Execution Copy

Mark Timney
BY HAND/EMAIL
December 10, 2018
Dear Mark,
As an incentive to induce you to join The Medicines Company (the “Company”) as
its Chief Executive Officer, the Company agrees, on the terms and subject to the
conditions set forth in this letter (this “Agreement”), as follows:
1.
As used herein, the following terms shall have the following meanings:

1.1
“Cause” shall mean (i) conviction of (or the entry of a guilty plea or plea of
nolo contendere to) any felony or any crime involving moral turpitude or
dishonesty; (ii) commission of a willful act of fraud or dishonesty against the
Company or any of its affiliates; (iii) willful and material breach of the
Company’s or any of its affiliates’ written policies; (iv) intentional and
material damage to the Company’s or any of its affiliates’ property; (v)
materially unsatisfactory performance of your key duties, responsibilities or
objectives (other than by reason of your physical or mental illness, incapacity,
or disability), unless such unsatisfactory performance is cured within ninety
(90) days after written notice; provided, however, that such opportunity to cure
shall not be required where, in the Company’s determination, such unsatisfactory
performance is not capable of cure; or (vi) material breach of your
confidentiality obligations or duties under your non-disclosure, non-competition
or other similar agreement with the Company or any of its affiliates.

1.2
“Change in Control Event” means:

(i)
any sale or transfer of all or substantially all of the assets of the Company to
another corporation or entity, or any merger, consolidation or reorganization of
the Company into or with another corporation or entity, with the result that,
upon conclusion of the transaction, the voting securities of the Company
immediately prior thereto do not represent (either by remaining outstanding or
by being converted into voting securities of the surviving entity) more than 50%
of the combined voting power of the voting securities of the continuing or
surviving entity of such merger, consolidation or reorganization; or

(ii)
a disclosure that any person (as the term “person” is used in Section 13(d)(3)
or Section 14(d)(2) of the Exchange Act), other than (A) any shareholder who,
prior to the Company becoming subject to the reporting requirements of Section
13 of the Exchange Act, previously held at least 30% of the combined voting
power of outstanding voting securities of the Company, (B) the Company, or (C)
any corporation owned directly or indirectly by the stockholders of the Company
in substantially the same proportion as their ownership of stock of the Company,
has become the beneficial owner (as the term “beneficial owner” is defined under

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Rule 13d-3 or any successor rule or regulation thereto under the Exchange Act)
of securities representing 30% or more of the combined voting power of the then
outstanding voting securities of the Company; or
(iii)
such time as individuals who as of the date hereof constitute the Board of
Directors of the Company, and any new director (other than a director designated
by a person who has entered into an agreement with the Company to effect any
transaction described in clause (i) or (ii) of this section) whose election by
the Board or nomination for election by the Company’s stockholders was approved
by a vote of at least two thirds of the directors then still in office who were
either directors at the beginning of the period or whose election or whose
nomination for election was previously so approved, cease for any reason to
constitute a majority of the Board of Directors; or

(iv)
the liquidation or dissolution of the Company.

1.3
“Exchange Act” means the Securities Exchange Act of 1934, as amended.

1.4
“Good Reason” shall mean the Company’s taking any of the following actions,
which actions shall not have been cured within a 30-day period following written
notice by you: (A) the principal place of the performance of your
responsibilities is changed to a location outside of a 30 mile radius from the
Principal Location; (B) there is a material reduction in your title, authority,
duties, or responsibilities, without Cause; (C) there is a material reduction in
your annual base salary, unless such reduction is applicable generally to other
employees in your grade level; (D) there is a material reduction in your
benefits, bonus eligibility or equity eligibility, unless such material
reduction is also applicable to other employees in your grade level; or (E)
there is a material breach of the Company’s obligations to you.

1.5
“Payment Date” shall mean the 60th day following the Termination Date, provided
that you have executed the release provided in Section 5 hereof and have not
revoked the release within the applicable revocation period.

1.6
“Principal Location” shall mean the principal place of the performance of your
responsibilities.

1.7
“Termination Date” shall mean the date on which the termination of your
employment shall become effective.

