. Government securities dealers in The City of New York selected
by the Company; provided, however, that if any of the foregoing or their affiliates shall cease to be a primary U.S. Government securities dealer in The City of New York (a “Primary Treasury Dealer”), the Company will substitute therefor
another Primary Treasury Dealer. 
 “Reference Treasury Dealer Quotations” means, with respect to each Reference Treasury Dealer
and any Redemption Date, the average, as determined by the Independent Investment Banker, of the bid and asked prices for the applicable Comparable Treasury Issue (expressed in each case as a percentage of its principal amount) quoted in writing to
the Trustee by the Reference Treasury Dealers at 3:30 p.m. New York time on the third Business Day preceding such Redemption Date. 

  
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 “Sale and Leaseback Transaction” means any arrangement with any Person providing for
the leasing by the Company or any Subsidiary of the Company of any Property that has been or is to be sold or transferred by the Company or such Subsidiary, as the case may be, to such Person. 

“Subsidiary” of any Person means (1) a corporation, a majority of the outstanding voting stock of which is, at the time,
directly or indirectly, owned by such Person by one or more Subsidiaries of such Person, or by such Person and one or more Subsidiaries thereof or (2) any other Person (other than a corporation), including, without limitation, a partnership or
joint venture, in which such Person, one or more Subsidiaries thereof or such Person and one or more Subsidiaries thereof, directly or indirectly, at the date of determination thereof, has at least majority ownership interest entitled to vote in the
election of directors, managers or trustees thereof (or other Person performing similar functions). 
 “S&P” means
Standard & Poor’s Ratings Services, a Standard & Poor’s Financial Services LLC business, or any successor thereto. 

“Treasury Rate” means, with respect to any Redemption Date, the rate per annum equal to the semiannual equivalent yield to maturity
or interpolated (on a day count basis) of the Comparable Treasury Issue, assuming a price for the applicable Comparable Treasury Issue (expressed as a percentage of its principal amount) equal to the applicable Comparable Treasury Price for such
Redemption Date. 
 “Voting Stock” means, with respect to any specified “person” (as that term is used in
Section 13(d) of the Exchange Act) as of any date, the capital stock of such person that is at the time entitled to vote generally in the election of the board of directors of such person. 

ARTICLE II 
 FORM AND
TERMS OF THE NOTES 
 Section 2.1. Form and Dating. 

The Notes due 2020 and the Trustee’s certificate of authentication shall be substantially in the form of Exhibit A attached hereto.
The Notes due 2022 and the Trustee’s certificate of authentication shall be substantially in the form of Exhibit B attached hereto. The Notes due 2025 and the Trustee’s certificate of authentication shall be substantially in the
form of Exhibit C attached hereto. The Notes due 2045 and the Trustee’s certificate of authentication shall be substantially in the form of Exhibit D attached hereto. The Notes shall be executed on behalf of the Company by two
Officers of the Company or an Officer and an Assistant Secretary of the Company. The Company’s seal shall be impressed, affixed, imprinted or reproduced thereon. The Notes may have notations, legends or endorsements required by law, stock
exchange rules or usage. Each Note shall be dated the date of its authentication. The Notes and any beneficial interest in the Notes shall be in minimum denominations of $2,000 and integral multiples of $1,000 in excess thereof. 

The terms and notations contained in the Notes shall constitute, and are hereby expressly made, a part of the Indenture as supplemented by
this First Supplemental Indenture and the Company and the Trustee, by their execution and delivery of this First Supplemental Indenture, expressly agree to such terms and provisions and to be bound thereby. 

  
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 (a) Global Notes. The Notes of each Series designated herein shall be issued initially in
the form of one or more fully registered Global Securities, which shall be deposited on behalf of the purchasers of the Notes represented thereby with The Depository Trust Company, New York, New York (the “Depositary”) and registered in
the name of Cede & Co., the Depositary’s nominee, duly executed by the Company, authenticated by the Trustee and with guarantees endorsed thereon as hereinafter provided. The aggregate principal amount of outstanding Notes may from
time to time be increased or decreased by adjustments made on the records of the Trustee and the Depositary or its nominee as hereinafter provided. 

The Global Notes may not be transferred except by the Depositary, in whole and not in part, to another nominee of the Depositary or to a
successor of the Depositary or its nominee. If at any time the Depositary for the Notes notifies the Company that the Depositary is unwilling to continue as Depositary for the Global Notes or ceases to be a clearing agency, or if the Company so
elects or if there is an Event of Default under the Notes, then the Company shall execute, and the Trustee shall, upon receipt of a Company Order for authentication, authenticate and deliver, Definitive Notes in an aggregate principal amount equal
to the principal amount of the Global Notes in exchange for such Global Note, which the Depositary will distribute to its participants. 

(b) Book-Entry Provisions. This Section 2.1(b) shall apply only to the Global Notes deposited with or on behalf of the Depositary.

 The Company shall execute and the Trustee shall, in accordance with this Section 2.1(b), authenticate and deliver the Global Notes
that shall be registered in the name of the Depositary or the nominee of the Depositary and shall be delivered by the Trustee to the Depositary or pursuant to the Depositary’s instructions. 

Depositary participants shall have no rights either under the Indenture or with respect to any Global Notes held on their behalf by the
Depositary or under such Global Notes. The Depositary shall be treated by the Company, the Trustee and any agent of the Company or the Trustee as the absolute owner of such Global Note for all purposes under the Indenture. Notwithstanding the
foregoing, nothing herein shall prevent the Company or the Trustee from giving effect to any written certification, proxy or other authorization furnished by the Depositary or impair, as between the Depositary and the Depository participants, the
operation of customary practices of such Depositary governing the exercise of the rights of an owner of a beneficial interest in the Global Notes. 

(c) Definitive Notes. Notes issued in certificated form shall be substantially in the form of Exhibit A, Exhibit B, Exhibit C or
Exhibit D, as applicable, attached hereto, but without including the text referred to therein as applying only to Global Notes. Except as provided above in subsection (a), owners of beneficial interests in the Global Notes will not be entitled to
receive physical delivery of certificated Notes. 

  
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 (d) Transfer and Exchange of the Notes. The transfer and exchange of beneficial interests
in the Global Notes shall be effected through the Depositary, in accordance with the Indenture and the procedures of the Depositary therefor. Beneficial interests in the Global Notes may be transferred to Persons who take delivery thereof in the
form of a beneficial interest in the Global Notes. 
 (e) Paying Agent. The Company appoints the Trustee as the initial agent of the
Company for the payment of the principal of (and premium, if any) and interest on the Notes and the Corporate Trust Office of the Trustee in the City of St. Paul, Minnesota, be and hereby is, designated as the office or agency where the Notes may be
presented for payment and where notices to or demands upon the Company in respect of the Notes and the Indenture pursuant to which the Notes are to be issued may be served. 

Section 2.2. Terms of the Notes. 

The following terms relating to the Notes are hereby established: 

(a) Title. The Notes due 2020 shall constitute a Series of Securities having the title “2.900% Senior Notes due 2020”, the
Notes due 2022 shall constitute a separate Series of Securities having the title “3.625% Senior Notes due 2022”, the Notes due 2025 shall constitute a separate Series of Securities having the title “4.050% Senior Notes due 2025”
and the Notes due 2045 shall constitute a separate Series of Securities having the title “5.200% Senior Notes due 2045”. 
 (b)
Principal Amount. The aggregate principal amount of the Notes due 2020 that may be initially authenticated and delivered under the Indenture (except for Notes due 2020 authenticated and delivered upon registration of, transfer of, or in
exchange for, or in lieu of, other Notes due 2020 pursuant to Sections 2.7, 2.8, 2.11, 3.6 or 8.5 of the Indenture) shall be $1,500,000,000. The aggregate principal amount of the Notes due 2022 that may be initially authenticated and delivered under
the Indenture (except for Notes due 2022 authenticated and delivered upon registration of, transfer of, or in exchange for, or in lieu of, other Notes due 2022 pursuant to Sections 2.7, 2.8, 2.11, 3.6 or 8.5 of the Indenture) shall be
$1,000,000,000. The aggregate principal amount of the Notes due 2025 that may be initially authenticated and delivered under the Indenture (except for Notes due 2025 authenticated and delivered upon registration of, transfer of, or in exchange for,
or in lieu of, other Notes due 2025 pursuant to Sections 2.7, 2.8, 2.11, 3.6 or 8.5 of the Indenture) shall be $1,750,000,000. The aggregate principal amount of the Notes due 2045 that may be initially authenticated and delivered under the Indenture
(except for Notes due 2045 authenticated and delivered upon registration of, transfer of, or in exchange for, or in lieu of, other Notes due 2045 pursuant to Sections 2.7, 2.8, 2.11, 3.6 or 8.5 of the Indenture) shall be $1,750,000,000. The Company
may from time to time, without the consent of the Holders of Notes of any Series, issue additional Notes (in any such case “Additional Notes”) of any Series having the same ranking and the same interest rate, maturity and other terms as
the Notes of that Series. Any additional Notes of a Series and the existing Notes of that Series will constitute a single Series under the Indenture and all references to the relevant Notes shall include the Additional Notes unless the context
otherwise requires; provided, that if the Additional Notes of any Series are not fungible with the Notes of such Series for U.S. federal income tax purposes, the Additional Notes will have a separate CUSIP number. 

