<PAGE>
                                                                     Exhibit 4.1

                        [Form of common stock certificate
                        of Medco Health Solutions, Inc.]

Number                                                                    SHARES

                           Medco Health Solutions, Inc.
              INCORPORATED UNDER THE LAWS OF THE STATE OF DELAWARE

MHS

                                  COMMON STOCK

                                                               CUSIP 58405U 10 2
                                                               SEE REVERSE FOR
                                                             CERTAIN DEFINITIONS

This certifies that


is the owner of

     FULLY PAID AND NON-ASSESSABLE SHARES OF THE COMMON STOCK OF THE PAR VALUE
OF ONE CENT ($0.01) EACH OF
========================Medco Health Solutions, Inc.============================
transferable on the books of the Corporation by the holder hereof in person or
by duly authorized attorney upon surrender of this certificate properly
endorsed. This certificate and the shares represented hereby are issued and
shall be held subject to all the provisions of the Certificate of Incorporation
of Medco Health Solutions, Inc., and to any and all amendments thereto, to all
of which the holder by acceptance hereof assents. This certificate is not valid
until countersigned by the Transfer Agent and registered by the registrar.

     WITNESS the facsimile seal of the Corporation and the facsimile signature
of its proper officers.

Dated:

<TABLE>
<S>                                                 <C>
                                                    /s/ David B. Snow, Jr.
                                                    CHAIRMAN, PRESIDENT AND
                                                    CHIEF EXECUTIVE OFFICER

                  [MEDCO HEALTH SOLUTIONS, INC. CORPORATE SEAL]

COUNTERSIGNED AND REGISTERED:
THE BANK of NEW YORK
                      TRANSFER AGENT
                       AND REGISTRAR
BY
   /s/ John D. Sivertsen                            /s/ David S. Machlowitz
   AUTHORIZED SIGNATURE                             SENIOR VICE PRESIDENT, GENERAL COUNSEL
                                                    AND SECRETARY
</TABLE>

<PAGE>

  [Form of reverse of Common Stock Certificate of Medco Health Solutions, Inc.]

                          Medco Health Solutions, Inc.

        The corporation will furnish without charge to each stockholder who so
requests the powers, designations, preferences and relative, participating,
optional, or other special rights of each class of stock or series thereof and
the qualifications, limitations or restrictions of such preferences and/or
rights. Such requests may be made to the corporation or the transfer agent.

   The following abbreviations, when used in the inscription on the face of this
certificate, shall be construed as though they were written out in full
according to applicable laws or regulations:

<TABLE>
<S>                                          <C>
TEN COM - as tenants in common               UNIF TRANS MIN ACT - ___________ Custodian____________
                                                                  (Cust)              (Minor)
TEN ENT - as tenants by the entireties                            under Uniform Transfers to Minors

JT TEN  - as joint tenants with right                             Act______________________________
          of survivorship and not as                                          (State)
          tenants in common
</TABLE>

     Additional abbreviations may also be used though not in the above list



   For value received, ___________________ hereby sell, assign and transfer unto


 PLEASE INSERT SOCIAL SECURITY OR OTHER
    IDENTIFYING NUMBER OF ASSIGNEE

[___________________________________]___________________________________________


________________________________________________________________________________
  (PLEASE PRINT OR TYPEWRITE NAME AND ADDRESS, INCLUDING ZIP CODE, OF ASSIGNEE)

________________________________________________________________________________


________________________________________________________________________________


_________________________________________________________________________ Shares
of the capital stock represented by the within Certificate, and do hereby
irrevocably constitute and appoint


_______________________________________________________________________ Attorney
to transfer the said stock on the books of the within named Corporation with
full power of substitution in the premises.


Dated____________________________


                       _________________________________________________________
                       NOTICE: THE SIGNATURE TO THIS ASSIGNMENT MUST CORRESPOND
                               WITH THE NAME AS WRITTEN UPON THE FACE OF THE
                               CERTIFICATE IN EVERY PARTICULAR WITHOUT
                               ALTERATION OR ENLARGEMENT OR ANY CHANGE WHATEVER.


Signatures(s) Guaranteed:


_______________________________________________________
THE SIGNATURE(S) SHOULD BE GUARANTEED BY AN ELIGIBLE
GUARANTOR INSTITUTION (BANKS, STOCKBROKERS, SAVINGS AND
LOAN ASSOCIATIONS AND CREDIT UNIONS WITH MEMBERSHIP IN
AN APPROVED SIGNATURE GUARANTEE MEDALLION PROGRAM),
PURSUANT TO S.E.C. RULE 17AD-15.
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