<PAGE>

                                                                   EXHIBIT 10.19

                        COMMON STOCK PURCHASE AGREEMENT

     This Common Stock Purchase Agreement ("Agreement") by and between
PlanetRX.com, Inc. (the "Company"), and Alpha Venture Capital, Inc., a Cook
Islands corporation (the "Purchaser"), is dated as of July 25, 2000.

                                    Recitals
                                    --------

     A.  Purchaser desires to purchase, and the Company desires to sell, shares
of the Company's Common Stock, on the terms and conditions as are set forth
below, and in connection therewith, the Company shall issue certain warrants to
the Purchaser, including an Initial Warrant for 500,000 shares of common stock.

     B.  The parties intend that the issuance of the Subscribed Shares as
anticipated by this Agreement shall be accomplished without registration under
the Securities Act of 1933, as amended (the "Securities Act"), and without
registration or qualification under the securities laws of any state or other
jurisdiction in reliance on exemptions from the registration requirements of the
Securities Act, including without limitation Regulation D under the Securities
Act and Section 4(2) of the Securities Act; provided, however, that a condition
                                            --------  -------
to Purchaser's obligation to accept Subscribed Shares hereunder is that the
resale of such Subscribed Shares be permitted pursuant to the Registration
Statement contemplated by the Registration Rights Agreement executed
concurrently herewith and that the Purchaser otherwise be able to resell such
Subscribed Shares in accordance with applicable laws.

     THEREFORE, in consideration of the mutual promises and covenants set forth
below and for other good and valuable consideration, the receipt and sufficiency
of which the parties acknowledge by their signatures below, the parties agree as
follows (capitalized terms shall have the meanings ascribed to such terms in
Exhibit A hereto, unless otherwise indicated):
---------

     1.  Initial Warrant.  Upon execution hereof, the Company shall deliver to
         ---------------
Purchaser the Initial Warrant duly executed on behalf of the Company.

     2.  Agreement to Purchase.  The Purchaser hereby unconditionally and
         ---------------------
irrevocably agrees to purchase from the Company up to U.S.$50,000,000 of Common
Stock ("Subscribed Shares") in one or more tranches subject to the terms and
conditions provided this Agreement.

     3.  Closings.
         --------
               (a)  Subject to the terms and conditions of this Agreement, the
Company agrees to issue and sell to Purchaser, and the Purchaser agrees purchase
from the Company in immediately available funds, on each Closing Date, the
Subscribed Shares specified in the Put Notice relating to each Closing at a
purchase price equal to the Put Amount divided by the Draw Down Discount
Percentage multiplied by the Market Price of the Common Stock. Subject to the
terms and conditions of this Agreement, the Company further agrees to issue to
the Purchaser on
<PAGE>

each Closing Date Additional Warrants in an amount equal to the product of the
Put Amount and 4,180,000 divided by 50,000,000. Such Additional Warrants shall
contain legends conforming to the requirements of Section 9 hereto. Each Closing
shall occur on the related Closing Date at such place, time and date as the
parties may mutually agree to in writing.

               (b)  On the eleventh (11th) Business Day after the related Put
Notice Date (i) the Company shall deliver physical certificates representing the
Subscribed Shares specified in the Put Notice and the Additional Warrants
relating the Closing to an escrow agent via the DTC System (The Depository Trust
Company system) designated by the Company and the Purchaser and (ii) the
Purchaser shall pay to such escrow agent by wire transfer in immediately
available funds the purchase price for such Closing. Upon receipt by the escrow
agent of the items in clauses (i) and (ii) above, the escrow agent shall deliver
such Subscribed Shares and the Additional Warrants to the Purchaser via the DTC
System (The Depository Trust Company system) and pay the purchase price by wire
transfer in immediately available funds to the Company.

      4.  Put Notice Procedure.  Commencing on or before the Effective Date, the
          --------------------
Company may provide a notice (a "Put Notice") to the Purchaser.  The date the
Put Notice is received by the Purchaser is referred to herein as the "Put Notice
Date"  The Put Notice shall specify the dollar amount (the "Put Amount") of the
Common Stock to be purchased by the Purchaser.  Each Put Notice shall specify a
Put Amount (i) not less than five hundred thousand dollars (U.S.$500,000), (ii)
not more than eight million dollars (U.S.$8,000,000) and (iii) not more than an
amount equal to four hundred percent (400%) of the Trading Volume for the twenty
(20) consecutive Business Days immediately preceding the related Put Notice
Date.