  
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 (c) Issuance Price. The Notes due 2020 shall be issued at a price to the public of 99.792%
of the principal amount of such Series, the Notes due 2022 shall be issued at a price to the public of 99.920% of the principal amount of such Series, the Notes due 2025 shall be issued at a price to the public of 99.764% of the principal amount of
such Series and the Notes due 2045 shall be issued at a price to the public of 99.294% of the principal amount of such Series, plus, in each case, accrued interest, if any, from September 15, 2015 to the Original Issue Date (as defined in the
Note of the applicable Series). 
 (d) Maturity Date. The entire outstanding principal of the Notes due 2020 shall be payable on
September 15, 2020, the entire outstanding principal of the Notes due 2022 shall be payable on September 15, 2022, the entire outstanding principal of the Notes due 2025 shall be payable on September 15, 2025 and the entire
outstanding principal of the Notes due 2045 shall be payable on September 15, 2045. 
 (e) Interest Rate; Place and Method of
Payment. The rate at which the Notes due 2020 shall bear interest shall be 2.900% per annum, the rate at which the Notes due 2022 shall bear interest shall be 3.625% per annum, the rate at which the Notes due 2025 shall bear interest
shall be 4.050% per annum and the rate at which the Notes due 2045 shall bear interest shall be 5.200% per annum; the date from which interest shall accrue on the Notes shall be September 15, 2015, or the most recent Interest Payment
Date to which interest has been paid or provided for; the Interest Payment Dates for the Notes shall be March 15 and September 15 of each year, beginning March 15, 2016; the interest so payable, and punctually paid or duly provided
for, on any Interest Payment Date, will be paid, in immediately available funds, to the Persons in whose names the Notes (or one or more predecessor Securities) is registered at the close of business on the Regular Record Date for such interest,
which shall be March 1 or September 1, as the case may be, next preceding such Interest Payment Date. Any such interest not punctually paid or duly provided for shall forthwith cease to be payable to the respective Holders on such Regular
Record Date, and such defaulted interest, may be paid to the Persons in whose names the Notes (or one or more predecessor Securities) is registered at the close of business on a special record date for the payment of such defaulted interest to be
fixed by the Trustee, notice whereof shall be given to Holders of Notes not less than 15 days prior to such special record date, or may be paid at any time in any other lawful manner not inconsistent with requirements of any securities exchange on
which the Notes may be listed, and upon such notice as may be required by such exchange, all as more fully provided in said Indenture. Payment of principal and interest on this Note will be made at the Corporate Trust Office of the Trustee or such
other office or agency of the Company as may be designated for such purpose, in such coin or currency of the United States of America as at the time of payment is legal tender for payment of public and private debts; provided, however,
that each installment of interest and principal on the Notes may at the Company’s option be paid in immediately available funds by transfer to an account maintained by the payee located in the United States. 

(f) Optional Redemption. The Notes of each Series are redeemable at the option of the Company on the terms and conditions described in
Section 2.3 hereof. 
 (g) Sinking Fund Obligation. There is no sinking fund obligation. 

  
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 (h) Mandatory Redemption or Repurchase. The Company shall be required to make an offer to
repurchase the Notes of any Series upon the occurrence of a Change of Control Triggering Event on the terms and conditions described in Section 2.4 hereof. 

(i) Form and Denomination of Notes. The Notes of each Series shall be issued in registered form in the denominations specified in
Section 2.1 hereof. 
 (j) Principal Payable Upon Acceleration. The entire principal amount of, and premium, if any, on all the
Notes of any Series then outstanding is payable upon acceleration of such Notes in accordance with Section 6.2 of the Indenture. 
 (k)
Currency. The currency of denomination of the Notes is United States Dollars. Payment of principal of and interest and premium, if any, on the Notes will be made in United States Dollars. 

(l) Payment Not Made by Reference to Index. Payments of principal of or interest or premium, if any, on the Notes of any Series shall
not be determined by reference to any index. 
 (m) Notes Unsecured. Except as otherwise required pursuant to Section 2.5
hereof, the Notes are not secured by any collateral. 
 (n) Additional/Different Covenants. In addition to the covenants set forth in
Indenture, the Company shall be subject to the obligations set forth in Sections 2.3, 2.4, 2.5, 2.6 and 2.7 hereof. 
 (o) Modification
to Events of Default. There is no addition to, deletion of or change in (i) any Events of Default as applicable to the Notes of any Series as set forth under the Indenture or (ii) the right of the Trustee or the requisite Holders of
any Series of Notes to declare the principal amount thereof due and payable pursuant to Section 6.2 of the Indenture. 
 (p)
Conversion. No Notes of any Series are convertible or exchangeable for shares of common stock or preferred stock of the Company. 

(q) Depositories and Agents. The Notes of each Series shall be deposited with the The Depository Trust Company, acting as Depositary,
as described in Section 2.1(a) hereof. The Company appoints the Trustee as initial paying agent for the Notes as described in Section 2.1(e) hereof. There is no interest rate calculation agent, exchange rate calculation agent or other
agent with respect to the Notes of any Series other than those appointed herein. 
 (r) Subordination. The Notes are not subordinated
in right of payment to any other unsecured Indebtedness of the Company. 
 (s) Defeasance. The Notes of any Series are defeasible
pursuant to Article 9 of the Indenture. 
 Section 2.3. Optional Redemption. 

(a) The provisions of Article 3 of the Indenture shall apply to the Notes. 

  
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 (b) (i) At any time and from time to time, the Notes due 2020 will be redeemable, as a whole or
in part, at the Company’s option, on at least 30 days, but not more than 60 days, prior notice mailed to the registered address of each holder of the Notes due 2020, at a redemption price equal to the greater of (x) 100% of principal
amount of the Notes to be redeemed, or (y) the sum of the present values of the remaining scheduled payments of interest and principal thereon (exclusive of interest accrued and unpaid to, but not including, the date of redemption) discounted
to the date of redemption on a semiannual basis, assuming a 360-day year consisting of twelve 30-day months, at the Treasury Rate plus 20 basis points, plus, in either case, accrued and unpaid interest to, but not including, the date of redemption.

 (ii) At any time and from time to time, the Notes due 2022 will be redeemable, as a whole or in part, at the Company’s option, on at
least 30 days, but not more than 60 days, prior notice mailed to the registered address of each holder of the Notes due 2022, at a redemption price equal to the greater of (x) 100% of principal amount of the Notes to be redeemed, or
(y) the sum of the present values of the remaining scheduled payments of interest and principal thereon (exclusive of interest accrued and unpaid to, but not including, the date of redemption) discounted to the date of redemption on a
semiannual basis, assuming a 360-day year consisting of twelve 30-day months, at the Treasury Rate plus 25 basis points, plus, in either case, accrued and unpaid interest to, but not including, the date of redemption. 

(iii) At any time and from time to time and from time to time prior to June 15, 2025 (the date that is three months prior to maturity),
the Notes due 2025 will be redeemable, as a whole or in part, at the Company’s option, on at least 30 days, but not more than 60 days, prior notice mailed to the registered address of each holder of the Notes due 2025, at a redemption price
equal to the greater of (x) 100% of principal amount of the Notes to be redeemed, or (y) the sum of the present values of the remaining scheduled payments of interest and principal thereon (exclusive of interest accrued and unpaid to, but
not including, the date of redemption) discounted to the date of redemption on a semiannual basis, assuming a 360-day year consisting of twelve 30-day months, at the Treasury Rate plus 30 basis points, plus, in either case, accrued and unpaid
interest to, but not including, the date of redemption. On or after June 15, 2025 (the date that is three months before maturity), the Notes due 2025 may be redeemed, as a whole or in part, at the Company’s option, on at least 30 days, but
not more than 60 days, prior notice mailed to the registered address of each Holder of the Notes due 2025, at a redemption price equal to 100% of the principal amount of the Notes due 2025to be redeemed on the redemption date plus accrued and unpaid
interest to, but not including, the Redemption Date. 
 (iv) At any time and from time to time and from time to time prior to March 15,
2045 (the date that is six months prior to maturity), the Notes due 2045 will be redeemable, as a whole or in part, at the Company’s option, on at least 30 days, but not more than 60 days, prior notice mailed to the registered address of each
holder of the Notes due 2045, at a redemption price equal to the greater of (x) 100% of principal amount of the Notes to be redeemed, or (y) the sum of the present values of the remaining scheduled payments of interest and principal
thereon (exclusive of interest accrued and unpaid to, but not including, the date of redemption) discounted to the date of redemption on a semiannual basis, assuming a 360-day year consisting of twelve 30-day months, at the Treasury Rate


  
 -10- 








 
plus 35 basis points, plus, in either case, accrued and unpaid interest to, but not including, the date of redemption. On or after March 15, 2045 (the date that is six months before
maturity), the Notes due 2045 may be redeemed, as a whole or in part, at the Company’s option, on at least 30 days, but not more than 60 days, prior notice mailed to the registered address of each Holder of the Notes due 2045, at a redemption
price equal to 100% of the principal amount of the Notes due 2045 to be redeemed on the redemption date plus accrued and unpaid interest to, but not including, the Redemption Date. 

(c) On and after the Redemption Date for the Notes of any Series, interest will cease to accrue on the Notes of such Series or any portion
thereof called for redemption, unless the Company defaults in the payment of the redemption price. On or before the Redemption Date for the Notes of such Series, the Company will deposit with a Paying Agent, or the Trustee, funds sufficient to pay
the redemption price of the Notes to be redeemed on such date. If less than all of the Notes of a Series are to be redeemed, the Notes of that Series to be redeemed will be selected by DTC in accordance with its standard procedures. If the Notes to
be redeemed are not global notes then held by DTC, or DTC prescribes no method of selection, the Trustee will select the Notes to be redeemed on a pro rata basis, by lot, or by any other method the Trustee deems fair and appropriate and subject to
and otherwise in accordance with the procedures of DTC. 
 Section 2.4. Repurchase of Notes Upon a Change of Control. 

(a) If a Change of Control Triggering Event occurs with respect to the Notes of a Series, unless the Company shall have exercised its option to
redeem the Notes of such Series as described in Section 2.3 of this First Supplemental Indenture, the Company shall be required to make an offer (the “Change of Control Offer”) to each holder of the Notes of such Series to repurchase
all or any part (equal to $2,000 or an integral multiple of $1,000 in excess thereof) of such Holder’s Notes of such Series on the terms set forth in this Section 2.4 and in the Notes. In the Change of Control Offer, the Company shall
offer payment in cash equal to 101% of the aggregate principal amount of Notes repurchased, plus accrued and unpaid interest, if any, on the Notes repurchased to but not including the date of repurchase (the “Change of Control Payment”).
With respect to the Notes of each Series, within 30 days following any Change of Control Triggering Event or, at the option of the Company, prior to any Change of Control, but after public announcement of the transaction that constitutes or may
constitute the Change of Control, the Company shall mail a notice to Holders of Notes of the applicable Series describing the transaction that constitutes or may constitute the Change of Control Triggering Event and offering to repurchase the Notes
of such Series on the date specified in the notice, which date shall be no earlier than 30 days and no later than 60 days from the date such notice is mailed or, if the notice is mailed prior to the Change of Control, no earlier than 30 days and no
later than 60 days from the date on which the Change of Control Triggering Event occurs (the “Change of Control Payment Date”). The notice shall, if mailed prior to the date of consummation of the Change of Control, state that the offer to
purchase is conditioned on the Change of Control Triggering Event occurring on or prior to the Change of Control Payment Date. 
 (b) On the
Change of Control Payment Date, the Company shall, to the extent lawful: 
 (1) accept for payment all Notes or portions of Notes properly
tendered pursuant to the Change of Control Offer; 

  
 -11- 








 (2) deposit with the Paying Agent an amount equal to the Change of Control Payment in respect of
all Notes or portions of Notes properly tendered; and 
 (3) deliver or cause to be delivered to the Trustee the Notes properly accepted
together with an Officers’ Certificate stating the aggregate principal amount of Notes or portions of Notes being repurchased. 
 (c)
The Company shall not be required to make a Change of Control Offer upon the occurrence of a Change of Control Triggering Event if a third party makes such an offer in the manner, at the times and otherwise in compliance with the requirements for an
offer made by the Company and the third party repurchases all Notes properly tendered and not withdrawn under its offer. In addition, the Company shall not repurchase any Notes if there has occurred and is continuing on the Change of Control Payment
Date an Event of Default under the Indenture, other than an Event of Default arising as a result of a default in the payment of the Change of Control Payment upon a Change of Control Triggering Event. 

