Document:

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                                                                   EXHIBIT 10.19

             THIS WARRANT AND THE SHARES OF COMMON STOCK ISSUED UPON
                ITS EXERCISE ARE SUBJECT TO THE RESTRICTIONS ON
                TRANSFER SET FORTH IN SECTION 4 OF THIS WARRANT

Warrant No. ____                                     Number of Shares: ________
                                                         (subject to adjustment)

Date of Issuance: October 19, 1999

                              The Medicines Company

                          Common Stock Purchase Warrant

                          (Void after October 19, 2004)

The Medicines Company, a Delaware corporation (the "Company"), for value
received, hereby certifies that ___________________, or its registered assigns
(the "Registered Holder"), is entitled, subject to the terms and conditions set
forth below, to purchase from the Company, at any time or from time to time on
or after the date of issuance and on or before 5:00 p.m. (Boston time) on
October ___, 2004, ________ shares of common stock, $0.01 par value per share
(the "Common Stock"), of the Company, at a purchase price of $4.32 per share.
The shares purchasable upon exercise of this Warrant, and the purchase price per
share, each as adjusted from time to time pursuant to the provisions of this
Warrant, are hereinafter referred to as the "Warrant Shares" and the "Purchase
Price," respectively.

This Warrant is being issued by the Company to the Registered Holder in
connection with the closing of the sale of the Registered Holder of an 8%
Convertible Note in the original principal amount of $________ and is one of a
series of common stock purchase warrants (the "Warrants") issued in connection
with the sale by the Company of 8% Convertible Notes in the aggregate original
principal amount of up to $6,000,000 (the "Notes").

         1.       EXERCISE.

                  (a)      This Warrant may be exercised by the Registered
Holder, in whole or in part, by surrendering this Warrant, with the exercise
form appended hereto as EXHIBIT I duly executed by the Registered Holder or by
the Registered Holder's duly authorized attorney, at the principal office of the
Company, or at such other office or agency as the Company may designate,
accompanied by payment in full, in lawful money of the United States, of the
Purchase Price payable in respect of the number of Warrant Shares purchased upon
such exercise.

                 (b)      The Registered Holder may, at its option, elect to
pay some or all of the Purchase Price payable upon an exercise of this Warrant
by canceling a portion of this Warrant

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exercisable for such number of Warrant Shares as is determined by dividing (i)
the total Purchase Price payable in respect of the number of Warrant Shares
being purchased upon such exercise by (ii) the excess of the Fair Market Value
per share of Common Stock (as defined below) as of the Exercise Date (as defined
in subsection 1(c) below) over the Purchase Price per share. If the Registered
Holder wishes to exercise this Warrant pursuant to this method of payment with
respect to the maximum number of Warrant Shares purchasable pursuant to this
method, then the number of Warrant Shares so purchasable shall be equal to the
total number of Warrant Shares, minus the product obtained by multiplying (x)
the total number of Warrant Shares by (y) a fraction, the numerator of which
shall be the Purchase Price per share and the denominator of which shall be the
Fair Market Value per share of Common Stock as of the Exercise Date. The Fair
Market Value per share of Common Stock shall be determined as follows:

                           (i)      If the Common Stock is listed on a national
securities exchange, the Nasdaq National Market or another nationally recognized
trading system as of the Exercise Date, the Fair Market Value per share of
Common Stock shall be deemed to be the average of the high and low reported sale
prices per share of Common Stock thereon on the trading day immediately
preceding the Exercise Date (provided that if no such price is reported on such
day, the Fair Market Value per share of Common Stock shall be determined
pursuant to clause (ii)).

                           (ii)     If the Common Stock is not listed on a
national securities exchange, the Nasdaq National Market or another nationally
recognized trading system as of the Exercise Date, the Fair Market Value per
share of Common Stock shall be deemed to be the amount most recently determined
by the Board of Directors to represent the fair market value per share of the
Common Stock (including without limitation a determination for purposes of
granting Common Stock options or issuing Common Stock under an employee benefit
plan of the Company); and, upon request of the Registered Holder, the Board of
Directors (or a representative thereof) shall promptly notify the Registered
Holder of the Fair Market Value per share of Common Stock. Notwithstanding the
foregoing, if the Board of Directors has not made such a determination within
the three-month period prior to the Exercise Date, then (A) the Board of
Directors shall make a determination of the Fair Market Value per share of the
Common Stock within 15 days of a request by the Registered Holder that it do so,
and (B) the exercise of this Warrant pursuant to this subsection 1(b) shall be
delayed until such determination is made.

                  (c)      Each exercise of this Warrant shall be deemed to have
been effected immediately prior to the close of business on the day on which
this Warrant shall have been surrendered to the Company as provided in
subsection 1(a) above (the "Exercise Date"). At such time, the person or persons
in whose name or names any certificates for Warrant Shares shall be issuable
upon such exercise as provided in subsection 1(d) below shall be deemed to have
become the holder or holders of record of the Warrant Shares represented by such
certificates.

