EXHIBIT 5.1


July 31, 2003



LEHMAN BROTHERS INC.,
Citigroup Global Markets Inc.
Needham & Company, Inc.
U.S. Bancorp Piper Jaffray Inc.
SG Cowen Securities Corporation
c/o Lehman Brothers Inc.
745 Seventh Avenue
New York, New York  10019


Re:     Public Offering of 4,600,000 Shares of Common Stock of Esperion
        Therapeutics, Inc.

Dear Sir or Madam:

We have acted as counsel to Esperion Therapeutics, Inc., a Delaware corporation
(the "Company"), in connection with the preparation of the subject registration
statement on Form S-3 (as such may be amended or supplemented, the "Registration
Statement"), filed with the Securities and Exchange Commission pursuant to the
Securities Act of 1933, as amended (the "Act"), to register up to 4,600,000
shares (the "Shares") of Common Stock, par value $0.001 per share (the "Common
Stock") to be sold in a public offering (the "Offering"), including 434,000
shares of Common Stock to be sold by the Company and 166,000 shares of Common
Stock to be sold by certain selling stockholders pursuant to an over-allotment
option granted to the Underwriters. All of the shares to be sold by the Company
are authorized but heretofore unissued.

In rendering the opinion set forth below, we have reviewed (a) the Registration
Statement; (b) the Company's Certificate of Incorporation, as amended to date;
(c) the Company's Bylaws, as amended to date; (d) certain records of the
Company's corporate proceedings as reflected in its minute and stock books; (e)
the Form of Underwriting Agreement filed as Exhibit 1.1 to the Registration
Statement (the "Underwriting Agreement"), to be executed by the Company, certain
selling stockholders and Lehman Brothers Inc., Citigroup Global Markets Inc.,
Needham & Company, Inc., U.S. Bancorp Piper Jaffray Inc. and SG Cowen Securities
Corporation (together, the "Underwriters"); and (f) such records, documents,
statutes and decisions as we have deemed relevant. In our examination, we have
assumed the genuineness of all signatures, the authenticity of



July 31, 2003
Page 2



all documents submitted to us as originals and the conformity with the original
of all documents submitted to us as copies thereof.

Based upon the foregoing, and in reliance thereon, we are of the opinion that
the Shares to be sold by the Company as described in the Registration Statement,
when and to the extent purchased by the Underwriters in accordance with the
Underwriting Agreement, will be validly issued, fully paid and nonassessable.

We hereby consent to the use of this opinion as Exhibit 5.1 to the Registration
Statement and further consent to the use of our name wherever appearing in the
Registration Statement, including the prospectus constituting a part thereof,
and any amendment thereto. In giving such opinion and consent, we do not thereby
admit that we are acting within the category of persons whose consent is
required under Section 7 of the Act or the rules or regulations of the
Securities and Exchange Commission promulgated thereunder.


Very truly yours,

/s/ Morgan, Lewis & Bockius LLP