(d) The Company shall comply in all material respects with the requirements of Rule 14e-1 under the Exchange Act and any other securities laws
and regulations thereunder to the extent such laws and regulations are applicable in connection with the repurchase of the Notes as a result of a Change of Control Triggering Event. To the extent that the provisions of any such securities laws or
regulations conflict with the Change of Control Offer provisions of the Notes, the Company shall comply with the applicable securities laws and regulations and shall not be deemed to have breached its obligations under the Change of Control Offer
provisions of the Notes by virtue of any such conflict. 
 Section 2.5. Limitation on Liens. 

For the benefit of the Holders of the Notes, a new Section 4.7 shall be added to the Indenture as follows: 

“Other than as provided in Section 4.9, the Company shall not, and shall not permit any Subsidiaries of the Company to, create or
assume any Indebtedness secured by any Lien on any of the Company’s or such Subsidiary’s respective Properties unless the Notes are secured by such Lien equally and ratably with, or prior to, the Indebtedness secured by such Lien. This
restriction does not apply to Indebtedness that is secured by (i) Liens existing on the date of the issuance of the Notes; (ii) Liens securing only the Notes; (iii) Liens on Property or shares of stock in respect of Indebtedness of a
Person existing at the time such Person becomes a Subsidiary of the Company or is merged into or consolidated with, or its assets are acquired by, the Company or any Subsidiary of the Company (provided that such Lien was not incurred in
anticipation of such transaction and was in existence prior to such transaction) so long as such Lien does not extend to any other Property and the Indebtedness so secured is not increased; (iv) Liens to secure Indebtedness incurred for the
purpose of all or any part of a Property’s purchase price or cost of construction or additions, repairs, alterations, or other improvements; provided that (1) the principal amount of any Indebtedness secured by such Lien does not
exceed 100% of such Property’s purchase price or cost, (2) such Lien does not extend to or cover any other Property other than the Property so purchased, constructed or on which such additions, repairs, alterations or other improvements
were so made, and (3) such Lien is incurred prior to or within 

  
 -12- 








 
270 days after the acquisition of such Property or the completion of construction or such additions, repairs, alterations or other improvements and the full operation of such Property thereafter;
(v) Liens in favor of the United States or any state thereof, or any instrumentality of either, to secure certain payments pursuant to any contract or statute; (vi) Liens for taxes or assessments or other governmental charges or levies
which are not overdue for a period exceeding 60 days unless such Liens are being contested in good faith and for which adequate reserves are being maintained, to the extent required by generally accepted accounting principles; (vii) title
exceptions, easements, licenses, leases and other similar Liens that are not consensual and that do not materially impair the use of the Property subject thereto; (viii) Liens to secure obligations under worker’s compensation laws,
unemployment compensation, old-age pensions and other social security benefits or similar legislation; (ix) Liens arising out of legal proceedings, including Liens arising out of judgments or awards; (x) warehousemen’s,
materialmen’s, carrier’s, landlord’s and other similar Liens for sums not overdue for a period exceeding 60 days unless such Liens are being contested in good faith and for which adequate reserves are being maintained, to the extent
required by generally accepted accounting principles; (xi) Liens incurred to secure the performance of statutory obligations, surety or appeal bonds, performance or return-of-money bonds, insurance, self-insurance or other obligations of a like
nature incurred in the ordinary course of business; (xii) Liens that are rights of set-off relating to the establishment of depository relations with banks not given in connection with the issuance of Indebtedness; (xiii) Liens on the
assets of a special purpose Subsidiary resulting from securitization transactions with respect to accounts receivable, royalties and similar assets included in such securitization transactions; (xiv) Liens upon specific items of inventory or
other goods and proceeds of any Person securing such Person’s obligations in respect of bankers’ acceptances issued or created for the account of such Person to facilitate the purchase, shipment or storage of such inventory or other goods;
(xv) Liens securing reimbursement obligations with respect to letters of credit that encumber documents and other Property relating to such letters of credit and the products and proceeds thereof; (xvi) Liens on key-man life insurance
policies granted to secure Indebtedness of the Company against the cash surrender value thereof; (xvii) Liens encumbering customary initial deposits and margin deposits and other Liens in the ordinary course of business, in each case securing
Hedging Obligations and forward contract, option, futures contracts, futures options or similar agreements or arrangements designed to protect the Company or any of its Subsidiaries from fluctuations in interest rates, currencies or the price of
commodities; (xviii) Liens arising out of conditional sale, title retention, consignment or similar arrangements for the sale of goods entered into by the Company or any of its Subsidiaries in the ordinary course of business; (xix) Liens
in favor of the Company or the favor of any of its Subsidiaries; or (xx) Liens to secure any extension, renewal, refinancing or refunding (or successive extensions, renewals, refinancings or refundings), in whole or in part, of any Indebtedness
secured by Liens referred to in clauses (i) to (xx) or Liens created in connection with any amendment, consent or waiver relating to such Indebtedness, so long as such Lien does not extend to any other Property and the Indebtedness so
secured does not exceed the fair market value (as determined by the Company’s board of directors) of the assets subject to such Liens at the time of such extension, renewal, refinancing or refunding, or such amendment, consent or waiver, as the
case may be.” 

  
 -13- 








 Section 2.6. Limitation on Sale and Leaseback Transactions. 

For the benefit of the Holders of the Notes a new Section 4.8 shall be added to the Indenture as follows: 

“Other than as provided under Section 4.9, the Company shall not, and shall not permit any of its Subsidiaries to, enter into any
Sale and Leaseback Transaction with respect to any of the Company’s or such Subsidiary’s respective Properties, the acquisition or completion of construction and commencement of full operations of which has occurred more than 270 days
prior thereto, unless (i) such transaction is entered into prior to the first issue date of the Notes; (ii) such transaction is for the sale and leasing back to the Company of any Property by one of its Subsidiaries; (iii) the Company
or such Subsidiary is entitled to incur Indebtedness secured by a mortgage on the Property to be leased in an amount equal to the Attributable Debt with respect to such Sale and Leaseback Transaction without equally and ratably securing the Notes
pursuant to the first sentence of Section 4.7; (iv) the lease is for a period not in excess of five years, including renewal rights; or (v) the Company or the Subsidiary, prior to or within 270 days after the sale of such Property in
connection with the Sale and Leaseback Transaction is completed, applies the net cash proceeds of the sale of the Property leased to (1) the retirement of the Notes or debt of the Company ranking equally with the Notes or to the retirement of
any debt of a Subsidiary of the Company, or (2) the acquisition of different property, facilities or equipment or the expansion of the Company’s existing business, including the acquisition of other businesses.” 

Section 2.7. Exempted Liens and Sale and Leaseback Transactions. 

For the benefit of the Holders of the Notes a new Section 4.9 shall be added to the Indenture as follows: 

“Notwithstanding the restrictions described under Sections 4.7 or 4.8, the Company or any Subsidiary of the Company may create or assume
any Liens or enter into any Sale and Leaseback Transactions not otherwise permitted as described above, if the sum of the following does not exceed 10% of Consolidated Total Assets (i) the outstanding Indebtedness secured by such Liens (not
including any Liens permitted under Section 4.7 which amount does not include any Liens permitted under the provisions of this Section 4.9); plus (ii) all Attributable Debt in respect of such Sale and Leaseback Transaction entered
into (not including any Sale and Leaseback Transactions permitted under Section 4.8 which amount does not include any Sale and Leaseback Transactions permitted under the provisions of this Section 4.9), measured, in each case, at the time
such Lien is incurred or any such Sale and Leaseback Transaction is entered into by the Company or such Subsidiary of the Company.” 

ARTICLE III 

MISCELLANEOUS 
 Section 3.1. Trust
Indenture Act Controls. 
 If any provision of this First Supplemental Indenture limits, qualifies or conflicts with another provision
which is required to be included in this First Supplemental Indenture by the TIA, the required provision shall control. If any provision of this First Supplemental Indenture modifies or excludes any provision of the TIA which may be so modified or
excluded, the latter provision shall be deemed to apply to this First Supplemental Indenture as so modified or to be excluded, as the case may be. 

  
 -14- 








 Section 3.2. Governing Law. 

This First Supplemental Indenture and the Notes shall be governed by and construed in accordance with the laws of the State of New York. 

Section 3.3. Multiple Counterparts. 

The parties may sign multiple counterparts of this First Supplemental Indenture. Each signed counterpart shall be deemed an original, but all
of them together represent one and the same First Supplemental Indenture. 
 Section 3.4. Severability. 

Each provision of this First Supplemental Indenture shall be considered separable and if for any reason any provision which is not essential to
the effectuation of the basic purpose of this First Supplemental Indenture or the Notes shall be invalid, illegal or unenforceable, the validity, legality and enforceability of the remaining provisions shall not in any way be affected or impaired
thereby and a Holder shall have no claim therefor against any party hereto. 
 Section 3.5. Ratification. 