                  (d)      As soon as practicable after the exercise of this
Warrant in full or in part, and in any event within 10 days thereafter, the
Company, at its expense, will cause to be issued in the name of, and delivered
to, the Registered Holder, or as such Holder (upon payment by such Holder of any
applicable transfer taxes) may direct:

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                           (i)      a certificate or certificates for the number
of full Warrant Shares to which the Registered Holder shall be entitled upon
such exercise plus, in lieu of any fractional share to which the Registered
Holder would otherwise be entitled, cash in an amount determined pursuant to
Section 3 hereof; and

                           (ii)     in case such exercise is in part only, a new
warrant or warrants (dated the date hereof) of like tenor, calling in the
aggregate on the face or faces thereof for the number of Warrant Shares equal
(without giving effect to any adjustment therein) to the number of such shares
called for on the face of this Warrant minus the sum of (a) the number of such
shares purchased by the Registered Holder upon such exercise plus (b) the number
of Warrant Shares (if any) covered by the portion of this Warrant canceled in
payment of the Purchase Price payable upon such exercise pursuant to subsection
1(b) above.

         2.       ADJUSTMENTS.

                  (a)      If the Company consummates an Investor Sale (as
defined in the Notes) for consideration per share (the "Investor Price") which
is less than the Purchase Price in effect immediately prior to such Investor
Sale, then, immediately upon, and only upon, the consummation of the first such
Investor Sale, the Purchase Price shall be adjusted to equal the Investor Price.
For purposes of this section consideration received by the Company shall be
computed as follows:

                           (I)      insofar as it consists of cash, be computed
at the aggregate of cash received by the Company, excluding amounts paid or
payable for accrued interest; and

                           (II)     insofar as it consists of property other
than cash, be computed at the fair market value thereof at the time of such
issue, as determined in good faith by the Board of Directors; and

                           (III)    in the shares in the Investor Sale are
issued together with other shares or securities or other assets of the Company
for consideration which covers both, be the proportion of such consideration so
received, computed as provided in clauses (I) and (II) above, as determined in
good faith by the Board of Directors.

                  (b)      If outstanding shares of the Company's Common Stock
shall be subdivided into a greater number of shares or a dividend in Common
Stock shall be paid in respect of Common Stock, the Purchase Price in effect
immediately prior to such subdivision or at the record date of such dividend
shall simultaneously with the effectiveness of such subdivision or immediately
after the record date of such dividend be proportionately reduced. If
outstanding shares of Common Stock shall be combined into a smaller number of
shares, the Purchase Price in effect immediately prior to such combination
shall, simultaneously with the effectiveness of such combination, be
proportionately increased.

                  (c)      When any adjustment is required to be made in the
Purchase Price under this Section 2, the number of Warrant Shares purchasable
upon the exercise of this Warrant shall be changed to the number determined by
dividing (i) an amount equal to the number of Warrant Shares issuable upon the
exercise of this Warrant immediately prior to such adjustment,

                                      -3-
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multiplied by the Purchase Price in effect immediately prior to such adjustment,
by (ii) the Purchase Price in effect immediately after such adjustment.

                  (d)      If there shall occur any capital reorganization or
reclassification of the Company's Common Stock (other than a change in par value
or a subdivision or combination as provided for in subsection 2(b) above), or
any consolidation or merger of the Company with or into another corporation, or
a transfer of all or substantially all of the assets of the Company, then, as
part of any such reorganization, reclassification, consolidation, merger or
sale, as the case may be, lawful provision shall be made so that the Registered
Holder of this Warrant shall have the right thereafter to receive upon the
exercise hereof the kind and amount of shares of stock or other securities or
property which such Registered Holder would have been entitled to receive if,
immediately prior to any such reorganization, reclassification, consolidation,
merger or sale, as the case may be, such Registered Holder had held the number
of shares of Common Stock which were then purchasable upon the exercise of this
Warrant. In any such case, appropriate adjustment (as reasonably determined in
good faith by the Board of Directors of the Company) shall be made in the
application of the provisions set forth herein with respect to the rights and
interests thereafter of the Registered Holder of this Warrant, such that the
provisions set forth in this Section 2 (including provisions with respect to
adjustment of the Purchase Price) shall thereafter be applicable, as nearly as
is reasonably practicable, in relation to any shares of stock or other
securities or property thereafter deliverable upon the exercise of this Warrant.

                  (e)      When any adjustment is required to be made in the
Purchase Price, the Company shall promptly mail to the Registered Holder a
certificate setting forth the Purchase Price after such adjustment and setting
forth a brief statement of the facts requiring such adjustment. Such certificate
shall also set forth the kind and amount of stock or other securities or
property into which this Warrant shall be exercisable following the occurrence
of any of the events specified in this Section 2.

         3.       FRACTIONAL SHARES. The Company shall not be required upon the
exercise of this Warrant to issue any fractional shares, but shall make an
adjustment therefor in cash on the basis of the Fair Market Value per share of
Common Stock, as determined pursuant to subsection 1(b) above.

         4.       REQUIREMENTS FOR TRANSFER.

                  (a)      This Warrant and the Warrant Shares shall not be sold
or transferred unless either (i) they first shall have been registered under the
Securities Act of 1933, as amended (the "Act"), or (ii) the Company first shall
have been furnished with an opinion of legal counsel, reasonably satisfactory to
the Company, to the effect that such sale or transfer is exempt from the
registration requirements of the Act.