1.8
“Termination Event” shall mean the termination of your employment during the one
(1) year period following the date of the consummation of a Change in Control
Event (i) by the Company without Cause or (ii) by you upon written notice given
within sixty (60) days following the date on which you know, or should
reasonably be expected to know, of the Company’s taking any action that
constitutes Good Reason.

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2.
If the Company terminates your employment other than for Cause, or if you
terminate your employment for Good Reason, and a Change in Control Event has not
been consummated prior to such termination, subject to Sections 4, 5, and 6
hereof, the Company will pay to you, and you will be entitled to receive:

(i)
for a period of eighteen (18) months after the Termination Date, continued
payment of your then-current annual base salary; provided that, in the event
that the termination arises as a result of a material reduction in your annual
base salary under item (C) of the definition of Good Reason, then the amount
payable under this Section 2(i) shall be determined using your annual base
salary prior to such salary reduction, and

(ii)
for a period of eighteen (18) months after the Termination Date, reimbursement
of COBRA health care premiums actually paid by you and payment by the Company
for reasonable outplacement assistance of your choosing; provided that the
payments provided in this Section 2(ii) shall terminate upon your commencing
employment with a new employer and, in any event, all payments must be made not
later than the end of the year following the year in which the expense was
incurred, and provided further, the health care reimbursement shall terminate in
the event that the payment is found to be discriminatory under the applicable
health care plan and instead the Employee shall receive a cash payment equal to
the expected reimbursement amount, paid in the same calendar year that the
applicable reimbursement amount would have been paid, and

(iii)
accelerated vesting, effective on the Payment Date, of all time-vested equity
awards previously granted to you and outstanding immediately prior to the
Termination Date that would have vested within eighteen (18) months after the
Termination Date (assuming that you had continued to be employed by the Company
during such eighteen (18) month period).

3.
If a Termination Event occurs, subject to Sections 4, 5, and 6 hereof, the
Company will pay to you, and you will be entitled to receive:

(i)
on the Payment Date, in a lump sum, an amount equal to the sum of (A) two (2)
years of your then current annual base salary, plus (B) two (2) times your
then-current annual bonus target; provided that, in the event that the
Termination Event arises as a result of a material reduction in your annual base
salary under item (C) of the definition of Good Reason, then the amount payable
under this Section 3(i) shall be determined using your annual base salary prior
to such salary reduction, and

(ii)
for a period of twenty-four (24) months after the Termination Date,
reimbursement of COBRA health care premiums actually paid by you and payment by
the Company for reasonable outplacement assistance of your choosing; provided
that the payments provided in this Section 3(ii) shall terminate upon your
commencing employment with a new employer and, in any event, all

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payments must be made not later than the end of the year following the year in
which the expense was incurred, and provided further, the health care
reimbursement shall terminate in the event that the payment is found to be
discriminatory under the applicable health care plan and instead the Employee
shall receive a cash payment equal to the expected reimbursement amount, paid in
the same calendar year that the applicable reimbursement amount would have been
paid, and
(iii)
accelerated vesting, effective on the Payment Date, of all equity awards
previously granted to you and outstanding immediately prior to the Termination
Date.

4.
Other Provisions Affecting Termination Benefits

4.1
In addition to any other amounts that may be payable to you hereunder, but
without duplication of the amounts payable to you pursuant to your employment
agreement with the Company, in the event of the termination of your employment
with the Company for any reason, the Company will pay you (or in the case of
death, your spouse and, in the event you have no spouse, your estate), your base
salary earned but not yet paid through the Termination Date, any vacation pay
accrued through the Termination Date payable pursuant to the Company’s policies
in effect from time to time, any unreimbursed business expenses incurred through
the Termination Date pursuant to the Company’s policies in effect from time to
time, and (except if the Company terminates your employment for Cause), any
bonus earned but not yet paid prior to your Termination Date. The Company will
pay the earned but unpaid bonus in accordance with the terms of the Company’s
Annual Incentive Plan.

