<PAGE>

                                                                     EXHIBIT 4.1


NEITHER THESE SECURITIES NOR THE SECURITIES INTO WHICH THESE SECURITIES ARE
EXERCISABLE HAVE BEEN REGISTERED WITH THE SECURITIES AND EXCHANGE COMMISSION OR
THE SECURITIES COMMISSION OF ANY STATE IN RELIANCE UPON AN EXEMPTION FROM
REGISTRATION UNDER SECURITIES ACT OF 1933, AS AMENDED (THE "SECURITIES ACT"),
AND, ACCORDINGLY, MAY NOT BE OFFERED OR SOLD EXCEPT PURSUANT TO AN EFFECTIVE
REGISTRATION STATEMENT UNDER THE SECURITIES ACT OR PURSUANT TO AN AVAILABLE
EXEMPTION FROM THE REGISTRATION REQUIREMENTS THEREUNDER AND IN COMPLIANCE WITH
APPLICABLE STATE SECURITIES OR BLUE SKY LAWS.


                              NEOTHERAPEUTICS, INC.

                                     WARRANT

                            Dated: December 15, 1999


     NeoTherapeutics, Inc., a Delaware corporation (the "Company"), hereby
certifies that, for value received, ________________, or his/her registered
assigns ("Holder"), is entitled, subject to the terms set forth below, to
purchase from the Company up to a total of __________ shares of Common Stock,
$.001 par value per share (the "Common Stock"), of the Company (each such share,
a "Warrant Share" and all such shares, the "Warrant Shares") at an exercise
price equal to $13.00 per share (as adjusted from time to time as provided in
Section 8, the "Exercise Price"), at any time and from time to time from and
after the date hereof and through and including the earlier of (i) December 15,
2002 or (ii) the business day preceding a Redemption Date, as defined in Section
4 hereof (as applicable, the "Expiration Date"), and subject to the following
terms and conditions:

     1. Registration of Warrant. The Company shall register this Warrant upon
records to be maintained by the Company for that purpose (the "Warrant
Register"), in the name of the record Holder hereof from time to time. The
Company may deem and treat the registered Holder of this Warrant as the absolute
owner hereof for the purpose of any exercise hereof or any distribution to the
Holder, and for all other purposes, and the Company shall not be affected by
notice to the contrary.

     2. Registration of Transfers and Exchanges.

         (a) This Warrant or the Warrant Shares issued upon any exercise hereof
may only be transferred pursuant to an effective registration statement under
the Securities Act, to the Company or pursuant to an available exemption from or
in a transaction not subject to the registration requirements of the Securities
Act. In connection with any transfer of this Warrant or any Warrant Shares other
than pursuant to an effective registration statement or to the Company, the
Company may require the transferor thereof to provide to the Company an opinion
of counsel selected by the transferor, the form and substance of which opinion
shall be reasonably satisfactory to the Company, to the effect that such
transfer does not require registration of such transferred securities under the
Securities Act. Holder agrees to the imprinting, so long as is required by this
Section 2(a), of a legend substantially similar to that first above written on
any New Warrant (as defined in Section 2(b) below) or a legend of similar import
on any Warrant Shares issued upon an

<PAGE>

exercise hereof. Any such transferee shall agree in writing to be bound by the
terms of this Warrant and shall have the rights of Holder under this Warrant.

         (b) The Company shall register the transfer of any portion of this
Warrant in conformance with Section 2(a) in the Warrant Register, upon surrender
of this Warrant, with the Form of Assignment attached hereto duly completed and
signed, to the Company at the office specified in or pursuant to Section 11.
Upon any such registration or transfer, a new warrant to purchase Common Stock,
in substantially the form of this Warrant (any such new warrant, a "New
Warrant"), evidencing the portion of this Warrant so transferred shall be issued
to the transferee and a New Warrant evidencing the remaining portion of this
Warrant not so transferred, if any, shall be issued to the transferring Holder.
The acceptance of the New Warrant by the transferee thereof shall be deemed the
acceptance of such transferee of all of the rights and obligations of a holder
of a Warrant.