                  (b)      Notwithstanding the foregoing, no registration or
opinion of counsel shall be required for (i) a transfer by a Registered Holder
which is a corporation to a wholly owned subsidiary of such corporation, a
transfer by a Registered Holder which is a partnership to a partner of such
partnership or a retired partner of such partnership or to the estate of any
such partner or retired partner, a transfer by a Registered Holder who is an
individual to any members of such

                                       -4-

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Registered Holder's family, heirs, executors or legal representatives or trusts
for the benefit of such Registered Holder's family, or a transfer by a
Registered Holder which is a limited liability company to a member of such
limited liability company or a retired member or to the estate of any such
member or retired member, provided that the transferee in each case agrees in
writing to be subject to the terms of this Section 4, or (ii) a transfer made in
accordance with Rule 144 under the Act.

                  (c)      Each certificate representing Warrant Shares shall
bear a legend substantially in the following form:

                  "The securities represented by this
                  certificate have not been registered under
                  the Securities Act of 1933, as amended,
                  and may not be offered, sold or otherwise
                  transferred, pledged or hypothecated
                  unless and until such securities are
                  registered under such Act or an opinion of
                  counsel satisfactory to the Company is
                  obtained to the effect that such
                  registration is not required."

The foregoing legend shall be removed from the certificates representing any
Warrant Shares, at the request of the holder thereof, at such time as they
become eligible for resale pursuant to Rule 144(k) under the Act.

         5.       NO IMPAIRMENT. The Company will not, by amendment of its
charter or through any reorganization, transfer of assets, consolidation,
merger, dissolution, issue or sale of securities or any other voluntary action,
avoid or seek to avoid the observance or performance of any of the terms of this
Warrant, but will at all times in good faith assist in the carrying out of all
such terms and in the taking of all such action as may be necessary or
appropriate in order to protect the rights of the holder of this Warrant against
impairment.

         6.       NOTICES OF RECORD DATE, ETC. In the event:

                  (a)      the Company shall take a record of the holders of its
Common Stock (or other stock or securities at the time deliverable upon the
exercise of this Warrant) for the purpose of entitling or enabling them to
receive any dividend or other distribution, or to receive any right to subscribe
for or purchase any shares of stock of any class or any other securities, or to
receive any other right; or

                  (b)      of any capital reorganization of the Company, any
reclassification of the Common Stock of the Company, any consolidation or merger
of the Company with or into another corporation (other than a consolidation or
merger in which the Company is the surviving entity and its Common Stock is not
converted into or exchanged for any other securities or property), or any
transfer of all or substantially all of the assets of the Company; or

                  (c)      of the voluntary or involuntary dissolution,
liquidation or winding-up of the Company,

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then, and in each such case, the Company will mail or cause to be mailed to the
Registered Holder a notice specifying, as the case may be, (i) the record date
for such dividend, distribution or right, and the amount and character of such
dividend, distribution or right, or (ii) the effective
date on which such reorganization, reclassification, consolidation, merger,
transfer, dissolution, liquidation or winding-up is to take place, and the time,
if any is to be fixed, as of which the holders of record of Common Stock (or
such other stock or securities at the time deliverable upon the exercise of this
Warrant) shall be entitled to exchange their shares of Common Stock (or such
other stock or securities) for securities or other property deliverable upon
such reorganization, reclassification, consolidation, merger, transfer,
dissolution, liquidation or winding-up. Such notice shall be mailed at least ten
days prior to the record date or effective date for the event specified in such
notice.

         7.       RESERVATION OF STOCK. The Company will at all times reserve
and keep available, solely for issuance and delivery upon the exercise of this
Warrant, such number of Warrant Shares and other securities, cash and/or
property, as from time to time shall be issuable upon the exercise of this
Warrant.

         8.       EXCHANGE OF WARRANTS. Upon the surrender by the Registered
Holder, properly endorsed, to the Company at the principal office of the
Company, the Company will, subject to the provisions of Section 4 hereof, issue
and deliver to or upon the order of such Holder, at the Company's expense, a new
Warrant or Warrants of like tenor, in the name of the Registered Holder or as
the Registered Holder (upon payment by the Registered Holder of any applicable
transfer taxes) may direct, calling in the aggregate on the face or faces
thereof for the number of shares of Common Stock (or other securities, cash
and/or property) then issuable upon exercise of this Warrant.

         9.       REPLACEMENT OF WARRANTS. Upon receipt of evidence reasonably
satisfactory to the Company of the loss, theft, destruction or mutilation of
this Warrant and (in the case of loss, theft or destruction) upon delivery of an
indemnity agreement (with surety if reasonably required) in an amount reasonably
satisfactory to the Company, or (in the case of mutilation) upon surrender and
cancellation of this Warrant, the Company will issue, in lieu thereof, a new
Warrant of like tenor.

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         10.      TRANSFERS, ETC.

                  (a)      The Company will maintain a register containing the
name and address of the Registered Holder of this Warrant. The Registered Holder
may change its or his address as shown on the warrant register by written notice
to the Company requesting such change.

