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                                                                    EXHIBIT 4.5



         THIS CERTIFICATE IS NOT TRANSFERABLE TO ANY PERSON, EXCEPT THAT THE
HOLDER AND ANY WHOLLY-OWNED SUBSIDIARY MAY TRANSFER THIS SECURITY TO CAREMARK
RX, INC. OR A WHOLLY-OWNED SUBSIDIARY OF CAREMARK RX, INC. OR ANY ENTITY OWNING
ALL OF THE OUTSTANDING COMMON STOCK OF CAREMARK RX, INC., SUBJECT TO RECEIPT BY
THE TRUST OF AN OPINION OF COUNSEL THAT SUCH TRANSFER WOULD NOT CAUSE MORE THAN
AN INSUBSTANTIAL RISK THAT (I) THE TRUST WOULD NOT BE CLASSIFIED FOR UNITED
STATES FEDERAL INCOME TAX PURPOSES AS A GRANTOR TRUST; OR (II) THE TRUST WOULD
BE AN INVESTMENT COMPANY REQUIRED TO REGISTER UNDER THE INVESTMENT COMPANY ACT
OR THE TRANSFEREE WOULD BECOME AN INVESTMENT COMPANY REQUIRED TO REGISTER UNDER
THE INVESTMENT COMPANY ACT.


      CERTIFICATE NUMBER:                      NUMBER OF COMMON SECURITIES:

            C-1                                        123,720


                  Certificate Evidencing Common Securities of
                          CAREMARK RX CAPITAL TRUST I
                  (Liquidation Amount $50 per Common Security)

                  Caremark Rx Capital Trust I, a statutory business trust
created under the laws of the State of Delaware (the "Trust"), hereby certifies
that Caremark Rx, Inc. (the "Holder") is the registered owner of 123,720 common
securities of the Trust representing beneficial ownership interests of the
Trust and designated the Common Securities (Liquidation Amount $50 per Common
Security) (the "Common Securities"). In accordance with Section 5.11 of the
Trust Agreement (as defined below) the Common Securities are not transferable
except in limited circumstances and any attempted transfer, except in such
limited circumstances, shall be void. The designations, rights, privileges,
restrictions, preferences and other terms and provisions of the Common
Securities are set forth in, and this certificate and the Common Securities
represented hereby are issued and shall in all respects be subject to the terms
and provisions of, the Amended and Restated Trust Agreement of the Trust dated
as of September 29, 1999, as the same may be amended from time to time (the
"Trust Agreement") including the designation of the terms of the Common
Securities as set forth therein. The Trust will furnish a copy of the Trust
Agreement to the Holder without charge upon written request to the Trust at its
principal place of business or registered office.

                  Upon receipt of this certificate, the Holder is bound by the
Trust Agreement and is entitled to the benefits thereunder and by acceptance
hereof agrees to the provisions of (i) the Guarantee Agreement entered into by
Caremark Rx, Inc., a Delaware corporation ("Caremark"), and Wilmington Trust
Company, a Delaware banking corporation, as guarantee trustee, dated as of
September 29, 1999, and (ii) the Indenture entered into by Caremark and
Wilmington Trust Company, as trustee, dated as of September 29, 1999.
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                  This Certificate shall be construed in accordance with and
governed by the laws of the State of Delaware (without regard to conflict of
laws principles).
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                  IN WITNESS WHEREOF, one of the Administrative Trustees of the
Trust has executed this certificate.

                                   CAREMARK RX CAPITAL TRUST I



                                   By: /s/ James H. Dickerson, Jr.
                                       ---------------------------------------
                                       Name: James H. Dickerson, Jr.
                                       Title: Administrative Trustee