         (c) This Warrant is exchangeable, upon the surrender hereof by the
Holder to the office of the Company specified in or pursuant to Section 3(b) for
one or more New Warrants, evidencing in the aggregate the right to purchase the
number of Warrant Shares which may then be purchased hereunder.

     3. Duration and Exercise of Warrant.

         (a) This Warrant shall be exercisable by the then registered Holder on
any business day before 5:00 P.M., California time, at any time and from time to
time on or after the date hereof to and including the Expiration Date. At 5:00
P.M., California time on the Expiration Date, the portion of this Warrant not
exercised prior thereto shall be and become void and of no value.

         (b) Subject to Sections 2(c), and 5, upon surrender of this Warrant,
with the Form of Election to Purchase attached hereto duly completed and signed,
to the Company at its address for notice set forth in Section 11 and upon
payment of the Exercise Price multiplied by the number of Warrant Shares that
the Holder intends to purchase hereunder, in the manner provided hereunder, all
as specified by the Holder in the Form of Election to Purchase, the Company
shall promptly (but in no event later than 3 business days after the Date of
Exercise (as defined herein)) issue or cause to be issued and cause to be
delivered to or upon the written order of the Holder and in such name or names
as the Holder may designate, a certificate for the Warrant Shares issuable upon
such exercise, free of restrictive legends except (i) either in the event that a
registration statement covering the resale of the Warrant Shares and naming the
Holder as a selling stockholder thereunder is not then effective or the Warrant
Shares are not freely transferable without volume restrictions pursuant to Rule
144(k) promulgated under the Securities Act of 1933, as amended (the "Securities
Act"), or (ii) if this Warrant shall have been issued pursuant to a written
agreement between the original Holder and the Company, as required by such
agreement. Any person so designated by the Holder to receive Warrant Shares
shall be deemed to have become holder of record of such Warrant Shares as of the
Date of Exercise of this Warrant.

         A "Date of Exercise" means the date on which the Company shall have
received (i) this Warrant (or any New Warrant, as applicable), with the Form of
Election to Purchase attached hereto (or attached to such New Warrant)
appropriately completed and duly signed, and (ii) payment of the Exercise Price
for the number of Warrant Shares so indicated by the holder hereof to be
purchased.

                                      -2-
<PAGE>

         (c) This Warrant shall be exercisable, either in its entirety or, from
time to time, for a portion of the number of Warrant Shares. If less than all of
the Warrant Shares which may be purchased under this Warrant are exercised at
any time, the Company shall issue or cause to be issued, at its expense, a New
Warrant evidencing the right to purchase the remaining number of Warrant Shares
for which no exercise has been evidenced by this Warrant.

         (d) Prior to the exercise of this Warrant, the Holder shall not be
entitled to any rights as a stockholder of the Company with respect to the
Warrant Shares, including (without limitation) the right to vote such shares,
receive dividends or other distributions thereon or be notified of stockholder
meetings (except as otherwise set forth in Section 8(f) herein).

     4. Redemption.

         (a) The remaining unexercised portion of this Warrant may be completely
redeemed at the option of the Company at any time prior to exercise if, at the
time notice of such redemption is given by the Company as provided in Section
4(b) below, the Daily Price has exceeded $26.00 per share for any 10 consecutive
trading days immediately preceding the date of such notice, at a price equal to
$0.25 per Warrant Share then subject to the unexercised portion of this Warrant
(the "Redemption Price"). For the purpose of the foregoing sentence, the term
"Daily Price" shall mean, for any relevant day, the closing bid price or closing
price of the Common Stock, as the case may be, on that day as reported by the
principal exchange, national market or quotation system on which prices for the
Common Stock are reported. On the date set for redemption in the redemption
notice (the "Redemption Date") the Holder of record of this Warrant shall be
entitled to payment of the Redemption Price upon surrender of such redeemed
Warrant to the Company at the principal office of the Company.