                  (b)      Subject to the provisions of Section 4 hereof, this
Warrant and all rights hereunder are transferable, in whole or in part, upon
surrender of this Warrant with a properly executed assignment (in the form of
EXHIBIT II hereto) at the principal office of the Company.

                  (c)      Until any transfer of this Warrant is made in the
warrant register, the Company may treat the Registered Holder as the absolute
owner hereof for all purposes; PROVIDED, HOWEVER, that if and when this Warrant
is properly assigned in blank, the Company may (but shall not be obligated to)
treat the bearer hereof as the absolute owner hereof for all purposes,
notwithstanding any notice to the contrary.

         11.      MAILING OF NOTICES, ETC. All notices and other communications
from the Company to the Registered Holder shall be mailed by first-class
certified or registered mail, postage prepaid, to the address last furnished to
the Company in writing by the Registered Holder. All notices and other
communications from the Registered Holder or in connection herewith to the
Company shall be mailed by first-class certified or registered mail, postage
prepaid, to the Company at its principal office set forth below. If the Company
should at any time change the location of its principal office to a place other
than as set forth below, it shall give prompt written notice to the Registered
Holder and thereafter all references in this Warrant to the location of its
principal office at the particular time shall be as so specified in such notice.

         12.      NO RIGHTS AS STOCKHOLDER. Until the exercise of this Warrant,
the Registered Holder shall not have or exercise any rights by virtue hereof as
a stockholder of the Company. Notwithstanding the foregoing, in the event (i)
the Company effects a split of the Common Stock by means of a stock dividend and
the Purchase Price of and the number of Warrant Shares are adjusted as of the
date of the distribution of the dividend (rather than as of the record date for
such dividend), and (ii) the Registered Holder exercises this Warrant between
the record date and the distribution date for such stock dividend, the
Registered Holder shall be entitled to receive, on the distribution date, the
stock dividend with respect to the shares of Common Stock acquired upon such
exercise, notwithstanding the fact that such shares were not outstanding as of
the close of business on the record date for such stock dividend.

         13.      CHANGE OR WAIVER. Changes in or additions to this Warrant may
be made or compliance with any term, covenant, agreement, condition or provision
set forth herein may be omitted or waived (either generally or in a particular
instance and either retroactively or prospectively), upon written consent of the
Company and the holders of at least 50% of the principal amount of the Warrants
then outstanding; PROVIDED, HOWEVER, that no change, addition, omission or
waiver which causes any change in or extension of the time of payment of the
principal amount or interest, or the reduction of the rate of interest on, or in
any way affects or impairs the obligation of the Company in respect of the
principal of or interest on, any Warrant,

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or causes any change in this Section 6(c), shall be made without the written
consent of the holder of such Warrant.

         14.      SECTION HEADINGS. The section headings in this Warrant are for
the convenience of the parties and in no way alter, modify, amend, limit or
restrict the contractual obligations of the parties.

         15.      GOVERNING LAW. This Warrant will be governed by and construed
in accordance with the internal laws of the Commonwealth of Massachusetts
(without reference to the conflicts of law provisions thereof).

         EXECUTED as of the Date of Issuance indicated above.

                                                The Medicines Company

         By:________________________________

         Title:_____________________________

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                                                                       EXHIBIT I

                                  EXERCISE FORM

To:_________________                                        Dated:____________

The undersigned, pursuant to the provisions set forth in the attached Warrant
(No. ___), hereby irrevocably elects to purchase (check applicable box):

       *      _____ shares of the Common Stock covered by such Warrant; or

       *      the maximum number of shares of Common Stock covered by such
              Warrant pursuant to the cashless exercise procedure set forth in
              Section 1(b).

The undersigned herewith makes payment of the full purchase price for such
shares at the price per share provided for in such Warrant, which is $________.
Such payment takes the form of (check applicable box or boxes):

       *      $______ in lawful money of the United States; and/or

       *      the cancellation of such portion of the attached Warrant as is
              exercisable for a total of _____ Warrant Shares (using a Fair
              Market Value of $_____ per share for purposes of this
              calculation); and/or

       *      the cancellation of such number of Warrant Shares as is necessary,
              in accordance with the formula set forth in Section 1(b), to
              exercise this Warrant with respect to the maximum number of
              Warrant Shares purchasable pursuant to the cashless exercise
              procedure set forth in Section 1(b).

       Signature:______________________

       Address: _______________________

_____________________

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                                                                      EXHIBIT II

                                 ASSIGNMENT FORM

FOR VALUE RECEIVED, ________________________________________ hereby sells,
assigns and transfers all of the rights of the undersigned under the attached
Warrant (No. ____) with respect to the number of shares of Common Stock covered
thereby set forth below, unto:

Name of Assignee                    Address                   No. of Shares
----------------                    -------                   -------------

Dated: __________________________    Signature: ________________________________

                                     -10-<PAGE>   1
                                                                   EXHIBIT 10.20

                     THIS WARRANT AND THE SHARES OF COMMON
                 STOCK ISSUED UPON ITS EXERCISE ARE SUBJECT TO
                   THE RESTRICTIONS ON TRANSFER SET FORTH IN
                           SECTION 4 OF THIS WARRANT

Warrant No. ____                                     Number of Shares: ________
                                                         (subject to adjustment)

