Exhibit 10.1
  Via Hand Delivery
      
    
    Your employment with the Company will end on the Termination Date and
you will receive payments of any salary owed through the Termination
Date and any unused vacation time accrued through the Termination
Date;
    
    You may elect to purchase group medical insurance pursuant to the
federal COBRA law, 29 U.S.C. § 1161 et seq., for as long as, and to
the extent that, you remain eligible for COBRA continuation. You




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should consult the COBRA materials to be provided by the Company for details
regarding these benefits;
    
    All other benefits or compensation provided to you as
an employee of the Company, including life insurance
and long-term disability, will cease upon the
Termination Date, except that you are entitled to
receive your vested accrued benefits, if any, under
the Companys 401(k) Plan; and
    
    Vesting under any stock option grants you have
received from the Company ends on the Termination
Date. Nothing in this letter shall constitute a
waiver or amendment of any rights you may have under
any stock option grants you have received from the
Company. You will have a period of three (3) months
after the Termination Date to exercise all of the
options that have vested.
   1.
    
    Termination of Employment  Your employment with the Company shall terminate on the
Termination Date, without further notice from, or action on the part of, the Company and all
benefits of employment shall cease on the Termination Date. In the period prior to the
Termination Date, you will remain an employee of the Company and will transition your
responsibilities to other employees of the Company. In addition, effective as of the
Termination Date, you will no longer serve in any other capacity with the Company and you
hereby resign from any and all offices, trusteeships, committee memberships and fiduciary
capacities held with, or on behalf of, the Company or any benefit plans of the Company.2.
    
    Severance Benefits  Subject to your compliance with the terms of this letter
agreement, the Company will pay to you, and you will be entitled to receive, the following
(collectively, the Severance Benefits):
 (i)
    
    an amount equal to one (2) years of your current annual base salary, less
all applicable federal, state and local taxes, payable in one (1) lump sum on the
60th day following the Termination date provided that you have not
revoked your acceptance to the letter agreement within the applicable revocation
period set forth in Paragraph 16;
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(ii)
    
    for a period of twelve (12) months after the Termination Date,
reimbursement of COBRA health care premiums actually paid by you and payment by the
Company for reasonable outplacement of your choosing; provided that the payments
provided in this Paragraph 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(iii)
    
    accelerated vesting, effective on the Payment Date, of stock options
previously granted to you and outstanding immediately prior to the Termination Date
which would have vested within one (2) years after the Termination Date (assuming
that you had continued to be employed by the Company during such one (2) year
period).
 3.
    
    Full Discharge  You agree and acknowledge that the payments and benefits provided in
Paragraph 2 above: (a) are in full discharge of any and all liabilities and obligations of
the Company to you, monetarily or with respect to employee benefits or otherwise, including,
without limitation, any and all obligations arising under any alleged written or oral
employment agreement, policy, plan or procedure of the Company and/or any alleged
understanding or arrangement between you and the Company or any of its officers or directors;
and (b) exceed any payment, benefit, or other thing of value to which you might otherwise be
entitled but for this letter under any policy, plan or procedure of the Company or any prior
agreement between you and the Company.4.
    
    Release  In consideration of the payment and provision of the Severance Benefits,
you, for yourself and for your heirs, dependents, executors, legal representatives and assigns
(the Releasors), hereby fully, forever, irrevocably and unconditionally release, remise and
discharge: (i) the Company; (ii) its affiliates, subsidiaries and parent companies; (iii) any
of its or their insurers, employee benefit plans or funds, fiduciaries, trustees, agents,
attorneys, officers, directors, stockholders, and employees (each in their individual and
corporate capacities); and (iv) any of their successors and assigns (hereinafter, the
Released Parties) from any and all claims, charges, complaints, demands, actions, causes of
action, suits, rights, debts, sums of money, costs, accounts, reckonings, covenants,
contracts, agreements, promises, doings, omissions, damages, executions, obligations,
liabilities, and expenses (including attorneys fees and costs), of every kind and nature
which you (or any of the other Releasors) ever had or now have or may have against the
Released Parties arising out of your employment with and/or
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separation from the Company, or out of any other agreement, understanding, relationship
or arrangement with the Company including, but not limited to:
 (i)
    
    any agreement you have with the Company;(ii)
    
