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 Annual Report on Form 10-K/A of The Medicines Company
(the "Company") for the period ended December 31, 2002 as filed with the
Securities and Exchange Commission on the date hereof (the "Report"), the
undersigned, David M. Stack, President and Chief Executive Officer of the
Company, hereby certifies, pursuant to 18 U.S.C. Section 1350, that:


     (1)  The Report fully complies with the requirements of Section 13(a) of
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.



                                          /s/ David M. Stack
                                          ----------------------------
Dated:    March 7, 2003                   David M. Stack
                                          President and Chief Executive Officer