Date of Issuance:  March 2, 2000

                              The Medicines Company

                          Common Stock Purchase Warrant

                          (Void after March 2, 2005)

The Medicines Company, a Delaware corporation (the "Company"), for value
received, hereby certifies that ___________________, or its registered assigns
(the "Registered Holder"), is entitled, subject to the terms and conditions set
forth below, to purchase from the Company, at any time or from time to time on
or after the date of issuance and on or before 5:00 p.m. (Boston time) on March
___, 2005, ________ shares of common stock, $0.001 par value per share (the
"Common Stock"), of the Company, at a purchase price of $4.32 per share. The
shares purchasable upon exercise of this Warrant, and the purchase price per
share, each as adjusted from time to time pursuant to the provisions of this
Warrant, are hereinafter referred to as the "Warrant Shares" and the "Purchase
Price," respectively.

This Warrant is being issued by the Company to the Registered Holder in
connection with the closing of the sale to the Registered Holder of an 8%
Convertible Note in the original principal amount of $________ and is one of a
series of common stock purchase warrants (the "Warrants") issued in connection
with the sale by the Company of 8% Convertible Notes in the aggregate original
principal amount of between a minimum of $12,000,000 and a maximum of
$15,000,000 (the "Notes").

         1.       EXERCISE.

                  (a)      This Warrant may be exercised by the Registered
   Holder, in whole or in part, by surrendering this Warrant, with the exercise
form appended hereto as Exhibit I duly executed by the Registered Holder or by
the Registered Holder's duly authorized attorney, at the principal office of the
Company, or at such other office or agency as the Company may designate,
accompanied by payment in full, in lawful money of the United States, of the
Purchase Price payable in respect of the number of Warrant Shares purchased upon
such exercise.

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                  (b)      The Registered Holder may, at its option, elect to
pay some or all of the Purchase Price payable upon an exercise of this Warrant
by canceling a portion of this Warrant exercisable for such number of Warrant
Shares as is determined by dividing (i) the total Purchase Price payable in
respect of the number of Warrant Shares being purchased upon such exercise by
(ii) the excess of the Fair Market Value per share of Common Stock (as defined
below) as of the Exercise Date (as defined in subsection 1(c) below) over the
Purchase Price per share. If the Registered Holder wishes to exercise this
Warrant pursuant to this method of payment with respect to the maximum number of
Warrant Shares purchasable pursuant to this method, then the number of Warrant
Shares so purchasable shall be equal to the total number of Warrant Shares,
minus the product obtained by multiplying (x) the total number of Warrant Shares
by (y) a fraction, the numerator of which shall be the Purchase Price per share
and the denominator of which shall be the Fair Market Value per share of Common
Stock as of the Exercise Date. The Fair Market Value per share of Common Stock
shall be determined as follows:

                           (i)      If the Common Stock is listed on a national
securities exchange, the Nasdaq National Market or another nationally recognized
trading system as of the Exercise Date, the Fair Market Value per share of
Common Stock shall be deemed to be the average of the high and low reported sale
prices per share of Common Stock thereon on the trading day immediately
preceding the Exercise Date (provided that if no such price is reported on such
day, the Fair Market Value per share of Common Stock shall be determined
pursuant to clause (ii)).

                           (ii)     If the Common Stock is not listed on a
national securities exchange, the Nasdaq National Market or another nationally
recognized trading system as of the Exercise Date, the Fair Market Value per
share of Common Stock shall be deemed to be the amount most recently determined
by the Board of Directors to represent the fair market value per share of the
Common Stock (including without limitation a determination for purposes of
granting Common Stock options or issuing Common Stock under an employee benefit
plan of the Company); and, upon request of the Registered Holder, the Board of
Directors (or a representative thereof) shall promptly notify the Registered
Holder of the Fair Market Value per share of Common Stock. Notwithstanding the
foregoing, if the Board of Directors has not made such a determination within
the three-month period prior to the Exercise Date, then (A) the Board of
Directors shall make a determination of the Fair Market Value per share of the
Common Stock within 15 days of a request by the Registered Holder that it do so,
and (B) the exercise of this Warrant pursuant to this subsection 1(b) shall be
delayed until such determination is made.

                  (c)      Each exercise of this Warrant shall be deemed to have
been effected immediately prior to the close of business on the day on which
this Warrant shall have been surrendered to the Company as provided in
subsection 1(a) above (the "Exercise Date"). At such time, the person or persons
in whose name or names any certificates for Warrant Shares shall be issuable
upon such exercise as provided in subsection 1(d) below shall be deemed to have
become the holder or holders of record of the Warrant Shares represented by such
certificates.