The Indenture, as supplemented and amended by this First Supplemental Indenture, is in all respects ratified and confirmed. The Indenture and
this First Supplemental Indenture shall be read, taken and construed as one and the same instrument. All provisions included in this First Supplemental Indenture supersede any conflicting provisions included in the Indenture unless not permitted by
law. The Trustee accepts the trusts created by the Indenture, as supplemented by this First Supplemental Indenture, and agrees to perform the same upon the terms and conditions of the Indenture, as supplemented by this First Supplemental Indenture.

 Section 3.6. Effectiveness. 

The provisions of this First Supplemental Indenture shall become effective as of the date hereof. 

[Remainder of page intentionally left blank.] 

  
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 IN WITNESS WHEREOF, the parties hereto have caused this First Supplemental Indenture to be duly
executed as of the date first above written. 
  

			
	BIOGEN INC.
		
	By:	 	 /s/ Michael Dambach

	Name:	 	Michael Dambach
	Title:	 	Vice President, Treasurer
	
	U.S. BANK NATIONAL ASSOCIATION, as Trustee
		
	By:	 	 /s/ Laura Cawley

	Name:	 	Laura Cawley
	Title:	 	Vice President









 EXHIBIT A 

FORM OF 2.900% SENIOR NOTE DUE 2020 

THIS NOTE IS A GLOBAL SECURITY WITHIN THE MEANING OF THE INDENTURE HEREINAFTER REFERRED TO AND IS REGISTERED IN THE NAME OF THE DEPOSITARY OR
A NOMINEE OF THE DEPOSITARY. THIS NOTE IS EXCHANGEABLE FOR NOTES REGISTERED IN THE NAME OF A PERSON OTHER THAN THE DEPOSITARY OR ITS NOMINEE ONLY IN THE LIMITED CIRCUMSTANCES DESCRIBED IN THE INDENTURE, AND MAY NOT BE TRANSFERRED EXCEPT AS A WHOLE
BY THE DEPOSITARY TO A NOMINEE OF THE DEPOSITARY, BY A NOMINEE OF THE DEPOSITARY TO THE DEPOSITARY OR ANOTHER NOMINEE OF THE DEPOSITARY OR BY THE DEPOSITARY OR ANY SUCH NOMINEE TO A SUCCESSOR DEPOSITARY OR A NOMINEE OF SUCH A SUCCESSOR DEPOSITARY.

 UNLESS THIS GLOBAL SECURITY IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION
(“DTC”), TO THE ISSUER OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY GLOBAL SECURITY ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR IN SUCH OTHER NAME AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF
DTC (AND ANY PAYMENT IS MADE TO CEDE & CO. OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE
REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN. 
 BIOGEN INC. 

2.900% Senior Note due 2020 
  

			
	REGISTERED	 	PRINCIPAL AMOUNT
	No.	 	$

 CUSIP: 
 ISIN: 

Biogen Inc., a Delaware corporation (herein called the “Company,” which term includes any successor Person under the Indenture
hereinafter referred to), for value received, hereby promises to pay to Cede & Co., or registered assigns, the principal sum of $         on September 15, 2020 (the “Maturity Date”)
(except to the extent redeemed or repaid prior to the Maturity Date) and to pay interest thereon from September 15, 2015 (the “Original Issue Date”) or from the most recent Interest Payment Date to which interest has been paid or duly
provided for semi-annually at the rate of 2.900% per annum, on March 15 and September 15 (each such date, an “Interest Payment Date”), commencing March 15, 2016, until the principal hereof is paid or made available for
payment. 

  
 A-1 








 Payment of Interest. The interest so payable, and punctually paid or made available for
payment, on any Interest Payment Date, will, as provided in the Indenture, be paid, in immediately available funds, to the Person in whose name this Note (or one or more Predecessor Securities) is registered at the close of business on
September 1 or March 1 (whether or not a Business Day, as defined in the Indenture), as the case may be, next preceding such Interest Payment Date (the “Regular Record Date”). Any such interest not punctually paid or duly
provided for (“Defaulted Interest”) will forthwith cease to be payable to the Holder on such Regular Record Date, and such Defaulted Interest, may be paid to the Person in whose name this Note (or one or more Predecessor Securities) is
registered at the close of business on a special record date (the “Special Record Date”) for the payment of such Defaulted Interest to be fixed by the Trustee, notice whereof shall be given to Holders of Notes not less than fifteen days
prior to such Special Record Date, or may be paid at any time in any other lawful manner not inconsistent with requirements of any securities exchange on which the Notes may be listed, and upon such notice as may be required by such exchange, all as
more fully provided in said Indenture. 
 Place of Payment. Payment of principal, premium, if any, and interest on this Note will be
made at the Corporate Trust Office of the Trustee or such other office or agency of the Company as may be designated for such purpose, in such coin or currency of the United States of America as at the time of payment is legal tender for payment of
public and private debts; provided, however, that each installment of interest, premium, if any, and principal on this Note may at the Company’s option be paid in immediately available funds by transfer to an account maintained by
the payee located in the United States. 
 Time of Payment. In any case where any Interest Payment Date, the Maturity Date or any
date fixed for redemption or repayment of the Notes shall not be a Business Day, then (notwithstanding any other provision of the Indenture or this Note), payment of principal or interest, if any, need not be made on such date, but may be made on
the next succeeding Business Day with the same force and effect as if made on such Interest Payment Date, the Maturity Date or the date so fixed for redemption or repayment, and no interest shall accrue in respect of the delay. 

General. This Note is one of a duly authorized issue of Securities of the Company, issued and to be issued in one or more Series under
an indenture (the “Base Indenture”), dated as of September 15, 2015, between the Company and U.S. Bank National Association (herein called the “Trustee,” which term includes any successor trustee under the Indenture with
respect to a Series of which this Note is a part), as supplemented by a First Supplemental Indenture thereto, dated as of September 15, 2015 (the “First Supplemental Indenture” and, together with the Base Indenture, the
“Indenture”). Reference is hereby made to the Indenture for a statement of the respective rights, limitations of rights, duties and immunities thereunder of the Company, the Trustee and the Holders of the Securities, and of the terms upon
which the Securities are, and are to be, authenticated and delivered. This Note is one of a duly authorized Series of Securities designated as “2.900% Senior Notes due 2020” (collectively, the “Notes”), initially limited in
aggregate principal amount to $        . 

  
 A-2 








 Further Issuance. The Company may from time to time, without the consent of the Holders of
the Notes, issue additional Securities (the “Additional Securities”) of this Series having the same ranking and the same interest rate, maturity and other terms as the Notes. Any Additional Securities of this Series and the Notes will
constitute a single Series under the Indenture and all references to the Notes shall include the Additional Securities unless the context otherwise requires. 

Events of Default. If an Event of Default with respect to the Notes shall have occurred and be continuing, the principal of the Notes
may be declared due and payable in the manner and with the effect provided in the Indenture. 
 Sinking Fund. The Notes are not
subject to any sinking fund. 
 Optional Redemption. The Notes will be redeemable at any time, at the option of the Company, in whole
or from time to time in part, upon not less than 30 nor more than 60 days’ prior notice, on any date prior to their Maturity at a redemption price, calculated pursuant to the Indenture, which includes accrued interest thereon, if any, to, but
not including, the Redemption Date. In the case of any partial redemption, selection of the Notes for redemption will be made by the Trustee by such methods, as the Trustee in its sole discretion shall deem fair and appropriate. If any Note is to be
redeemed in part only, the notice of redemption relating to such Note shall state the portion of the principal amount thereof to be redeemed. A new Note in principal amount equal to the unredeemed portion thereof will be issued in the name of the
Holder thereof upon cancellation of this Note. 
 Repurchase upon a Change of Control Triggering Event. Upon the occurrence of a
Change of Control Triggering Event with respect to the Notes, the Company shall be required to make an offer to repurchase the Notes on the terms set forth in the Indenture. 

Defeasance and Covenant Defeasance. The Indenture contains provisions for defeasance at any time of (a) the entire indebtedness of
the Company on this Note and (b) certain restrictive covenants and the related Defaults and Events of Default, upon compliance by the Company with certain conditions set forth therein, which provisions apply to this Note. 

Modification and Waivers; Obligations of the Company Absolute. The Indenture permits, with certain exceptions as therein provided, the
amendment thereof and the modification of the rights and obligations of the Company and the rights of the Holders of the Securities of each Series. Such amendment may be effected under the Indenture at any time by the Company, and the Trustee with
the consent of the Holders of not less than a majority in aggregate principal amount of the outstanding Notes of each Series affected thereby. The Indenture also contains provisions permitting the Holders of not less than a majority in aggregate
principal amount of the Securities at the time outstanding, on behalf of the Holders of all outstanding Securities, to waive compliance by the Company with certain provisions of the Indenture. Furthermore, provisions in the Indenture permit the
Holders of not less than a majority in aggregate principal amount of the outstanding Securities of individual Series to waive on behalf of all of the Holders of Securities of such individual Series certain past defaults under the Indenture and their
consequences. Any such consent or waiver shall be conclusive and binding upon the Holder of this Note and upon all future Holders of this Note and of any Note issued upon the registration of transfer hereof or in exchange hereof or in lieu hereof,
whether or not notation of such consent or waiver is made upon this Note. 

  
 A-3 








 No reference herein to the Indenture and no provision of this Note or of the Indenture shall
alter or impair the obligation of the Company, which is absolute and unconditional, to pay the principal of and interest on this Note at the time, place, and rate, and in the coin or currency, herein prescribed. 

Limitation on Suits. As set forth in, and subject to, the provisions of the Indenture, no Holder of any Note will have any right to
institute any proceeding with respect to the Indenture or for any remedy thereunder, unless such Holder shall have previously given to the Trustee written notice of a continuing Event of Default with respect to this Series, the Holders of not less
than 25% in aggregate principal amount of the outstanding Notes shall have made written request, and offered indemnity or security, to the Trustee to institute such proceedings as trustee, and the Trustee shall not have received from the Holders of
a majority in principal amount of the outstanding Notes a direction inconsistent with such request and shall have failed to institute such proceeding within 60 days; provided, however, that such limitations do not apply to a suit
instituted by the Holder hereof for the enforcement of payment of the principal of or interest on this Note on or after the respective due dates expressed herein. 