         (b) Notice of redemption of Warrant shall be given at least 30 days
prior to the Redemption Date by mailing, by registered or certified mail, return
receipt requested, a copy of such notice to the Holder of this Warrant at the
address appearing on the Warrant Register or such other address designated in
writing by the holder of record to the Company not less than 40 days prior to
the Redemption Date.

         (c) From and after the Redemption Date, all rights of the Holder
(except the right to receive the Redemption Price) with respect to this Warrant
shall terminate.

         (d) The Company shall pay to the Holder of this Warrant all monies to
which the Holder of this Warrant is entitled, provided such Holder shall have
surrendered this Warrant to the Company. The Holder shall have no right to
interest following the Redemption Date unless the Company shall have defaulted
in its obligation to deliver the Redemption Price.

     5. Payment of Taxes. The Company will pay any documentary stamp taxes
attributable to the issuance of Warrant Shares upon the exercise of this
Warrant; provided, however, that the Company shall not be required to pay any
tax which may be payable in respect of any transfer involved in the registration
of any certificates for Warrant Shares or Warrants in a name other than that of
the Holder. The Holder shall be responsible for all other tax liability that may
arise as a result of holding or transferring this Warrant or receiving Warrant
Shares upon exercise hereof.

     6. Replacement of Warrant. If this Warrant is mutilated, lost, stolen or
destroyed, the Company shall issue or cause to be issued in exchange and
substitution for and upon cancellation


                                      -3-
<PAGE>

hereof, or in lieu of and substitution for this Warrant, a New Warrant, but only
upon receipt of evidence reasonably satisfactory to the Company of such loss,
theft or destruction and indemnity, if requested, satisfactory to it. Applicants
for a New Warrant under such circumstances shall also comply with such other
reasonable regulations and procedures and pay such other reasonable charges as
the Company may prescribe.

     7. Reservation of Warrant Shares. The Company covenants that it will at all
times reserve and keep available out of the aggregate of its authorized but
unissued Common Stock, solely for the purpose of enabling it to issue Warrant
Shares upon exercise of this Warrant as herein provided, the number of Warrant
Shares which are then issuable and deliverable upon the exercise of this entire
Warrant, free from preemptive rights or any other actual contingent purchase
rights of persons other than the Holder (taking into account the adjustments and
restrictions of Section 8). The Company covenants that all Warrant Shares that
shall be so issuable and deliverable shall, upon issuance and the payment of the
applicable Exercise Price in accordance with the terms hereof, be duly and
validly authorized, issued and fully paid and nonassessable.

     8. Certain Adjustments. The Exercise Price and number of Warrant Shares
issuable upon exercise of this Warrant are subject to adjustment from time to
time as set forth in this Section 8. Upon each such adjustment of the Exercise
Price pursuant to this Section 8, the Holder shall thereafter prior to the
Expiration Date be entitled to purchase, at the Exercise Price resulting from
such adjustment, the number of Warrant Shares obtained by multiplying the
Exercise Price in effect immediately prior to such adjustment by the number of
Warrant Shares issuable upon exercise of this Warrant immediately prior to such
adjustment and dividing the product thereof by the Exercise Price resulting from
such adjustment.

         (a) If the Company, at any time while this Warrant is outstanding, (i)
shall pay a stock dividend (except scheduled dividends paid on outstanding
preferred stock as of the date hereof which contain a stated dividend rate) or
otherwise make a distribution or distributions on shares of its Common Stock or
on any other class of capital stock and not the Common Stock) payable in shares
of Common Stock, (ii) subdivide outstanding shares of Common Stock into a larger
number of shares, or (iii) combine outstanding shares of Common Stock into a
smaller number of shares, the Exercise Price shall be multiplied by a fraction
of which the numerator shall be the number of shares of Common Stock (excluding
treasury shares, if any) outstanding before such event and the denominator shall
be the number of shares of Common Stock (excluding treasury shares, if any)
outstanding after such event. Any adjustment made pursuant to this Section shall
become effective immediately after the record date for the determination of
stockholders entitled to receive such dividend or distribution and shall become
effective immediately after the effective date in the case of a subdivision or
combination, and shall apply to successive subdivisions and combinations.

