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                                                                     EXHIBIT 5.1


                         STRADLING YOCCA CARLSON & RAUTH
                           A PROFESSIONAL CORPORATION
                                ATTORNEYS AT LAW
                      660 NEWPORT CENTER DRIVE, SUITE 1600
                         NEWPORT BEACH, CALIFORNIA 92660

                            TELEPHONE (949) 725-4000
                               FAX (949) 725-4100



                                  May 18, 1999

NeoTherapeutics, Inc.
157 Technology Drive
Irvine, California 92618

        Re: Registration Statement on Form S-3

Ladies and Gentlemen:

        At your request, we have examined the form of Registration Statement on
Form S-3, Commission File No. 333-73009 (the "Registration Statement"), filed by
NeoTherapeutics, Inc., a Delaware corporation (the "Company"), with the
Securities and Exchange Commission in connection with the registration under the
Securities Act of 1933 for resale of an aggregate of up to 800,569 shares (the
"Shares") of Common Stock, par value $.001 per share, of the Company (the
"Common Stock"). The shares being registered for resale include: (i) 725,569
shares of Common Stock (the "Conversion Shares"), which may be issued upon
conversion of the shares of Series A Preferred Stock which were sold to two
investors pursuant to a Preferred Stock Purchase Agreement dated January 29,
1999 (the "Series A Purchase Agreement") between the Company and the selling
stockholders named in the Registration Statement (the "Selling Stockholders")
and (ii) 75,000 shares of Common Stock which are issuable upon exercise of
currently outstanding warrants (the "Warrants") issued to the Selling
Stockholders. The Shares may be sold from time to time for the account of the
Selling Stockholders.

        We have examined the proceedings heretofore taken by the Company in
connection with the authorization, issuance and sale of the securities referred
to above.

        Based on the foregoing, and assuming that the full consideration for
each share issuable upon exercise of the Warrants is received by the Company in
accordance with the terms of the Warrants, it is our opinion that the Shares
covered by the Registration Statement will, when issued, be validly issued and
outstanding, fully paid and nonassessable.

        We consent to the use of this opinion as an exhibit to the Registration
Statement and to the use of our name under the caption "Legal Matters" in the
Prospectus which is part of the Registration Statement.


                                        Very truly yours,

                                        /s/ STRADLING YOCCA CARLSON & RAUTH