EXHIBIT 99.2


                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 March 31, 2003 as filed with the
Securities and Exchange Commission on the date hereof (the "Report"), I, David
M. Stack, Chief Executive Officer 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/ DAVID M. STACK
                                                   -----------------------------

      Dated: May 13, 2003                          David M. Stack
                                                   Chief Executive Officer

      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