                  (d)      As soon as practicable after the exercise of this
Warrant in full or in part, and in any event within 10 days thereafter, the
Company, at its expense, will cause to be issued in the name of, and delivered
to, the Registered Holder, or as such Holder (upon payment by such Holder of any
applicable transfer taxes) may direct:

                                      -2-
<PAGE>   3

                           (i)      a certificate or certificates for the number
of full Warrant Shares to which the Registered Holder shall be entitled upon
such exercise plus, in lieu of any fractional share to which the Registered
Holder would otherwise be entitled, cash in an amount determined pursuant to
Section 3 hereof; and

                           (ii)     in case such exercise is in part only, a new
warrant or warrants (dated the date hereof) of like tenor, calling in the
aggregate on the face or faces thereof for the number of Warrant Shares equal
(without giving effect to any adjustment therein) to the number of such shares
called for on the face of this Warrant minus the sum of (a) the number of such
shares purchased by the Registered Holder upon such exercise plus (b) the number
of Warrant Shares (if any) covered by the portion of this Warrant canceled in
payment of the Purchase Price payable upon such exercise pursuant to subsection
1(b) above.

         2.       ADJUSTMENTS.

                  (a)      If the Company consummates an Investor Sale (as
defined in the Notes) for consideration per share (the "Investor Price") which
is less than the Purchase Price in effect immediately prior to such Investor
Sale, then, immediately upon, and only upon, the consummation of the first such
Investor Sale, the Purchase Price shall be adjusted to equal the Investor Price.
For purposes of this section consideration received by the Company shall be
computed as follows:

                           (i)      insofar as it consists of cash, be computed
at the aggregate of cash received by the Company, excluding amounts paid or
payable for accrued interest; and

                           (ii)     insofar as it consists of property other
than cash, be computed at the fair market value thereof at the time of such
issue, as determined in good faith by the Board of Directors; and

                           (iii)    if the shares in the Investor Sale are
issued together with other shares or securities or other assets of the Company
for consideration which covers both, be the proportion of such consideration so
received, computed as provided in clauses (I) and (II) above, as determined in
good faith by the Board of Directors.

                  (b)      If the Company consummates a Consensual Conversion
(as defined in the Notes) at a conversion price per share (the "Consensual
Conversion Price") which is less than the Purchase Price in effect immediately
prior to such Consensual Conversion, then the Purchase Price shall be adjusted
to equal the Consensual Conversion Price.

                  (c)      If outstanding shares of the Company's Common Stock
shall be subdivided into a greater number of shares or a dividend in Common
Stock shall be paid in respect of Common Stock, the Purchase Price in effect
immediately prior to such subdivision or at the record date of such dividend
shall simultaneously with the effectiveness of such subdivision or immediately
after the record date of such dividend be proportionately reduced. If
outstanding shares of Common Stock shall be combined into a smaller number of
shares, the Purchase Price in effect immediately prior to such combination
shall, simultaneously with the effectiveness of such combination, be
proportionately increased.

                                      -3-
<PAGE>   4

                  (d)      When any adjustment is required to be made in the
Purchase Price under this Section 2, the number of Warrant Shares purchasable
upon the exercise of this Warrant shall be changed to the number determined by
dividing (i) an amount equal to the number of Warrant Shares issuable upon the
exercise of this Warrant immediately prior to such adjustment, multiplied by the
Purchase Price in effect immediately prior to such adjustment, by (ii) the
Purchase Price in effect immediately after such adjustment.

                  (e)      If there shall occur any capital reorganization or
reclassification of the Company's Common Stock (other than a change in par value
or a subdivision or combination as provided for in subsection 2(c) above), or
any consolidation or merger of the Company with or into another corporation, or
a transfer of all or substantially all of the assets of the Company, then, as
part of any such reorganization, reclassification, consolidation, merger or
sale, as the case may be, lawful provision shall be made so that the Registered
Holder of this Warrant shall have the right thereafter to receive upon the
exercise hereof the kind and amount of shares of stock or other securities or
property which such Registered Holder would have been entitled to receive if,
immediately prior to any such reorganization, reclassification, consolidation,
merger or sale, as the case may be, such Registered Holder had held the number
of shares of Common Stock which were then purchasable upon the exercise of this
Warrant. In any such case, appropriate adjustment (as reasonably determined in
good faith by the Board of Directors of the Company) shall be made in the
application of the provisions set forth herein with respect to the rights and
interests thereafter of the Registered Holder of this Warrant, such that the
provisions set forth in this Section 2 (including provisions with respect to
adjustment of the Purchase Price) shall thereafter be applicable, as nearly as
is reasonably practicable, in relation to any shares of stock or other
securities or property thereafter deliverable upon the exercise of this Warrant.

                  (f)      When any adjustment is required to be made in the
Purchase Price, the Company shall promptly mail to the Registered Holder a
certificate setting forth the Purchase Price after such adjustment and setting
forth a brief statement of the facts requiring such adjustment. Such certificate
shall also set forth the kind and amount of stock or other securities or
property into which this Warrant shall be exercisable following the occurrence
of any of the events specified in this Section 2.

         3.       FRACTIONAL SHARES. The Company shall not be required upon the
exercise of this Warrant to issue any fractional shares, but shall make an
adjustment therefor in cash on the basis of the Fair Market Value per share of
Common Stock, as determined pursuant to subsection 1(b) above.

         4.       REQUIREMENTS FOR TRANSFER.

                  (a)      This Warrant and the Warrant Shares shall not be sold
or transferred unless either (i) they first shall have been registered under the
Securities Act of 1933, as amended (the "Act"), or (ii) the Company first shall
have been furnished with an opinion of legal counsel, reasonably satisfactory to
the Company, to the effect that such sale or transfer is exempt from the
registration requirements of the Act.