         (b) In case of any reclassification of the Common Stock, any
consolidation or merger of the Company with or into another person, the sale or
transfer of all or substantially all of the assets of the Company or any
compulsory share exchange pursuant to which the Common Stock is converted into
other securities, cash or property, then the Holder shall have the right
thereafter to exercise this Warrant only into the shares of stock and other
securities and property receivable upon or deemed to be held by holders of
Common Stock following such reclassification, consolidation, merger, sale,
transfer or share exchange, and the Holder shall be entitled upon such event to
receive such amount of securities or property equal to the amount of Warrant
Shares such Holder would have been entitled to had such Holder exercised this
Warrant immediately prior to such reclassification, consolidation, merger, sale,
transfer or share exchange. The terms of any such consolidation, merger,


                                      -4-
<PAGE>

sale, transfer or share exchange shall include such terms so as to continue to
give to the Holder the right to receive the securities or property set forth in
this Section 8(b) upon any exercise following any such reclassification,
consolidation, merger, sale, transfer or share exchange.

         (c) If the Company, at any time while this Warrant is outstanding,
shall distribute to all holders of Common Stock (and not to holders of this
Warrant) evidences of its indebtedness or assets or rights or warrants to
subscribe for or purchase any security (excluding those referred to in Sections
8(a), and (b)), then in each such case the Exercise Price shall be determined by
multiplying the Exercise Price in effect immediately prior to the record date
fixed for determination of stockholders entitled to receive such distribution by
a fraction of which the denominator shall be the Exercise Price determined as of
the record date mentioned above, and of which the numerator shall be such
Exercise Price on such record date less the then fair market value at such
record date of the portion of such assets or evidence of indebtedness so
distributed applicable to one outstanding share of Common Stock as determined by
the Company's independent certified public accountants that regularly examines
the financial statements of the Company (an "Appraiser").

         (d) For the purposes of this Section 8, the following clauses shall
also be applicable:

          (i)  Record Date. In case the Company shall take a record of the
               holders of its Common Stock for the purpose of entitling them (A)
               to receive a dividend or other distribution payable in Common
               Stock or in securities convertible or exchangeable into shares of
               Common Stock, or (B) to subscribe for or purchase Common Stock or
               securities convertible or exchangeable into shares of Common
               Stock, then such record date shall be deemed to be the date of
               the issue or sale of the shares of Common Stock deemed to have
               been issued or sold upon the declaration of such dividend or the
               making of such other distribution or the date of the granting of
               such right of subscription or purchase, as the case may be.

          (ii) Treasury Shares. The number of shares of Common Stock outstanding
               at any given time shall not include shares owned or held by or
               for the account of the Company, and the disposition of any such
               shares shall be considered an issue or sale of Common Stock.

         (e) All calculations under this Section 8 shall be made to the nearest
cent or the nearest 1/100th of a share, as the case may be.

         (f) If:

          (i)  the Company shall declare a dividend (or any other distribution)
               on its Common Stock; or

          (ii) the Company shall declare a special nonrecurring cash dividend on
               or a redemption of its Common Stock; or

                                      -5-
<PAGE>
          (iii) the Company shall authorize the granting to all holders of the
                Common Stock rights or warrants to subscribe for or purchase any
                shares of capital stock of any class or of any rights; or

          (iv)  the approval of any stockholders of the Company shall be
                required in connection with any reclassification of the Common
                Stock of the Company, any consolidation or merger to which the
                Company is a party, any sale or transfer of all or substantially
                all of the assets of the Company, or any compulsory share
                exchange whereby the Common Stock is converted into other
                securities, cash or property; or

          (v)   the Company shall authorize the voluntary dissolution,
                liquidation or winding up of the affairs of the Company,

then the Company shall cause to be mailed to each Holder at their last addresses
as they shall appear upon the Warrant Register, at least 30 calendar days prior
to the applicable record or effective date hereinafter specified, a notice
stating (x) the date on which a record is to be taken for the purpose of such
dividend, distribution, redemption, rights or warrants, or if a record is not to
be taken, the date as of which the holders of Common Stock of record to be
entitled to such dividend, distributions, redemption, rights or warrants are to
be determined or (y) the date on which such reclassification, consolidation,
merger, sale, transfer or share exchange is expected to become effective or
close, and the date as of which it is expected that holders of Common Stock of
record shall be entitled to exchange their shares of Common Stock for
securities, cash or other property deliverable upon such reclassification,
consolidation, merger, sale, transfer, share exchange, dissolution, liquidation
or winding up; provided, however, that the failure to mail such notice or any
defect therein or in the mailing thereof shall not affect the validity of the
corporate action required to be specified in such notice.