    all employment discrimination claims under Title VII of the Civil Rights
Act of 1964, 42 U.S.C. §2000e et seq., theAge Discrimination in Employment Act, 29 U.S.C. § 621 et seq.,
the Americans With Disabilities Act of 1990, 42 U.S.C., §12101 et
seq., the Family and Medical Leave Act, 29 U.S.C. § 2601 et
seq., the Older Workers Benefits Protection Act, the Equal Pay Act, the
Worker Adjustment Retraining and Notification Act, the Federal Fair Labor
Standards Act, any applicable Executive Order Programs and their state and
local counterparts, the New Jersey Law Against Discrimination, N.J.S.A. 10:5-1
et seq., all claims arising out of the Fair Credit Reporting Act, 15 U.S.C.
§1681 et seq., the Employee Retirement Income Security Act of 1974 (ERISA),
29 U.S.C. §1001 et seq., the New Jersey Conscientious Employee Protection Act,
N.J.S.A. 34:19-1 et seq., the New Jersey Family Leave Act,
N.J.S.A. 34:11B-1 et seq., the New Jersey Workers Compensation
Act, the New Jersey State Wage and Hour Law, the New Jersey Wage Payment Law
and the New Jersey Political Activities of Employees law, all as amended;(iii)
    
    all common law claims including, but not limited to, actions in tort,
defamation, infliction of emotional distress, detrimental reliance, wrongful
discharge and breach of contract; all claims arising under any policies, practices
or procedures of the Company; all claims to any non-vested ownership interest in the
Company, contractual or otherwise, including but not limited to claims to stock or
stock options;(iv)
    
    any other claim for damage arising out of your employment with or
separation from the Company (including a claim for retaliation) under any common law
theory or any federal, state or local statute or ordinance not expressly referenced
above; and(v)
    
    any claim for attorneys fees, costs, disbursements and the like.
 This release shall not apply with respect to (i) any rights or benefits to which Employee
is entitled hereunder or to the enforcement thereof, (ii) all rights to seek or obtain
unemployment compensation, and Company agrees not to contest any claims which Employee
may make for
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unemployment compensation benefits; (iii) all rights to vested benefits under any
retirement plan, health benefits plan or other employee benefit plan or program of
Company; and (iv) all rights Employee may have to seek indemnification and be indemnified
to the fullest extent permitted for former officers or employees under applicable law
and/or Companys organization documents and by-laws (including coverage under any
insurance that Company had, has or may obtain for the benefit of its former officers or
employees).
 5.
    
    Continuing Obligations
 (i)
    
    You acknowledge and reaffirm your obligation to keep confidential all
non-public information concerning the Company which 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; and(ii)
    
    You also agree to make yourself reasonably available and at no charge to
assist the Company in the prosecution and/or defense of any legal proceedings in
which your participation, as a witness or otherwise, may be required.
 6.
    
    Return of Company Property  You understand that you must return all property of the
Company. By signing this letter agreement, you confirm and acknowledge that you have returned
to the Company all keys, files, records (and copies thereof), equipment (including, but not
limited to, computer hardware, software and printers, wireless handheld devices, cellular
phones, pagers, etc.), Company identification, Company vehicles and any other Company-owned
property in your possession or control and have left intact all electronic Company documents,
including but not limited to those which you developed or help develop during your employment.
You further confirm that you have cancelled all accounts for your benefit, if any, in the
Companys name, including but not limited to, credit cards, telephone charge cards, cellular
phone and/or pager accounts and computer accounts.7.
    
    Business Expenses and Compensation  You acknowledge that you have been reimbursed by
the Company for all business expenses incurred in conjunction with the performance of your
employment and that no other reimbursements are owed to you. You further acknowledge that
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you have received payment in full for all services rendered in conjunction with your
employment by the Company and that no other compensation is owed to you.8.
    
    Non-Disparagement- You understand and agree that as a condition for payment to you of the
consideration described herein, you shall not make any false, disparaging or derogatory
statements to any media outlet, industry group, financial institution or current or former
employee, consultant, client or customer of the Company regarding the Company or any of its
directors, officers, employees, agents or representatives or about the Companys business
affairs and financial condition. The Company agrees that it will use commercially reasonable
efforts to ensure that its current executive officers and directors shall not make any false,
disparaging or derogatory statements about you to any media outlet, industry group, financial
institution or current or former employee, consultant, client or customer of the Company. You
agree that you will not make any statements whatsoever to any investors or media about the
Company or your departure from the Company and, if asked for any such statements, you will
refer such inquiries to Glenn Sblendorio or Leslie Rohrbacker.9.
    