      5.  Representations and Warranties of Purchaser.  To induce the Company's
          -------------------------------------------
acceptance of this Agreement, Purchaser hereby represents and warrants to the
Company as follows:

            5.1  Intent.  Purchaser is acquiring the Securities for its own
                 ------
account and has no present arrangement (whether or not legally binding) to sell
any of the Securities to or through any Person; provided, however, that
                                                --------  -------
Purchaser does not agree to hold any of the Securities for any minimum or other
specific term and reserves the right to dispose of the Securities at any time in
accordance with U.S. federal and state securities laws applicable to such
disposition and any restrictions imposed on such transfer by this Agreement or
the instruments and documents executed in connection with this Agreement.
Purchaser has been advised or is aware of the provisions of Rule 144 promulgated
under the Securities Act.

            5.2  Sophisticated Investor.  Purchaser is an "accredited investor"
                 ----------------------
(as defined in Rule 501(a) of Regulation D) and a sophisticated investor that
has such knowledge and experience in financial and business matters as to be
capable of evaluating the merits and risks of an investment in the Securities.
Purchaser was not formed exclusively for the purpose of entering into the
transactions contemplated hereby.

            5.3  Ability of Purchaser to Bear Risk of Investment.  Purchaser
                 -----------------------------------------------
acknowledges that the Securities are speculative investments and involve a high
degree of risk. Purchaser is able to bear the economic risk of an investment in
the Securities, and is able to afford a complete loss of such investment.

                                      -2-
<PAGE>

            5.4  Authority.  This Agreement has been duly authorized and validly
                 ---------
executed and delivered by Purchaser and (assuming due authorization and valid
execution by the Company) is a legal, valid and binding agreement of Purchaser
enforceable against Purchaser in accordance with its terms, subject to general
principles of equity and to bankruptcy, insolvency or similar laws relating to,
or affecting generally the enforcement of creditors' rights and remedies or by
other equitable principles of general application. Each Person executing this
Agreement and any other Transaction Documents on behalf of Purchaser has all
requisite authority to do so on behalf of Purchaser.

            5.5  Brokers, Finders.  Purchaser has taken no action which would
                 ----------------
give rise to any claim by any Person for brokerage commission, finder's fees or
similar payments by the Company relating to this Agreement or the transactions
contemplated hereby.

            5.6  Organization; Authority.  Purchaser is an entity organized,
                 -----------------------
validly existing and in good standing under the laws of the Cook Islands with
the requisite power and authority to enter into and to consummate the
transactions contemplated by this Agreement and to carry out its obligations
thereunder. The acquisition of the Securities and the payment of the purchase
price therefor by Purchaser have been duly authorized by all necessary action on
the part of Purchaser.

            5.7  Absence of Conflicts.  The execution and delivery of this
                 --------------------
Agreement and any other document or instrument executed in connection herewith
(collectively with this Agreement, the "Transaction Documents"), and the
consummation of the transactions contemplated by the Transaction Documents, and
compliance with the requirements thereof, will not violate any law, rule,
regulation, order, writ, judgment, injunction, decree or award binding on
Purchaser, or the provision of any indenture, instrument or agreement to which
Purchaser is a party or is subject, or by which Purchaser or any of its assets
is bound, or conflict with or constitute a material default thereunder, or
require the approval of any third-party pursuant to any material contract,
agreement, instrument, relationship or legal obligation to which Purchaser is
subject or to which any of its assets, operations or management may be subject.

            5.8  Disclosure; Access to Information.  Purchaser has received
                 ---------------------------------
copies of or has had access to all documents, records, books and other
information pertaining to Purchaser's investment in the Company and the
Securities that have been requested by Purchaser. Purchaser has been afforded
the opportunity to ask questions of and receive answers from the Company and its
management concerning all aspects of the Company and of this transaction.
Purchaser further acknowledges that it understands that the Company is subject
to the periodic reporting requirements of the Securities Exchange Act of 1934,
as amended (the "Exchange Act"), and Purchaser has reviewed or received copies
of any such reports that have been requested by it. Purchaser further
acknowledges that it has been provided with copies of the Company's certificate
of incorporation, as amended (the "Certificate"), and the Company's bylaws (the
"Bylaws").