     9. Payment of Exercise Price. The Holder shall pay the Exercise Price in
immediately available funds by certified check or bank draft payable to the
order of the Company or by wire transfer to an account designated by the
Company.

     10. Fractional Shares. The Company shall not be required to issue or cause
to be issued fractional Warrant Shares on the exercise of this Warrant. The
number of full Warrant Shares which shall be issuable upon the exercise of this
Warrant shall be computed on the basis of the aggregate number of Warrant Shares
purchasable on exercise of this Warrant so presented. If any fraction of a
Warrant Share would, except for the provisions of this Section 10, be issuable
on the exercise of this Warrant, the Company shall pay an amount in cash equal
to the Exercise Price multiplied by such fraction.

     11. Notices. Any and all notices or other communications or deliveries
hereunder shall be in writing and shall be deemed given and effective on the
earliest of (i) the date of transmission, if such notice or communication is
delivered via facsimile at the facsimile telephone number specified in this
Section prior to 5:00 p.m. (California time) on a business day, (ii) the
business day after the date of transmission, if such notice or communication is
delivered via facsimile at the facsimile telephone number specified in this
Section later than 5:00 p.m. (California time) on any date and earlier than
11:59 p.m. (California time) on such date, (iii) the business day following the
date of mailing, if sent by nationally recognized overnight courier service, or
(iv) upon actual receipt by the party to whom such notice is required to be
given. The addresses for such communications shall be:


                                      -6-
<PAGE>

(i) if to the Company, to 157 Technology Drive, Irvine, CA 92618, Attention:
Chief Financial Officer, or to facsimile no. (949) 788-6706, or (ii) if to the
Holder, to the Holder at the address or facsimile number appearing on the
Warrant Register or such other address or facsimile number as the Holder may
provide to the Company in accordance with this Section 11.

     12. Warrant Agent. The Company shall serve as warrant agent under this
Warrant. The Company may appoint a new warrant agent upon notice to the Holder
in accordance with Section 11. Any corporation into which the Company may be
merged or any corporation resulting from any consolidation to which the Company
shall be a party or any corporation to which the Company transfers substantially
all of its corporate assets shall be a successor warrant agent under this
Warrant without any further act. Any such successor warrant agent shall promptly
cause notice of its succession as warrant agent to be mailed (by first class
mail, postage prepaid) to the Holder at the Holder's last address as shown on
the Warrant Register.

     13. Miscellaneous.

         (a) This Warrant shall be binding on and inure to the benefit of the
parties hereto and their respective successors and permitted assigns. This
Warrant may be amended only in writing signed by the Company and the Holder and
their successors and assigns.

         (b) Subject to Section 13(a), above, nothing in this Warrant shall be
construed to give to any person or corporation other than the Company and the
Holder any legal or equitable right, remedy or cause under this Warrant. This
Warrant shall inure to the sole and exclusive benefit of the Company and the
Holder.

         (c) This Warrant shall be governed by and construed and enforced in
accordance with the internal laws of the State of California without regard to
the principles of conflicts of law thereof. The Company and the Holder hereby
irrevocably submit to the exclusive jurisdiction of the state and federal courts
sitting in Orange County, California, for the adjudication of any dispute
hereunder or in connection herewith or with any transaction contemplated hereby
or discussed herein, and hereby irrevocably waives, and agrees not to assert in
any suit, action or proceeding, any claim that it is not personally subject to
the jurisdiction of any such court, or that such suit, action or proceeding is
improper. Each of the Company and the Holder hereby irrevocably waives personal
service of process and consents to process being served in any such suit, action
or proceeding by receiving a copy thereof sent to the Company at the address in
effect for notices to it under this instrument and agrees that such service
shall constitute good and sufficient service of process and notice thereof.
Nothing contained herein shall be deemed to limit in any way any right to serve
process in any manner permitted by law.