                  (b)      Notwithstanding the foregoing, no registration or
opinion of counsel shall be required for (i) a transfer by a Registered Holder
which is a corporation to a wholly owned

                                      -4-
<PAGE>   5

subsidiary of such corporation, a transfer by a Registered Holder which is a
partnership to a partner of such partnership or a retired partner of such
partnership or to the estate of any such partner or retired partner, a transfer
by a Registered Holder who is an individual to any members of such Registered
Holder's family, heirs, executors or legal representatives or trusts for the
benefit of such Registered Holder's family, or a transfer by a Registered Holder
which is a limited liability company to a member of such limited liability
company or a retired member or to the estate of any such member or retired
member, provided that the transferee in each case agrees in writing to be
subject to the terms of this Section 4, or (ii) a transfer made in accordance
with Rule 144 under the Act.

                  (c)      Each certificate representing Warrant Shares shall
bear a legend substantially in the following form:

                  "The securities represented by this
                  certificate have not been registered under
                  the Securities Act of 1933, as amended,
                  and may not be offered, sold or otherwise
                  transferred, pledged or hypothecated
                  unless and until such securities are
                  registered under such Act or an opinion of
                  counsel satisfactory to the Company is
                  obtained to the effect that such
                  registration is not required."

The foregoing legend shall be removed from the certificates representing any
Warrant Shares, at the request of the holder thereof, at such time as they
become eligible for resale pursuant to Rule 144(k) under the Act.

         5.       NO IMPAIRMENT. The Company will not, by amendment of its
charter or through any reorganization, transfer of assets, consolidation,
merger, dissolution, issue or sale of securities or any other voluntary action,
avoid or seek to avoid the observance or performance of any of the terms of this
Warrant, but will at all times in good faith assist in the carrying out of all
such terms and in the taking of all such action as may be necessary or
appropriate in order to protect the rights of the holder of this Warrant against
impairment.

         6.       NOTICES OF RECORD DATE, ETC. In the event:

                  (a)      the Company shall take a record of the holders of its
Common Stock (or other stock or securities at the time deliverable upon the
exercise of this Warrant) for the purpose of entitling or enabling them to
receive any dividend or other distribution, or to receive any right to subscribe
for or purchase any shares of stock of any class or any other securities, or to
receive any other right; or

                  (b)      of any capital reorganization of the Company, any
reclassification of the Common Stock of the Company, any consolidation or merger
of the Company with or into another corporation (other than a consolidation or
merger in which the Company is the surviving entity and its Common Stock is not
converted into or exchanged for any other securities or property), or any
transfer of all or substantially all of the assets of the Company; or

                  (c)      of the voluntary or involuntary dissolution,
liquidation or winding-up of the Company,

                                      -5-
<PAGE>   6

then, and in each such case, the Company will mail or cause to be mailed to the
Registered Holder a notice specifying, as the case may be, (i) the record date
for such dividend, distribution or right, and the amount and character of such
dividend, distribution or right, or (ii) the effective date on which such
reorganization, reclassification, consolidation, merger, transfer, dissolution,
liquidation or winding-up is to take place, and the time, if any is to be fixed,
as of which the holders of record of Common Stock (or such other stock or
securities at the time deliverable upon the exercise of this Warrant) shall be
entitled to exchange their shares of Common Stock (or such other stock or
securities) for securities or other property deliverable upon such
reorganization, reclassification, consolidation, merger, transfer, dissolution,
liquidation or winding-up. Such notice shall be mailed at least ten days prior
to the record date or effective date for the event specified in such notice.

         7.       RESERVATION OF STOCK. The Company will at all times reserve
and keep available, solely for issuance and delivery upon the exercise of this
Warrant, such number of Warrant Shares and other securities, cash and/or
property, as from time to time shall be issuable upon the exercise of this
Warrant.

         8.       EXCHANGE OF WARRANTS. Upon the surrender by the Registered
Holder, properly endorsed, to the Company at the principal office of the
Company, the Company will, subject to the provisions of Section 4 hereof, issue
and deliver to or upon the order of such Holder, at the Company's expense, a new
Warrant or Warrants of like tenor, in the name of the Registered Holder or as
the Registered Holder (upon payment by the Registered Holder of any applicable
transfer taxes) may direct, calling in the aggregate on the face or faces
thereof for the number of shares of Common Stock (or other securities, cash
and/or property) then issuable upon exercise of this Warrant.

         9.       REPLACEMENT OF WARRANTS. Upon receipt of evidence reasonably
satisfactory to the Company of the loss, theft, destruction or mutilation of
this Warrant and (in the case of loss, theft or destruction) upon delivery of an
indemnity agreement (with surety if reasonably required) in an amount reasonably
satisfactory to the Company, or (in the case of mutilation) upon surrender and
cancellation of this Warrant, the Company will issue, in lieu thereof, a new
Warrant of like tenor.

         10.      TRANSFERS, ETC.

                  (a)      The Company will maintain a register containing the
name and address of the Registered Holder of this Warrant. The Registered Holder
may change its or his address as shown on the warrant register by written notice
to the Company requesting such change.