Authorized Denominations. The Notes are issuable only in registered form without coupons in denominations of $2,000 or any integral
multiple of $1,000 in excess thereof. 
 Registration of Transfer or Exchange. As provided in the Indenture and subject to certain
limitations herein and therein set forth, the transfer of this Note is registrable in the register of the Notes maintained by the Registrar upon surrender of this Note for registration of transfer, at the office or agency of the Company in any place
where the principal of and interest on this Note are payable, duly endorsed by, or accompanied by a written instrument of transfer in form satisfactory to the Company and the Registrar, duly executed by the Holder hereof or his attorney duly
authorized in writing, and thereupon one or more new Notes, of authorized denominations and for the same aggregate principal amount, will be issued to the designated transferee or transferees. 

As provided in the Indenture and subject to certain limitations herein and therein set forth, the Notes are exchangeable for a like aggregate
principal amount of Notes of different authorized denominations, as requested by the Holders surrendering the same. 
 No service charge
shall be made for any such registration of transfer or exchange, but the Company may require payment of a sum sufficient to cover any tax or other governmental charge payable in connection therewith. 

Prior to due presentment of this Note for registration of transfer, the Company, the Trustee and any agent of the Company or the Trustee may
treat the Holder as the owner hereof for all purposes, whether or not this Note be overdue, and neither the Company, the Trustee nor any such agent shall be affected by notice to the contrary. 

Defined Terms. All terms used in this Note, which are defined in the Indenture and are not otherwise defined herein, shall have the
meanings assigned to them in the Indenture. 

  
 A-4 








 Governing Law. This Note shall be governed by and construed in accordance with the laws
of the State of New York. 
 Unless the certificate of authentication hereon has been executed by the Trustee by manual signature, this
Note shall not be entitled to any benefit under the Indenture or be valid or obligatory for any purpose. 
 [Remainder of page intentionally
left blank.] 

  
 A-5 








 IN WITNESS WHEREOF, the Company has caused this instrument to be duly executed and its seal to be
hereunto affixed and attested. 
 Dated: September     , 2015 

 

			
	BIOGEN INC.
		
	By:	 	  

	Name:	 	
	Title:	 	


  

			
	Attest:	 	
		
	By:	 	  

	Name:	 	
	Title:	 	


  
 A-6 








 TRUSTEE’S CERTIFICATE OF AUTHENTICATION 

This is one of the Notes of the Series designated and referred to in the within-mentioned Indenture, as such is supplemented by the
within-mentioned First Supplemental Indenture. 
  

			
	U.S. BANK NATIONAL ASSOCIATION, as Trustee
		
	By:	 	  

	Name:	 	
	Title:	 	


 Dated: September     , 2015 

  
 A-7 








 ASSIGNMENT 

FOR VALUE RECEIVED, the undersigned hereby sell(s), assign(s) and transfer(s) unto 
  

 
  

 
 PLEASE INSERT SOCIAL SECURITY NUMBER OR OTHER
IDENTIFYING NUMBER OF ASSIGNEE 
  

					
		  	    	  	

  
  

 
  

(Please print or typewrite name and address, 

including postal zip code, of assignee) 
 the
within Note and all rights thereunder, and hereby irrevocably constitutes and appoints 
  

 
  

 
  

 
 to transfer said Note on the books of the Trustee,
with full power of substitution in the premises. 
  

							
	 Dated:
	 	  
	 		 	  

		 		 		 	NOTICE: The signature to this assignment must correspond with the name as written upon the face of the within Note in every particular, without alteration or enlargement or any change whatsoever.
	  
	 		 	
	Signature Guarantee	 		 	


  
 A-8 








 EXHIBIT B 

FORM OF 3.625% SENIOR NOTE DUE 2022 

THIS NOTE IS A GLOBAL SECURITY WITHIN THE MEANING OF THE INDENTURE HEREINAFTER REFERRED TO AND IS REGISTERED IN THE NAME OF THE DEPOSITARY OR
A NOMINEE OF THE DEPOSITARY. THIS NOTE IS EXCHANGEABLE FOR NOTES REGISTERED IN THE NAME OF A PERSON OTHER THAN THE DEPOSITARY OR ITS NOMINEE ONLY IN THE LIMITED CIRCUMSTANCES DESCRIBED IN THE INDENTURE, AND MAY NOT BE TRANSFERRED EXCEPT AS A WHOLE
BY THE DEPOSITARY TO A NOMINEE OF THE DEPOSITARY, BY A NOMINEE OF THE DEPOSITARY TO THE DEPOSITARY OR ANOTHER NOMINEE OF THE DEPOSITARY OR BY THE DEPOSITARY OR ANY SUCH NOMINEE TO A SUCCESSOR DEPOSITARY OR A NOMINEE OF SUCH A SUCCESSOR DEPOSITARY.

 UNLESS THIS GLOBAL SECURITY IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION
(“DTC”), TO THE ISSUER OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY GLOBAL SECURITY ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR IN SUCH OTHER NAME AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF
DTC (AND ANY PAYMENT IS MADE TO CEDE & CO. OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE
REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN. 
 BIOGEN INC. 

3.625% Senior Note due 2022 
  

			
	REGISTERED	 	PRINCIPAL AMOUNT
	No.	 	$        

 CUSIP: 
 ISIN: 

Biogen Inc., a Delaware corporation (herein called the “Company,” which term includes any successor Person under the Indenture
hereinafter referred to), for value received, hereby promises to pay to Cede & Co., or registered assigns, the principal sum of $ on September 15, 2022 (the “Maturity Date”) (except to the extent redeemed or repaid prior to
the Maturity Date) and to pay interest thereon from September 15, 2015 (the “Original Issue Date”) or from the most recent Interest Payment Date to which interest has been paid or duly provided for semi-annually at the rate of
3.625% per annum, on March 15 and September 15 (each such date, an “Interest Payment Date”), commencing March 15, 2016, until the principal hereof is paid or made available for payment. 

  
 B-1 








 Payment of Interest. The interest so payable, and punctually paid or made available for
payment, on any Interest Payment Date, will, as provided in the Indenture, be paid, in immediately available funds, to the Person in whose name this Note (or one or more Predecessor Securities) is registered at the close of business on March 1
or September 1 (whether or not a Business Day, as defined in the Indenture), as the case may be, next preceding such Interest Payment Date (the “Regular Record Date”). Any such interest not punctually paid or duly provided for
(“Defaulted Interest”) will forthwith cease to be payable to the Holder on such Regular Record Date, and such Defaulted Interest, may be paid to the Person in whose name this Note (or one or more Predecessor Securities) is registered at
the close of business on a special record date (the “Special Record Date”) for the payment of such Defaulted Interest to be fixed by the Trustee, notice whereof shall be given to Holders of Notes not less than fifteen days prior to such
Special Record Date, or may be paid at any time in any other lawful manner not inconsistent with requirements of any securities exchange on which the Notes may be listed, and upon such notice as may be required by such exchange, all as more fully
provided in said Indenture. 
 Place of Payment. Payment of principal, premium, if any, and interest on this Note will be made at the
Corporate Trust Office of the Trustee or such other office or agency of the Company as may be designated for such purpose, in such coin or currency of the United States of America as at the time of payment is legal tender for payment of public and
private debts; provided, however, that each installment of interest, premium, if any, and principal on this Note may at the Company’s option be paid in immediately available funds by transfer to an account maintained by the payee
located in the United States. 
 Time of Payment. In any case where any Interest Payment Date, the Maturity Date or any date fixed
for redemption or repayment of the Notes shall not be a Business Day, then (notwithstanding any other provision of the Indenture or this Note), payment of principal or interest, if any, need not be made on such date, but may be made on the next
succeeding Business Day with the same force and effect as if made on such Interest Payment Date, the Maturity Date or the date so fixed for redemption or repayment, and no interest shall accrue in respect of the delay. 

General. This Note is one of a duly authorized issue of Securities of the Company, issued and to be issued in one or more Series under
an indenture (the “Base Indenture”), dated as of September 15, 2015, between the Company and U.S. Bank National Association (herein called the “Trustee,” which term includes any successor trustee under the Indenture with
respect to a Series of which this Note is a part), as supplemented by a First Supplemental Indenture thereto, dated as of September 15, 2015 (the “First Supplemental Indenture” and, together with the Base Indenture, the
“Indenture”). Reference is hereby made to the Indenture for a statement of the respective rights, limitations of rights, duties and immunities thereunder of the Company, the Trustee and the Holders of the Securities, and of the terms upon
which the Securities are, and are to be, authenticated and delivered. This Note is one of a duly authorized Series of Securities designated as “3.625% Senior Notes due 2022” (collectively, the “Notes”), initially limited in
aggregate principal amount to $        . 

  
 B-2 








 Further Issuance. The Company may from time to time, without the consent of the Holders of
the Notes, issue additional Securities (the “Additional Securities”) of this Series having the same ranking and the same interest rate, maturity and other terms as the Notes. Any Additional Securities of this Series and the Notes will
constitute a single Series under the Indenture and all references to the Notes shall include the Additional Securities unless the context otherwise requires. 

Events of Default. If an Event of Default with respect to the Notes shall have occurred and be continuing, the principal of the Notes
may be declared due and payable in the manner and with the effect provided in the Indenture. 
 Sinking Fund. The Notes are not
subject to any sinking fund. 
 Optional Redemption. The Notes will be redeemable at any time, at the option of the Company, in whole
or from time to time in part, upon not less than 30 nor more than 60 days’ prior notice, on any date prior to their Maturity at a redemption price, calculated pursuant to the Indenture, which includes accrued interest thereon, if any, to, but
not including, the Redemption Date. In the case of any partial redemption, selection of the Notes for redemption will be made by the Trustee by such methods, as the Trustee in its sole discretion shall deem fair and appropriate. If any Note is to be
redeemed in part only, the notice of redemption relating to such Note shall state the portion of the principal amount thereof to be redeemed. A new Note in principal amount equal to the unredeemed portion thereof will be issued in the name of the
Holder thereof upon cancellation of this Note. 
 Repurchase upon a Change of Control Triggering Event. Upon the occurrence of a
Change of Control Triggering Event with respect to the Notes, the Company shall be required to make an offer to repurchase the Notes on the terms set forth in the Indenture. 

Defeasance and Covenant Defeasance. The Indenture contains provisions for defeasance at any time of (a) the entire indebtedness of
the Company on this Note and (b) certain restrictive covenants and the related Defaults and Events of Default, upon compliance by the Company with certain conditions set forth therein, which provisions apply to this Note. 