4.2
The Company may withhold from any and all amounts payable under this Agreement
such federal, state, and local taxes as may be required to be withheld pursuant
to applicable law or regulation. Upon your termination of employment from the
Company, the Company may also offset amounts that you owe to the Company against
any amounts payable to you hereunder as permitted by law.

4.3
If your employment is terminated for any reason, you are not required to seek
other employment or attempt in any way to reduce any amounts payable to you
under this Agreement. The foregoing provision notwithstanding, if you obtain new
employment, the Company does not have any obligation to provide the payment of
COBRA premiums and outplacement services under Sections 2(ii) and 3(ii) of this
Agreement.

5.
In order to receive the payments and benefits provided in this Agreement, you
will be required to execute, effective as of the Termination Date, a general
release in favor of the Company, in form and substance reasonably satisfactory
to the Company.

6.
Section 409A

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6.1
Any provision in this Agreement (or any agreement or arrangement referenced
herein) that is inconsistent with the requirements of Section 409A of the
Internal Revenue Code of 1986, as amended (the “Code”), and the regulations
issued or to be issued by the Department of the Treasury thereunder (“Section
409A”), including the timing of any payment, shall be promptly amended in a
manner mutually agreed to by the parties hereto in good faith in order to
attempt to avoid triggering adverse tax consequences to you under Section 409A.

6.2
In the event any payment that is either received by you or paid by the Company
on your behalf, or any cash, property or any other benefit provided to you under
this Agreement or under any other plan, arrangement or agreement with the
Company or any other person is treated as contingent on a change of ownership or
control of the Company (or in the ownership of a substantial portion of the
assets of the Company) (collectively, the “Company Payments”), and is subject to
the tax (the “Excise Tax”) imposed by Section 4999 of the Code (or any successor
provision and any similar tax that may hereafter be imposed by any taxing
authority), the amount of the Company Payments shall be automatically reduced to
the maximum amount that can be paid such that no portion of the Company Payments
is subject to the Excise Tax; provided, however, that the reduction shall occur
only if the reduced Company Payments (after taking into account further
reductions for applicable federal, state and local income, social security and
other taxes) would be greater than the unreduced Company Payments minus (i) the
Excise Tax payable with respect to such Company Payments, and (ii) all
applicable federal, state and local income, social security and other taxes on
such Company Payments.

7.
By signing this Agreement, you acknowledge and reaffirm your obligation to keep
confidential all non-public information concerning the Company that you acquired
during the course of your employment with the Company, as stated more fully in
the Invention and Non-Disclosure Agreement, and your obligations not to compete
with the Company or to solicit or hire employees of the Company, as stated more
fully in the Non-Competition and Non-Solicitation Agreement, both of which
agreements you executed at the inception of your employment and which remain in
full force and effect following the termination of your employment.

8.
No supplement, modification, or amendment of this Agreement shall be binding
unless executed in writing by the parties hereto.

9.
This Agreement shall be binding upon and inure to the benefit of the parties
hereto and their respective successors and assigns. This Agreement is assignable
by the Company only to an entity that is owned, directly or indirectly, in whole
or in part by the Company or by any successor to the Company or an acquirer of
all or substantially all of the assets of the Company.

10.
Any provision contained herein to the contrary notwithstanding, if you are a
specified employee (as defined under Treasury Regulation Section 1.409A-1(i)) as
of the Termination Date, the Company shall withhold and accumulate all payments
under Sections 2 and 3 to which you would otherwise be entitled during the first
six (6) months

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after the Termination Date to the extent required for compliance with Section
409A. In such event, the Company shall distribute these payments to you (or your
beneficiary) in a single lump sum on the first day of the seventh month after
the Termination Date, or within thirty (30) days after the date of your death
after the Termination Date.

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Execution Copy

Please indicate your acceptance of and agreement to the foregoing by executing
the enclosed copy of this letter where indicated and returning it to me.
Very truly yours,
THE MEDICINES COMPANY
By: /s/ Stephen M. Rodin    
Name: Stephen M. Rodin
Title: General Counsel
ACCEPTED AND AGREED:

/s/ Mark Timney            
Mark Timney        December 10, 2018
NAME            Date

[Signature Page to Timney Severance Agreement]