Exhibit 4.2



 


SPECIMEN CLASS A ORDINARY SHARE CERTIFICATE


 





	NUMBER

DEFINITIONS	 	SHARES
	 	 	CUSIP [ ]


 


MSD
Acquisition Corp.

INCORPORATED UNDER THE LAWS OF THE CAYMAN ISLANDS

CLASS A ORDINARY SHARES


 


SEE REVERSE FOR

CERTAIN DEFINITIONS

CUSIP [ ]


 


This Certifies that                
is the owner of                 


 


FULLY PAID AND NON-ASSESSABLE CLASS A
ORDINARY SHARES

OF THE PAR VALUE OF US $0.0001 EACH OF

MSD Acquisition CoRP. (THE “COMPANY”)


 


subject to the Company’s amended
and restated memorandum and articles of association, as the same may be

amended from time to time, and transferable on the books
of the Company in person or by duly authorized attorney

upon surrender of this certificate properly endorsed.


 


The Company will be forced to redeem
all of its Class A ordinary shares if it is unable to complete a business

combination within the period set forth in the Company’s
amended and restated memorandum and articles of 

association, as the same may be amended from time to time, all as more fully described
in the Company’s final

prospectus dated February       , 2021.


 


This certificate is not valid unless
countersigned by the Transfer Agent

and registered by the Registrar.


 


Witness the facsimile signatures of its
duly authorized officers.


 


Witness the facsimile
signatures of its duly authorized officers.


 





	Dated:	 	 


 


 





	 	 		 
	Chief Executive Officer	Cayman Islands	 	Chief Financial Officer


 




     


     


    

 


MSD
Acquisition Corp.


 


The Company will furnish without charge
to each shareholder who so requests the powers, designations, preferences and relative, participating, optional or other special
rights of each class of shares or series thereof of the Company and the qualifications, limitations, or restrictions of such preferences
and/or rights. This certificate and the shares represented thereby are issued and shall be held subject to all the provisions of
the Company’s amended and restated memorandum and articles of association, as the same may be amended from time to time,
and resolutions of the Board of Directors providing for the issue of Class A ordinary shares (copies of which may be obtained from
the secretary of the Company), to all of which the holder of this certificate by acceptance hereof assents. 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:


 








	TEN
    COM	—	as
    tenants in common	 	 	 	 	Custodian	 
	 	 	 	 	 	 	(Cust)	 	(Minor)
	 	 	 	 	 	 	 	 	 
	TEN
    ENT-	—	as
    tenants by the entireties	 	 	 		 	
	 	 	 	 	 	 	 	(State)	 
	JT
    TEN-	—	as
    joint tenants with right of survivorship and not as tenants in common	 	 	
	 	 	 	 	 	 
	UNIF
    GIFT

    MIN ACT	—	under
    Uniform Gifts to Minors Act	 	 	 
	 	 	Additional
    abbreviations may also be used though not in the above list.	 	 	 


 




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For value received,                
hereby sells, assigns and transfers unto


 


(PLEASE INSERT SOCIAL SECURITY OR OTHER

IDENTIFYING NUMBER(S) OF ASSIGNEE(S))


 


(PLEASE PRINT OR TYPEWRITE NAME(S) AND ADDRESS(ES),

INCLUDING ZIP CODE, OF ASSIGNEE(S))


 


Shares represented
by the within Certificate, and does hereby irrevocably constitute and appoint                
Attorney to transfer the said shares on the books of the within named Company with full power of substitution in the premises.


 


 





	Dated	 	 	 
	 	 	 	Shareholder
	 	 	 	 
		 	 	NOTICE: THE SIGNATURE(S) 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.


 


Signature(s) Guaranteed:


 






	By:	     	 
	 	 
	 	 
	THE SIGNATURE(S) MUST 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 OR ANY SUCCESSOR RULES).	 


 


In each case, as more fully described in
the Company’s final prospectus dated        , 2021, the holder(s) of this certificate
shall be entitled to receive a pro-rata portion of certain funds held in the trust account established in connection with its initial
public offering only in the event that (i) the Company redeems the Class A ordinary shares sold in its initial public offering
and liquidates because it does not consummate an initial business combination within the period of time set forth in the Company’s
amended and restated memorandum and articles of association, as the same may be amended from time to time, (ii) the Company redeems
the Class A ordinary shares sold in its initial public offering in connection with a shareholder vote to amend the Company’s
amended and restated memorandum and articles of association (A) to modify the substance or timing of the Company’s obligation
to provide holders of the Class A ordinary shares the right to have their shares redeemed in connection with the Company’s
initial business combination or to redeem 100% of the Class A ordinary shares if the Company does not complete its initial business
combination within the time period set forth therein or (B) with respect to any other provision relating to the rights of holders
of the Class A ordinary shares or pre-initial business combination activity, or (iii) if the holder(s) seek(s) to redeem for cash
his, her, its or their respective Class A ordinary shares in connection with a tender offer (or proxy solicitation, solely in the
event the Company seeks shareholder approval of the proposed initial business combination) setting forth the details of a proposed
initial business combination. In no other circumstances shall the holder(s) have any right or interest of any kind in or to the
trust account.


 



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