Modification and Waivers; Obligations of the Company Absolute. The Indenture permits, with certain exceptions as therein provided, the
amendment thereof and the modification of the rights and obligations of the Company and the rights of the Holders of the Securities of each Series. Such amendment may be effected under the Indenture at any time by the Company, and the Trustee with
the consent of the Holders of not less than a majority in aggregate principal amount of the outstanding Notes of each Series affected thereby. The Indenture also contains provisions permitting the Holders of not less than a majority in aggregate
principal amount of the Securities at the time outstanding, on behalf of the Holders of all outstanding Securities, to waive compliance by the Company with certain provisions of the Indenture. Furthermore, provisions in the Indenture permit the
Holders of not less than a majority in aggregate principal amount of the outstanding Securities of individual Series to waive on behalf of all of the Holders of Securities of such individual Series certain past defaults under the Indenture and their
consequences. Any such consent or waiver shall be conclusive and binding upon the Holder of this Note and upon all future Holders of this Note and of any Note issued upon the registration of transfer hereof or in exchange hereof or in lieu hereof,
whether or not notation of such consent or waiver is made upon this Note. 

  
 B-3 








 No reference herein to the Indenture and no provision of this Note or of the Indenture shall
alter or impair the obligation of the Company, which is absolute and unconditional, to pay the principal of and interest on this Note at the time, place, and rate, and in the coin or currency, herein prescribed. 

Limitation on Suits. As set forth in, and subject to, the provisions of the Indenture, no Holder of any Note will have any right to
institute any proceeding with respect to the Indenture or for any remedy thereunder, unless such Holder shall have previously given to the Trustee written notice of a continuing Event of Default with respect to this Series, the Holders of not less
than 25% in aggregate principal amount of the outstanding Notes shall have made written request, and offered indemnity or security, to the Trustee to institute such proceedings as trustee, and the Trustee shall not have received from the Holders of
a majority in principal amount of the outstanding Notes a direction inconsistent with such request and shall have failed to institute such proceeding within 60 days; provided, however, that such limitations do not apply to a suit
instituted by the Holder hereof for the enforcement of payment of the principal of or interest on this Note on or after the respective due dates expressed herein. 

Authorized Denominations. The Notes are issuable only in registered form without coupons in denominations of $2,000 or any integral
multiple of $1,000 in excess thereof. 
 Registration of Transfer or Exchange. As provided in the Indenture and subject to certain
limitations herein and therein set forth, the transfer of this Note is registrable in the register of the Notes maintained by the Registrar upon surrender of this Note for registration of transfer, at the office or agency of the Company in any place
where the principal of and interest on this Note are payable, duly endorsed by, or accompanied by a written instrument of transfer in form satisfactory to the Company and the Registrar, duly executed by the Holder hereof or his attorney duly
authorized in writing, and thereupon one or more new Notes, of authorized denominations and for the same aggregate principal amount, will be issued to the designated transferee or transferees. 

As provided in the Indenture and subject to certain limitations herein and therein set forth, the Notes are exchangeable for a like aggregate
principal amount of Notes of different authorized denominations, as requested by the Holders surrendering the same. 
 No service charge
shall be made for any such registration of transfer or exchange, but the Company may require payment of a sum sufficient to cover any tax or other governmental charge payable in connection therewith. 

Prior to due presentment of this Note for registration of transfer, the Company, the Trustee and any agent of the Company or the Trustee may
treat the Holder as the owner hereof for all purposes, whether or not this Note be overdue, and neither the Company, the Trustee nor any such agent shall be affected by notice to the contrary. 

Defined Terms. All terms used in this Note, which are defined in the Indenture and are not otherwise defined herein, shall have the
meanings assigned to them in the Indenture. 

  
 B-4 








 Governing Law. This Note shall be governed by and construed in accordance with the laws
of the State of New York. 
 Unless the certificate of authentication hereon has been executed by the Trustee by manual signature, this
Note shall not be entitled to any benefit under the Indenture or be valid or obligatory for any purpose. 
 [Remainder of page intentionally
left blank.] 

  
 B-5 








 IN WITNESS WHEREOF, the Company has caused this instrument to be duly executed and its seal to be
hereunto affixed and attested. 
 Dated: September , 2015 
  

			
	BIOGEN INC.
		
	By:	 	  

	Name:	 	
	Title:	 	


  

			
	Attest:
		
	By:	 	  

	Name:	 	
	Title:	 	


  
 B-6 








 TRUSTEE’S CERTIFICATE OF AUTHENTICATION 

This is one of the Notes of the Series designated and referred to in the within-mentioned Indenture, as such is supplemented by the
within-mentioned First Supplemental Indenture. 
  

			
	U.S. BANK NATIONAL ASSOCIATION, as Trustee
		
	By:	 	  

	Name:	 	
	Title:	 	


 Dated: September    , 2015 

  
 B-7 








 ASSIGNMENT 

FOR VALUE RECEIVED, the undersigned hereby sell(s), assign(s) and transfer(s) unto 
  

 
  

 
 PLEASE INSERT SOCIAL SECURITY NUMBER OR OTHER
IDENTIFYING NUMBER OF ASSIGNEE 
  

					
		  	    	  	

  
  

 
  

(Please print or typewrite name and address, 

including postal zip code, of assignee) 
 the
within Note and all rights thereunder, and hereby irrevocably constitutes and appoints 
  

 
  

 
  

 
 to transfer said Note on the books of the Trustee,
with full power of substitution in the premises. 
  

							
	 Dated:
	 	  
	 		 	  

		 		 		 	NOTICE: The signature to this assignment must correspond with the name as written upon the face of the within Note in every particular, without alteration or enlargement or any change whatsoever.
	  
	 		 	
	Signature Guarantee	 		 	


  
 B-8 








 EXHIBIT C 

FORM OF 4.050% SENIOR NOTE DUE 2025 

THIS NOTE IS A GLOBAL SECURITY WITHIN THE MEANING OF THE INDENTURE HEREINAFTER REFERRED TO AND IS REGISTERED IN THE NAME OF THE DEPOSITARY OR
A NOMINEE OF THE DEPOSITARY. THIS NOTE IS EXCHANGEABLE FOR NOTES REGISTERED IN THE NAME OF A PERSON OTHER THAN THE DEPOSITARY OR ITS NOMINEE ONLY IN THE LIMITED CIRCUMSTANCES DESCRIBED IN THE INDENTURE, AND MAY NOT BE TRANSFERRED EXCEPT AS A WHOLE
BY THE DEPOSITARY TO A NOMINEE OF THE DEPOSITARY, BY A NOMINEE OF THE DEPOSITARY TO THE DEPOSITARY OR ANOTHER NOMINEE OF THE DEPOSITARY OR BY THE DEPOSITARY OR ANY SUCH NOMINEE TO A SUCCESSOR DEPOSITARY OR A NOMINEE OF SUCH A SUCCESSOR DEPOSITARY.

 UNLESS THIS GLOBAL SECURITY IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION
(“DTC”), TO THE ISSUER OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY GLOBAL SECURITY ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR IN SUCH OTHER NAME AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF
DTC (AND ANY PAYMENT IS MADE TO CEDE & CO. OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE
REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN. 
 BIOGEN INC. 

4.050% Senior Note due 2025 
  

			
	 REGISTERED
 No.
	 	 PRINCIPAL AMOUNT

$        

		
	 CUSIP:
 ISIN:
	 	

 Biogen Inc., a Delaware corporation (herein called the “Company,” which term includes any successor
Person under the Indenture hereinafter referred to), for value received, hereby promises to pay to Cede & Co., or registered assigns, the principal sum of $ on September 15, 2025 (the “Maturity Date”) (except to the extent
redeemed or repaid prior to the Maturity Date) and to pay interest thereon from September 15, 2015 (the “Original Issue Date”) or from the most recent Interest Payment Date to which interest has been paid or duly provided for
semi-annually at the rate of 4.050% per annum, on March 15 and September 15 (each such date, an “Interest Payment Date”), commencing March 15, 2016, until the principal hereof is paid or made available for payment. 


  
 C-1 








 Payment of Interest. The interest so payable, and punctually paid or made available for
payment, on any Interest Payment Date, will, as provided in the Indenture, be paid, in immediately available funds, to the Person in whose name this Note (or one or more Predecessor Securities) is registered at the close of business on March 1
or September 1 (whether or not a Business Day, as defined in the Indenture), as the case may be, next preceding such Interest Payment Date (the “Regular Record Date”). Any such interest not punctually paid or duly provided for
(“Defaulted Interest”) will forthwith cease to be payable to the Holder on such Regular Record Date, and such Defaulted Interest, may be paid to the Person in whose name this Note (or one or more Predecessor Securities) is registered at
the close of business on a special record date (the “Special Record Date”) for the payment of such Defaulted Interest to be fixed by the Trustee, notice whereof shall be given to Holders of Notes not less than fifteen days prior to such
Special Record Date, or may be paid at any time in any other lawful manner not inconsistent with requirements of any securities exchange on which the Notes may be listed, and upon such notice as may be required by such exchange, all as more fully
provided in said Indenture. 
 Place of Payment. Payment of principal, premium, if any, and interest on this Note will be made at the
Corporate Trust Office of the Trustee or such other office or agency of the Company as may be designated for such purpose, in such coin or currency of the United States of America as at the time of payment is legal tender for payment of public and
private debts; provided, however, that each installment of interest, premium, if any, and principal on this Note may at the Company’s option be paid in immediately available funds by transfer to an account maintained by the payee
located in the United States. 
 Time of Payment. In any case where any Interest Payment Date, the Maturity Date or any date fixed
for redemption or repayment of the Notes shall not be a Business Day, then (notwithstanding any other provision of the Indenture or this Note), payment of principal or interest, if any, need not be made on such date, but may be made on the next
succeeding Business Day with the same force and effect as if made on such Interest Payment Date, the Maturity Date or the date so fixed for redemption or repayment, and no interest shall accrue in respect of the delay. 