    Reference  You are directed to have all inquiries for references regarding your
employment with the Company directed to Leslie Rohrbacker, Vice President, Head of Human
Resources.10.
    
    Amendment- This letter agreement shall be binding upon the parties and may not be modified
in any manner except by an instrument in writing of concurrent or subsequent date signed by
duly authorized representatives of the parties hereto. This letter agreement is binding upon
and shall inure to the benefit of the parties and their respective agents, assigns, heirs,
executors, successors and administrators.11.
    
    Waiver of Rights  No delay or omission by either party in exercising any right under
this letter agreement shall operate as a waiver of that or any other right. A waiver or
consent given by a party on any one occasion shall be effective only in that instance and
shall not be construed as a bar or waiver of any right on any other occasion.12.
    
    Validity- Should any provision of this letter agreement be declared or be determined by any
court of competent jurisdiction to be illegal or invalid, the validity of the remaining parts,
terms or provisions shall not be affected thereby and said illegal or invalid part, term or
provision shall be deemed not to be a part of this letter agreement.
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13.
    
    Confidentiality- You understand and agree that as a condition for payment to you of the
Severance Benefits, the terms and contents of this letter agreement, and the negotiations and
discussions resulting in this letter agreement, shall be maintained as confidential by you and
your agents and representatives and shall not be disclosed by you and your agents and
representatives to any person except: (i) to the extent required by federal or state law;
(ii) to your spouse, accountant and attorney (provided that they are notified of and comply
with this confidentiality provision); or (iii) as otherwise agreed to in writing by the
Company.14.
    
    Nature of Agreement  You understand and agree that this letter agreement is a
severance agreement and does not constitute an admission of liability or wrongdoing on the
part of the Company.15.
    
    Voluntary Assent  You affirm that, other than as set forth herein, no promises or
agreements of any kind have been made to or with you by any person or entity whatsoever to
cause you to sign this letter agreement, and that you fully understand the meaning and intent
of this letter agreement. You state and represent that you have had an opportunity to fully
discuss and review the terms of this letter agreement with an attorney. You further state and
represent that you have carefully read this letter agreement, understand the contents hereof,
freely and voluntarily assent to all of the terms and conditions hereof, and sign your name of
your own free act.16.
    
    Acknowledgement and Revocation  You acknowledge that you have been given at least
twenty-one (21) days to consider this letter agreement, and that the Company hereby advises
you to consult with an attorney of your own choosing prior to signing this agreement. You may
revoke your agreement to this letter agreement for a period of seven (7) days following the
date you deliver the signed agreement to the Company. Any revocation within this period must
be submitted in writing to the Company and state I hereby revoke my agreement to the letter
agreement dated October 1, 2009. The revocation must be delivered to, and received by, the
Company within seven (7) days after the day you deliver the signed agreement to the Company.
This agreement shall not become effective or enforceable until the revocation period has
expired without your having revoked your agreement.17.
    
    Applicable Law  This letter agreement shall be interpreted and construed by the laws
of the State of New Jersey, without regard to conflict of laws, provisions.
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18.
    
    Withholding  The Company may withhold from any amounts payable under this letter
such federal, state and local taxes as are required to be withheld (with respect to amounts
payable hereunder or under any benefit plan or arrangement maintained by the Company) pursuant
to any applicable law or regulation.19.
    
    Entire Agreement  This letter agreement contains and constitutes the entire
understanding and agreement between the parties hereto with respect to the termination of your
employment with the Company, the Severance Benefits and the release of claims against the
Company and cancels all previous oral and written negotiations, agreements, commitments,
writings in connection therewith. Nothing in this Paragraph 19, however, shall modify, cancel
or supersede your obligations set forth in Paragraph 5 herein.
  Very truly yours,
THE MEDICINES COMPANYBy:
    Leslie C. RohrbackerLeslie C. Rohrbacker, Vice President, Head ofHuman Resources  /s/ John Kelley
    
    Date: October 22, 2009John P. Kelley  Page 8 of 8