EXHIBIT 32.1

                CERTIFICATION PURSUANT TO 18 U.S.C. SECTION 1350,

                             AS ADOPTED PURSUANT TO

                  SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

         In connection with the Quarterly Report on Form 10-Q of The Medicines
Company (the "Company") for the period ended September 30, 2003 as filed with
the Securities and Exchange Commission on the date hereof (the "Report"), I,
Clive A. Meanwell, M.D., Executive Chairman of the Company, hereby certify,
pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the
Sarbanes-Oxley Act of 2002, that:

         (1)      The Report fully complies with the requirements of Section
                  13(a) or 15(d) of the Securities Exchange Act of 1934; and

         (2)      The information contained in the Report fairly presents, in
                  all material respects, the financial condition and results of
                  operations of the Company.

                                   BY: /s/ CLIVE A. MEANWELL, M.D.
                                      -----------------------------

  Dated: November 6, 2003          Clive A. Meanwell, M.D.
                                   Executive Chairman

         A signed original of this written statement required by Section 906 has
been provided to The Medicines Company and will be retained by The Medicines
Company and furnished to the SEC or its staff upon request