General. This Note is one of a duly authorized issue of Securities of the Company, issued and to be issued in one or more Series under
an indenture (the “Base Indenture”), dated as of September 15, 2015, between the Company and U.S. Bank National Association (herein called the “Trustee,” which term includes any successor trustee under the Indenture with
respect to a Series of which this Note is a part), as supplemented by a First Supplemental Indenture thereto, dated as of September 15, 2015 (the “First Supplemental Indenture” and, together with the Base Indenture, the
“Indenture”). Reference is hereby made to the Indenture for a statement of the respective rights, limitations of rights, duties and immunities thereunder of the Company, the Trustee and the Holders of the Securities, and of the terms upon
which the Securities are, and are to be, authenticated and delivered. This Note is one of a duly authorized Series of Securities designated as “4.050% Senior Notes due 2025” (collectively, the “Notes”), initially limited in
aggregate principal amount to $        . 

  
 C-2 








 Further Issuance. The Company may from time to time, without the consent of the Holders of
the Notes, issue additional Securities (the “Additional Securities”) of this Series having the same ranking and the same interest rate, maturity and other terms as the Notes. Any Additional Securities of this Series and the Notes will
constitute a single Series under the Indenture and all references to the Notes shall include the Additional Securities unless the context otherwise requires. 

Events of Default. If an Event of Default with respect to the Notes shall have occurred and be continuing, the principal of the Notes
may be declared due and payable in the manner and with the effect provided in the Indenture. 
 Sinking Fund. The Notes are not
subject to any sinking fund. 
 Optional Redemption. The Notes will be redeemable at any time, at the option of the Company, in whole
or from time to time in part, upon not less than 30 nor more than 60 days’ prior notice, on any date prior to their Maturity at a redemption price, calculated pursuant to the Indenture, which includes accrued interest thereon, if any, to, but
not including, the Redemption Date. In the case of any partial redemption, selection of the Notes for redemption will be made by the Trustee by such methods, as the Trustee in its sole discretion shall deem fair and appropriate. If any Note is to be
redeemed in part only, the notice of redemption relating to such Note shall state the portion of the principal amount thereof to be redeemed. A new Note in principal amount equal to the unredeemed portion thereof will be issued in the name of the
Holder thereof upon cancellation of this Note. 
 Repurchase upon a Change of Control Triggering Event. Upon the occurrence of a
Change of Control Triggering Event with respect to the Notes, the Company shall be required to make an offer to repurchase the Notes on the terms set forth in the Indenture. 

Defeasance and Covenant Defeasance. The Indenture contains provisions for defeasance at any time of (a) the entire indebtedness of
the Company on this Note and (b) certain restrictive covenants and the related Defaults and Events of Default, upon compliance by the Company with certain conditions set forth therein, which provisions apply to this Note. 

Modification and Waivers; Obligations of the Company Absolute. The Indenture permits, with certain exceptions as therein provided, the
amendment thereof and the modification of the rights and obligations of the Company and the rights of the Holders of the Securities of each Series. Such amendment may be effected under the Indenture at any time by the Company, and the Trustee with
the consent of the Holders of not less than a majority in aggregate principal amount of the outstanding Notes of each Series affected thereby. The Indenture also contains provisions permitting the Holders of not less than a majority in aggregate
principal amount of the Securities at the time outstanding, on behalf of the Holders of all outstanding Securities, to waive compliance by the Company with certain provisions of the Indenture. Furthermore, provisions in the Indenture permit the
Holders of not less than a majority in aggregate principal amount of the outstanding Securities of individual Series to waive on behalf of all of the Holders of Securities of such individual Series certain past defaults under the Indenture and their
consequences. Any such consent or waiver shall be conclusive and binding upon the Holder of this Note and upon all future Holders of this Note and of any Note issued upon the registration of transfer hereof or in exchange hereof or in lieu hereof,
whether or not notation of such consent or waiver is made upon this Note. 

  
 C-3 








 No reference herein to the Indenture and no provision of this Note or of the Indenture shall
alter or impair the obligation of the Company, which is absolute and unconditional, to pay the principal of and interest on this Note at the time, place, and rate, and in the coin or currency, herein prescribed. 

Limitation on Suits. As set forth in, and subject to, the provisions of the Indenture, no Holder of any Note will have any right to
institute any proceeding with respect to the Indenture or for any remedy thereunder, unless such Holder shall have previously given to the Trustee written notice of a continuing Event of Default with respect to this Series, the Holders of not less
than 25% in aggregate principal amount of the outstanding Notes shall have made written request, and offered indemnity or security, to the Trustee to institute such proceedings as trustee, and the Trustee shall not have received from the Holders of
a majority in principal amount of the outstanding Notes a direction inconsistent with such request and shall have failed to institute such proceeding within 60 days; provided, however, that such limitations do not apply to a suit
instituted by the Holder hereof for the enforcement of payment of the principal of or interest on this Note on or after the respective due dates expressed herein. 

Authorized Denominations. The Notes are issuable only in registered form without coupons in denominations of $2,000 or any integral
multiple of $1,000 in excess thereof. 
 Registration of Transfer or Exchange. As provided in the Indenture and subject to certain
limitations herein and therein set forth, the transfer of this Note is registrable in the register of the Notes maintained by the Registrar upon surrender of this Note for registration of transfer, at the office or agency of the Company in any place
where the principal of and interest on this Note are payable, duly endorsed by, or accompanied by a written instrument of transfer in form satisfactory to the Company and the Registrar, duly executed by the Holder hereof or his attorney duly
authorized in writing, and thereupon one or more new Notes, of authorized denominations and for the same aggregate principal amount, will be issued to the designated transferee or transferees. 

As provided in the Indenture and subject to certain limitations herein and therein set forth, the Notes are exchangeable for a like aggregate
principal amount of Notes of different authorized denominations, as requested by the Holders surrendering the same. 
 No service charge
shall be made for any such registration of transfer or exchange, but the Company may require payment of a sum sufficient to cover any tax or other governmental charge payable in connection therewith. 

Prior to due presentment of this Note for registration of transfer, the Company, the Trustee and any agent of the Company or the Trustee may
treat the Holder as the owner hereof for all purposes, whether or not this Note be overdue, and neither the Company, the Trustee nor any such agent shall be affected by notice to the contrary. 

Defined Terms. All terms used in this Note, which are defined in the Indenture and are not otherwise defined herein, shall have the
meanings assigned to them in the Indenture. 

  
 C-4 








 Governing Law. This Note shall be governed by and construed in accordance with the laws
of the State of New York. 
 Unless the certificate of authentication hereon has been executed by the Trustee by manual signature, this
Note shall not be entitled to any benefit under the Indenture or be valid or obligatory for any purpose. 
 [Remainder of page intentionally
left blank.] 

  
 C-5 








 IN WITNESS WHEREOF, the Company has caused this instrument to be duly executed and its seal to be
hereunto affixed and attested. 
 Dated: September     , 2015 

 

			
	BIOGEN INC.
		
	By:	 	  

	Name:	 	
	Title:	 	


  

			
	Attest:
		
	By:	 	  

	Name:	 	
	Title:	 	


  
 C-6 








 TRUSTEE’S CERTIFICATE OF AUTHENTICATION 

This is one of the Notes of the Series designated and referred to in the within-mentioned Indenture, as such is supplemented by the
within-mentioned First Supplemental Indenture. 
  

			
	U.S. BANK NATIONAL ASSOCIATION, as Trustee
		
	By:	 	  

	Name:	 	
	Title:	 	


 Dated: September     , 2015 

  
 C-7 








 ASSIGNMENT 

FOR VALUE RECEIVED, the undersigned hereby sell(s), assign(s) and transfer(s) unto 
  

 
  

 
 PLEASE INSERT SOCIAL SECURITY NUMBER OR OTHER
IDENTIFYING NUMBER OF ASSIGNEE 
  

					
		  	    	  	

  
  

 
  

(Please print or typewrite name and address, 

including postal zip code, of assignee) 
 the
within Note and all rights thereunder, and hereby irrevocably constitutes and appoints 
  

 
  

 
  

 
 to transfer said Note on the books of the Trustee,
with full power of substitution in the premises. 
  

							
	 Dated:
	 	  
	 		 	  

		 		 		 	NOTICE: The signature to this assignment must correspond with the name as written upon the face of the within Note in every particular, without alteration or enlargement or any change whatsoever.
	  
	 		 	
	Signature Guarantee	 		 	


  
 C-8 








 EXHIBIT D 

FORM OF 5.200% SENIOR NOTE DUE 2045 

THIS NOTE IS A GLOBAL SECURITY WITHIN THE MEANING OF THE INDENTURE HEREINAFTER REFERRED TO AND IS REGISTERED IN THE NAME OF THE DEPOSITARY OR
A NOMINEE OF THE DEPOSITARY. THIS NOTE IS EXCHANGEABLE FOR NOTES REGISTERED IN THE NAME OF A PERSON OTHER THAN THE DEPOSITARY OR ITS NOMINEE ONLY IN THE LIMITED CIRCUMSTANCES DESCRIBED IN THE INDENTURE, AND MAY NOT BE TRANSFERRED EXCEPT AS A WHOLE
BY THE DEPOSITARY TO A NOMINEE OF THE DEPOSITARY, BY A NOMINEE OF THE DEPOSITARY TO THE DEPOSITARY OR ANOTHER NOMINEE OF THE DEPOSITARY OR BY THE DEPOSITARY OR ANY SUCH NOMINEE TO A SUCCESSOR DEPOSITARY OR A NOMINEE OF SUCH A SUCCESSOR DEPOSITARY.

 UNLESS THIS GLOBAL SECURITY IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION
(“DTC”), TO THE ISSUER OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY GLOBAL SECURITY ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR IN SUCH OTHER NAME AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF
DTC (AND ANY PAYMENT IS MADE TO CEDE & CO. OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE
REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN. 
 BIOGEN INC. 

5.200% Senior Note due 2045 
  

			
	REGISTERED	 	PRINCIPAL AMOUNT
	No.	 	$        

 CUSIP: 
 ISIN: 

Biogen Inc., a Delaware corporation (herein called the “Company,” which term includes any successor Person under the Indenture
hereinafter referred to), for value received, hereby promises to pay to Cede & Co., or registered assigns, the principal sum of $ on September 15, 2045 (the “Maturity Date”) (except to the extent redeemed or repaid prior to
the Maturity Date) and to pay interest thereon from September 15, 2015 (the “Original Issue Date”) or from the most recent Interest Payment Date to which interest has been paid or duly provided for semi-annually at the rate of
5.200% per annum, on March 15 and September 15 (each such date, an “Interest Payment Date”), commencing March 15, 2016, until the principal hereof is paid or made available for payment. 