            5.9  Manner of Sale.  At no time was Purchaser presented with or
                 ---------------
solicited by or through any leaflet, public promotional meeting, television
advertisement or any other form of general solicitation or advertising with
respect to the Securities.

                                      -3-
<PAGE>

            5.10  Accuracy of Other Materials.  To the extent Purchaser has
                  ---------------------------
received from the Company documents or other materials which constitute
summaries, projections, forecasts or estimates, Purchaser acknowledges the
following with respect to such documents or other materials: Such documents or
other materials are intended to illustrate projected financial and other results
based upon a set of assumptions (in some cases based on information obtained by
the Company from outside sources) the Company views as reasonable and
obtainable; all such summaries, projections, forecasts or estimates pertaining
to revenue growth, profitability and other similar financial or market data are
forward-looking statements; such statements are subject to certain risks and
uncertainties that could cause actual results to differ materially from those
projected; and no representations or warranties of future performance by or
market trends for the Company are intended, and such are expressly disclaimed.

            5.11  Accuracy of Representations and Information.  All
                  -------------------------------------------
representations made by Purchaser in this Agreement and all documents and
instruments related to this Agreement, and all information provided by Purchaser
to the Company concerning Purchaser are correct and complete in all material
respects as of the date hereof.

      6.  Representations and Warranties of the Company. The Company hereby
          ---------------------------------------------
represents and warrants to Purchaser as follows:

            6.1  Company Status.  The Company has registered the Common Stock
                 --------------
pursuant to Section 12(g) of the Exchange Act, is in full compliance with all
reporting requirements of the Exchange Act, and the Company has maintained all
requirements for the continued listing of the Common Stock, and such Common
Stock, as of the date hereof, is listed on the NASDAQ National Market System
under the symbol "PLRX".

            6.2  Current Public Information.  The Company has furnished or made
                 --------------------------
available to Purchaser true and correct copies of all registration statements,
reports and documents, including proxy statements (other than preliminary proxy
statements), filed with the SEC by or with respect to the Company since December
31, 1999 and prior to the date of this Agreement, pursuant to the Securities Act
or the Exchange Act (collectively, the "SEC Documents").

            6.3  No General Solicitation.  Neither the Company, nor any of its
                 -----------------------
Affiliates, nor any Person acting on its or their behalf, has engaged in any
form of general solicitation or general advertising (within the meaning of
Regulation D under the Securities Act) in connection with the offer or sale of
the Securities.

            6.4  Valid Issuance of Common Stock.  The Company has an authorized
                 ------------------------------
capitalization consisting of one hundred million (100,000,000) shares of Common
Stock, and five million (5,000,000) shares preferred stock.  As of July 21, 2000
the Company had (i) 51,453,667 shares of Common Stock issued and outstanding,
(ii) no shares of preferred stock issued and outstanding, (iii) 166,740 shares
of Common Stock subject to issuance upon the conversion or exercise of presently
issued and outstanding warrants of the Company, (iv) 7,145,894 shares of Common
Stock subject to issuance upon the conversion or exercise of presently issued
and outstanding options of the Company and (v) 14,618,341 shares of Common Stock
which are reserved for issuance under the Company's existing stock option plans.
All of the shares of Common Stock outstanding have been duly and validly
authorized and issued and