                  (b)      Subject to the provisions of Section 4 hereof, this
Warrant and all rights hereunder are transferable, in whole or in part, upon
surrender of this Warrant with a properly executed assignment (in the form of
EXHIBIT II hereto) at the principal office of the Company.

                  (c)      Until any transfer of this Warrant is made in the
warrant register, the Company may treat the Registered Holder as the absolute
owner hereof for all purposes; PROVIDED, HOWEVER, that if and when this Warrant
is properly assigned in blank, the Company may (but shall not be obligated to)
treat the bearer hereof as the absolute owner hereof for all

                                      -6-
<PAGE>   7
purposes, notwithstanding any notice to the contrary.

         11.      MAILING OF NOTICES, ETC. All notices and other communications
from the Company to the Registered Holder shall be mailed by first-class
certified or registered mail, postage prepaid, to the address last furnished to
the Company in writing by the Registered Holder. All notices and other
communications from the Registered Holder or in connection herewith to the
Company shall be mailed by first-class certified or registered mail, postage
prepaid, to the Company at its principal office set forth below. If the Company
should at any time change the location of its principal office to a place other
than as set forth below, it shall give prompt written notice to the Registered
Holder and thereafter all references in this Warrant to the location of its
principal office at the particular time shall be as so specified in such notice.

         12.      NO RIGHTS AS STOCKHOLDER. Until the exercise of this Warrant,
the Registered Holder shall not have or exercise any rights by virtue hereof as
a stockholder of the Company. Notwithstanding the foregoing, in the event (i)
the Company effects a split of the Common Stock by means of a stock dividend and
the Purchase Price of and the number of Warrant Shares are adjusted as of the
date of the distribution of the dividend (rather than as of the record date for
such dividend), and (ii) the Registered Holder exercises this Warrant between
the record date and the distribution date for such stock dividend, the
Registered Holder shall be entitled to receive, on the distribution date, the
stock dividend with respect to the shares of Common Stock acquired upon such
exercise, notwithstanding the fact that such shares were not outstanding as of
the close of business on the record date for such stock dividend.

         13.      CHANGE OR WAIVER. Changes in or additions to this Warrant may
be made or compliance with any term, covenant, agreement, condition or provision
set forth herein may be omitted or waived (either generally or in a particular
instance and either retroactively or prospectively), upon written consent of the
Company and the holders of at least 50% of the shares of capital stock issued or
then issuable upon exercise of the Warrants then outstanding; PROVIDED, HOWEVER,
that any such amendment or waiver must apply to all warrants then outstanding;
and provided further that the number of Warrant Shares subject to this Warrant
and the Purchase Price of this Warrant may not be amended, and the right to
exercise this Warrant may not be waived, without the written consent of the
holder of this Warrant (it being agreed that an amendment to or waiver under any
of the provisions of Section 2 of this Warrant shall not be considered an
amendment of the number of Warrant Shares or the Purchase Price).

         14.      SECTION HEADINGS. The section headings in this Warrant are for
the convenience of the parties and in no way alter, modify, amend, limit or
restrict the contractual obligations of the parties.

         15.      GOVERNING LAW. This Warrant will be governed by and construed
in accordance with the internal laws of the Commonwealth of Massachusetts
(without reference to the conflicts of law provisions thereof).

                                      -7-

<PAGE>   8

         EXECUTED as of the Date of Issuance indicated above.

                                        The Medicines Company

                                        By: ______________________________
                                        Title:  Chief Financial Officer

                                      -8-

<PAGE>   9
                                                                       EXHIBIT I

                                  EXERCISE FORM

To:_________________                                     Dated:____________

The undersigned, pursuant to the provisions set forth in the attached Warrant
(No. ___), hereby irrevocably elects to purchase (check applicable box):

                  _____ shares of the Common Stock covered by such Warrant; or

                  the maximum number of shares of Common Stock covered by such
                  Warrant pursuant to the cashless exercise procedure set forth
                  in Section 1(b).

The undersigned herewith makes payment of the full purchase price for such
shares at the price per share provided for in such Warrant, which is $________.
Such payment takes the form of (check applicable box or boxes):

                  $______ in lawful money of the United States; and/or

                  the cancellation of such portion of the attached Warrant as is
                  exercisable for a total of _____ Warrant Shares (using a Fair
                  Market Value of $_____ per share for purposes of this
                  calculation); and/or

                  the cancellation of such number of Warrant Shares as is
                  necessary, in accordance with the formula set forth in Section
                  1(b), to exercise this Warrant with respect to the maximum
                  number of Warrant Shares purchasable pursuant to the cashless
                  exercise procedure set forth in Section 1(b).

                                                Signature: ____________________

                                                Address: ______________________

                                                         ______________________

                                       -9-

<PAGE>   10

                                                                      EXHIBIT II

                                ASSIGNMENT FORM

FOR VALUE RECEIVED, ________________________________________ hereby sells,
assigns and transfers all of the rights of the undersigned under the attached
Warrant (No. ____) with respect to the number of shares of Common Stock covered
thereby set forth below, unto:

Name of Assignee                    Address                   No. of Shares
----------------                    -------                   -------------

Dated: _________________________     Signature: ________________________________

                                      -10-

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