  
 D-1 








 Payment of Interest. The interest so payable, and punctually paid or made available for
payment, on any Interest Payment Date, will, as provided in the Indenture, be paid, in immediately available funds, to the Person in whose name this Note (or one or more Predecessor Securities) is registered at the close of business on March 1
or September 1 (whether or not a Business Day, as defined in the Indenture), as the case may be, next preceding such Interest Payment Date (the “Regular Record Date”). Any such interest not punctually paid or duly provided for
(“Defaulted Interest”) will forthwith cease to be payable to the Holder on such Regular Record Date, and such Defaulted Interest, may be paid to the Person in whose name this Note (or one or more Predecessor Securities) is registered at
the close of business on a special record date (the “Special Record Date”) for the payment of such Defaulted Interest to be fixed by the Trustee, notice whereof shall be given to Holders of Notes not less than fifteen days prior to such
Special Record Date, or may be paid at any time in any other lawful manner not inconsistent with requirements of any securities exchange on which the Notes may be listed, and upon such notice as may be required by such exchange, all as more fully
provided in said Indenture. 
 Place of Payment. Payment of principal, premium, if any, and interest on this Note will be made at the
Corporate Trust Office of the Trustee or such other office or agency of the Company as may be designated for such purpose, in such coin or currency of the United States of America as at the time of payment is legal tender for payment of public and
private debts; provided, however, that each installment of interest, premium, if any, and principal on this Note may at the Company’s option be paid in immediately available funds by transfer to an account maintained by the payee
located in the United States. 
 Time of Payment. In any case where any Interest Payment Date, the Maturity Date or any date fixed
for redemption or repayment of the Notes shall not be a Business Day, then (notwithstanding any other provision of the Indenture or this Note), payment of principal or interest, if any, need not be made on such date, but may be made on the next
succeeding Business Day with the same force and effect as if made on such Interest Payment Date, the Maturity Date or the date so fixed for redemption or repayment, and no interest shall accrue in respect of the delay. 

General. This Note is one of a duly authorized issue of Securities of the Company, issued and to be issued in one or more Series under
an indenture (the “Base Indenture”), dated as of September 15, 2015, between the Company and U.S. Bank National Association (herein called the “Trustee,” which term includes any successor trustee under the Indenture with
respect to a Series of which this Note is a part), as supplemented by a First Supplemental Indenture thereto, dated as of September 15, 2015 (the “First Supplemental Indenture” and, together with the Base Indenture, the
“Indenture”). Reference is hereby made to the Indenture for a statement of the respective rights, limitations of rights, duties and immunities thereunder of the Company, the Trustee and the Holders of the Securities, and of the terms upon
which the Securities are, and are to be, authenticated and delivered. This Note is one of a duly authorized Series of Securities designated as “5.200% Senior Notes due 2045” (collectively, the “Notes”), initially limited in
aggregate principal amount to $        . 

  
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 Further Issuance. The Company may from time to time, without the consent of the Holders of
the Notes, issue additional Securities (the “Additional Securities”) of this Series having the same ranking and the same interest rate, maturity and other terms as the Notes. Any Additional Securities of this Series and the Notes will
constitute a single Series under the Indenture and all references to the Notes shall include the Additional Securities unless the context otherwise requires. 

Events of Default. If an Event of Default with respect to the Notes shall have occurred and be continuing, the principal of the Notes
may be declared due and payable in the manner and with the effect provided in the Indenture. 
 Sinking Fund. The Notes are not
subject to any sinking fund. 
 Optional Redemption. The Notes will be redeemable at any time, at the option of the Company, in whole
or from time to time in part, upon not less than 30 nor more than 60 days’ prior notice, on any date prior to their Maturity at a redemption price, calculated pursuant to the Indenture, which includes accrued interest thereon, if any, to, but
not including, the Redemption Date. In the case of any partial redemption, selection of the Notes for redemption will be made by the Trustee by such methods, as the Trustee in its sole discretion shall deem fair and appropriate. If any Note is to be
redeemed in part only, the notice of redemption relating to such Note shall state the portion of the principal amount thereof to be redeemed. A new Note in principal amount equal to the unredeemed portion thereof will be issued in the name of the
Holder thereof upon cancellation of this Note. 
 Repurchase upon a Change of Control Triggering Event. Upon the occurrence of a
Change of Control Triggering Event with respect to the Notes, the Company shall be required to make an offer to repurchase the Notes on the terms set forth in the Indenture. 

Defeasance and Covenant Defeasance. The Indenture contains provisions for defeasance at any time of (a) the entire indebtedness of
the Company on this Note and (b) certain restrictive covenants and the related Defaults and Events of Default, upon compliance by the Company with certain conditions set forth therein, which provisions apply to this Note. 

Modification and Waivers; Obligations of the Company Absolute. The Indenture permits, with certain exceptions as therein provided, the
amendment thereof and the modification of the rights and obligations of the Company and the rights of the Holders of the Securities of each Series. Such amendment may be effected under the Indenture at any time by the Company, and the Trustee with
the consent of the Holders of not less than a majority in aggregate principal amount of the outstanding Notes of each Series affected thereby. The Indenture also contains provisions permitting the Holders of not less than a majority in aggregate
principal amount of the Securities at the time outstanding, on behalf of the Holders of all outstanding Securities, to waive compliance by the Company with certain provisions of the Indenture. Furthermore, provisions in the Indenture permit the
Holders of not less than a majority in aggregate principal amount of the outstanding Securities of individual Series to waive on behalf of all of the Holders of Securities of such individual Series certain past defaults under the Indenture and their
consequences. Any such consent or waiver shall be conclusive and binding upon the Holder of this Note and upon all future Holders of this Note and of any Note issued upon the registration of transfer hereof or in exchange hereof or in lieu hereof,
whether or not notation of such consent or waiver is made upon this Note. 

  
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 No reference herein to the Indenture and no provision of this Note or of the Indenture shall
alter or impair the obligation of the Company, which is absolute and unconditional, to pay the principal of and interest on this Note at the time, place, and rate, and in the coin or currency, herein prescribed. 

Limitation on Suits. As set forth in, and subject to, the provisions of the Indenture, no Holder of any Note will have any right to
institute any proceeding with respect to the Indenture or for any remedy thereunder, unless such Holder shall have previously given to the Trustee written notice of a continuing Event of Default with respect to this Series, the Holders of not less
than 25% in aggregate principal amount of the outstanding Notes shall have made written request, and offered indemnity or security, to the Trustee to institute such proceedings as trustee, and the Trustee shall not have received from the Holders of
a majority in principal amount of the outstanding Notes a direction inconsistent with such request and shall have failed to institute such proceeding within 60 days; provided, however, that such limitations do not apply to a suit
instituted by the Holder hereof for the enforcement of payment of the principal of or interest on this Note on or after the respective due dates expressed herein. 

Authorized Denominations. The Notes are issuable only in registered form without coupons in denominations of $2,000 or any integral
multiple of $1,000 in excess thereof. 
 Registration of Transfer or Exchange. As provided in the Indenture and subject to certain
limitations herein and therein set forth, the transfer of this Note is registrable in the register of the Notes maintained by the Registrar upon surrender of this Note for registration of transfer, at the office or agency of the Company in any place
where the principal of and interest on this Note are payable, duly endorsed by, or accompanied by a written instrument of transfer in form satisfactory to the Company and the Registrar, duly executed by the Holder hereof or his attorney duly
authorized in writing, and thereupon one or more new Notes, of authorized denominations and for the same aggregate principal amount, will be issued to the designated transferee or transferees. 

As provided in the Indenture and subject to certain limitations herein and therein set forth, the Notes are exchangeable for a like aggregate
principal amount of Notes of different authorized denominations, as requested by the Holders surrendering the same. 
 No service charge
shall be made for any such registration of transfer or exchange, but the Company may require payment of a sum sufficient to cover any tax or other governmental charge payable in connection therewith. 

Prior to due presentment of this Note for registration of transfer, the Company, the Trustee and any agent of the Company or the Trustee may
treat the Holder as the owner hereof for all purposes, whether or not this Note be overdue, and neither the Company, the Trustee nor any such agent shall be affected by notice to the contrary. 

Defined Terms. All terms used in this Note, which are defined in the Indenture and are not otherwise defined herein, shall have the
meanings assigned to them in the Indenture. 

  
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 Governing Law. This Note shall be governed by and construed in accordance with the laws
of the State of New York. 
 Unless the certificate of authentication hereon has been executed by the Trustee by manual signature, this
Note shall not be entitled to any benefit under the Indenture or be valid or obligatory for any purpose. 
 [Remainder of page intentionally
left blank.] 

  
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 IN WITNESS WHEREOF, the Company has caused this instrument to be duly executed and its seal to be
hereunto affixed and attested. 
 Dated: September     , 2015 

 

			
	BIOGEN INC.
		
	By:	 	  

	Name:	 	
	Title:	 	


  

			
	Attest:	 	
		
	By:	 	  

	Name:	 	
	Title:	 	


  
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 TRUSTEE’S CERTIFICATE OF AUTHENTICATION 

This is one of the Notes of the Series designated and referred to in the within-mentioned Indenture, as such is supplemented by the
within-mentioned First Supplemental Indenture. 
  

			
	U.S. BANK NATIONAL ASSOCIATION, as Trustee
		
	By:	 	  

	Name:	 	
	Title:	 	


 Dated: September     , 2015 

  
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 ASSIGNMENT 

FOR VALUE RECEIVED, the undersigned hereby sell(s), assign(s) and transfer(s) unto 
  

 
  

 
 PLEASE INSERT SOCIAL SECURITY NUMBER OR OTHER
IDENTIFYING NUMBER OF ASSIGNEE 
  

					
		  	    	  	

  
  

 
  

(Please print or typewrite name and address, 

including postal zip code, of assignee) 
 the
within Note and all rights thereunder, and hereby irrevocably constitutes and appoints 
  

 
  

 
  

 
 to transfer said Note on the books of the Trustee,
with full power of substitution in the premises. 
  

							
	 Dated:
	 	  
	 		 	  

		 		 		 	NOTICE: The signature to this assignment must correspond with the name as written upon the face of the within Note in every particular, without alteration or enlargement or any change whatsoever.
	  
	 		 	
	Signature Guarantee	 		 	


  
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