         (d) The headings herein are for convenience only, do not constitute a
part of this Warrant and shall not be deemed to limit or affect any of the
provisions hereof.

         (e) In case any one or more of the provisions of this Warrant shall be
invalid or unenforceable in any respect, the validity and enforceability of the
remaining terms and provisions of this Warrant shall not in any way be affected
or impaired thereby and the parties will attempt in good faith to agree upon a
valid and enforceable provision which shall be a commercially reasonable
substitute therefor, and upon so agreeing, shall incorporate such substitute
provision in this Warrant.

                                      -7-
<PAGE>

         IN WITNESS WHEREOF, the Company has caused this Warrant to be duly
executed by its authorized officer as of the date first indicated above.



                           NEOTHERAPEUTICS, INC.


                           By:              /s/Samuel Gulko
                                 -----------------------------------------------

                           Name:            Samuel Gulko
                                 -----------------------------------------------

                           Title: Chief Financial Officer, Secretary & Treasurer


                                      -8-
<PAGE>


                          FORM OF ELECTION TO PURCHASE

(To be executed by the Holder to exercise the right to purchase shares of Common
Stock under the foregoing Warrant)

To NeoTherapeutics, Inc.:

         In accordance with the Warrant enclosed with this Form of Election to
Purchase, the undersigned hereby irrevocably elects to purchase __________
shares of Common Stock ("Common Stock"), $.001 par value per share, of
NeoTherapeutics, Inc. encloses herewith $__________ in cash, certified or
official bank check or checks, which sum represents the aggregate Exercise Price
(as defined in the Warrant) for the number of shares of Common Stock to which
this Form of Election to Purchase relates, together with any applicable taxes
payable by the undersigned pursuant to the Warrant.

         The undersigned requests that certificates for the shares of Common
Stock issuable upon this exercise be issued in the name of

                                  PLEASE INSERT SOCIAL SECURITY OR
                                  TAX IDENTIFICATION NUMBER


                                  ----------------------------------------------

--------------------------------------------------------------------------------
                         (Please print name and address)

         If the number of shares of Common Stock issuable upon this exercise
shall not be all of the shares of Common Stock which the undersigned is entitled
to purchase in accordance with the enclosed Warrant, the undersigned requests
that a New Warrant (as defined in the Warrant) evidencing the right to purchase
the shares of Common Stock not issuable pursuant to the exercise evidenced
hereby be issued in the name of and delivered to:


--------------------------------------------------------------------------------
                         (Please print name and address)

--------------------------------------------------------------------------------


--------------------------------------------------------------------------------

Dated:  __________, ____                Name of Holder:

                                        (Print)
                                                --------------------------------

                                        (By:)
                                                --------------------------------

                                        (Name:)
                                        (Title:)
                                        (Signature must conform in all respects
                                        to name of holder as specified on the
                                        face of the Warrant)


<PAGE>


                               FORM OF ASSIGNMENT

           [To be completed and signed only upon transfer of Warrant]

         FOR VALUE RECEIVED, the undersigned hereby sells, assigns and transfers
unto ____________________ the right represented by the Warrant enclosed with
this Form of Assignment to purchase __________ shares of Common Stock of
NeoTherapeutics, Inc. to which the Warrant relates and appoints
____________________ attorney to transfer said right on the books of
NeoTherapeutics, Inc. with full power of substitution in the premises.


Dated:  __________, ____


                                        ---------------------------------------

                                        (Signature must conform in all respects
                                        to name of holder as specified on the
                                        face of the Warrant)


                                        ---------------------------------------
                                        Address of Transferee

                                        ---------------------------------------

                                        ---------------------------------------



In the presence of:


--------------------------