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                                                                     EXHIBIT 5.1

                          [LATHAM & WATKINS LETTERHEAD]


                                  June 6, 2000


NeoTherapeutics, Inc.
157 Technology Drive
Irvine, California 92612

     Re:  Registration of 660,000 shares of common stock, par value $.001 per
          share, of NeoTherapeutics, Inc., pursuant to a Registration Statement
          on Form S-3

Ladies and Gentlemen:

     In connection with the registration for resale of 660,000 shares of common
stock, par value $.001 per share of NeoTherapeutics, Inc., a Delaware
corporation (the "Company"), under the Securities Act of 1933, as amended, on
Form S-3 (the "Registration Statement"), you have requested our opinion with
respect to the matters set forth below. The shares being registered for resale
include: (i) 500,000 shares of common stock which were sold to Royal Canadian
Growth Fund (the "Investor") on May 1, 2000 (the "Shares"); (ii) 125,000 shares
of common stock which are currently issuable upon exercise of outstanding
warrants issued to the Investor on May 1, 2000 (the "Closing Warrants"); and
(iii) 35,000 shares of common stock which are currently issuable upon exercise
of finder's warrants issued to Dlouhy Investments Inc. on May 1, 2000 (the
"Finder's Warrants") (the Closing Warrants and Finder's Warrants are referred to
herein collectively as the "Warrants").

     We have made such legal and factual examinations and inquiries, including
an examination of originals or copies certified or otherwise identified to our
satisfaction of such documents, corporate records and instruments, as we have
deemed necessary or appropriate for purposes of this opinion.


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NeoTherapeutics, Inc.
June 6, 2000
Page 2

     In our examination, we have assumed the genuineness of all signatures, the
authenticity of all documents submitted to us as originals, and the conformity
to authentic original documents of all documents submitted to us as copies.

     We are opining herein as to the effect on the subject transaction only of
the General Corporation Law of the State of Delaware (including statutory and
reported decisional law), and we express no opinion with respect to the
applicability thereto, or the effect thereon, of the laws of any other
jurisdiction or, in the case of Delaware, any other laws, or as to any matters
of municipal law or the laws of any other local agencies within the state.

     Subject to the foregoing, it is our opinion that the Shares are, 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, the shares of common stock issuable upon exercise of the Warrants,
when issued, will be, validly issued, fully paid and nonassessable securities of
the Company.

     This opinion is rendered only to the Company and is solely for the benefit
of the Company in connection with the transaction covered hereby. This opinion
may not be relied upon by you for any other purpose, or furnished to, quoted to
or relied upon, by any other person, firm or corporation for any purpose,
without our prior written consent.

     We consent to your filing this opinion as an exhibit to the Registration
Statement and to the reference to our firm contained under the heading "Legal
Matters."


                                        Very truly yours,


                                        /s/ Latham & Watkins