                                      -4-
<PAGE>

are fully paid and non-assessable. As of the date of this Agreement, except as
may be set forth above, (i) there are no outstanding options, warrants, scrip,
rights to subscribe to, calls or commitments of any character whatsoever
relating to, or securities or rights convertible into, any shares of capital
stock of the Company or any of the Subsidiaries, or contracts, commitments,
understandings or arrangements by which the Company or any of it Subsidiaries is
or may become bound to redeem or issue additional shares of capital stock of the
Company or any of the Subsidiaries or options, warrants, scrip, rights to
subscribe to, calls or commitments of any character whatsoever relating to, or
securities or rights convertible into, any shares of capital stock of the
Company or any of the Subsidiaries, (ii) there are no outstanding debt
securities, other than indebtedness to banks and other institutional lenders set
forth on Schedule 6.4 and (iii) except for arrangements disclosed in filings by
         ------------
the Company with the SEC, there are no arrangements under which the Company or
any of the Subsidiaries is obligated to register the sale of any of their
securities under the Securities Act. Except as may be set forth in
Schedule 6.4, there are no securities or instruments containing any anti-
------------
dilution, right of first refusal, preemptive rights or similar provisions that
will be triggered by the issuance of the Securities as described in this
Agreement.  Upon issuance of the Securities, such securities will be duly and
validly issued, fully paid and non-assessable.

            6.5  Organization and Qualification.  Since December 31, 1999, no
                 ------------------------------
Material Adverse Effect has occurred with respect to the Company or its
Subsidiaries, except (i) as may be disclosed in the SEC Documents or any other
documents filed with the SEC by the Company, (ii) as may have been disclosed to
the Purchaser in writing by the Company or (iii) as may have been otherwise
publicly disclosed by the Company. The Company is a corporation duly
incorporated and existing in good standing under the laws of the Delaware and
has the requisite corporate power to own its properties and to carry on its
business as now being conducted. The Company does not have any Subsidiaries,
except for those listed on Schedule 4.5 attached to this Agreement (the
                           ------------
"Subsidiaries"). The Subsidiaries are duly incorporated and existing in good
standing under the laws of the jurisdiction of their incorporation. The Company
and each of the Subsidiaries is duly qualified as a foreign corporation to do
business and is in good standing in every jurisdiction in which the nature of
the business conducted or property owned by it makes such qualification
necessary, other than those in which the failure so to qualify would not have a
Material Adverse Effect. "Material Adverse Effect" means any effect on the
business, operations, properties or financial condition of the Company and which
is material and adverse to the Company, and/or any condition or situation which
would prohibit or otherwise interfere with the ability of the Company to enter
into and perform its obligations under the Transaction Documents.

            6.6  Authorization: Enforcement.  (i) The Company has the requisite
                 --------------------------
corporate power and authority to enter into and perform under the Transaction
Documents and to issue the Securities in accordance with the terms of the
Transaction Documents, (ii) the execution, issuance and delivery of the
Transaction Documents by the Company and the consummation by it of the
transactions contemplated by the Transaction Documents have been duly authorized
by all necessary corporate action, and no further consent or authorization of
the Company or its board of directors or stockholders is required, (iii) the
Transaction Documents have been duly executed and delivered by the Company, and
(iv) the Transaction Documents (assuming due authorization and valid and legal
execution by Purchaser) constitute legal, valid and binding obligations of the
Company enforceable against the Company in accordance with their terms,

                                      -5-
<PAGE>

except as such enforceability may be limited by applicable bankruptcy,
insolvency, or similar laws relating to, or affecting generally the enforcement
of, creditors' rights and remedies or by other equitable principles of general
application.

            6.7  Corporate Documents.  The Company has furnished or made
                 -------------------
available to Purchaser true and correct copies of the Certificate and the
Bylaws.

            6.8  No Conflicts.  The execution, delivery and performance of the
                 ------------
Transaction Documents by the Company and the consummation by the Company of the
transactions contemplated hereby, including without limitation the issuance of
the Securities, do not and will not (i) result in a violation of the Company's
Certificate or Bylaws, or (ii) conflict with, or result in a breach of or
forfeiture of any rights (or result in an event which with notice or lapse of
time or both would become a breach of or forfeiture of any rights) under, or
give to others any rights of termination, amendment, acceleration or
cancellation of, any material agreement, indenture or instrument to which the
Company or any of the Subsidiaries is a party, or (iii) result in a violation of
any federal or state law, rule, regulation, order, judgment or decree (including
federal and state securities laws and regulations) applicable to the Company or
any of the Subsidiaries or by which any property or asset of the Company or any
of the Subsidiaries is bound or affected (except for such conflicts, defaults,
terminations, amendments, accelerations, cancellations and violations as would
not, individually or in the aggregate, have a Material Adverse Effect). The
business of the Company is not being conducted in violation of any law,
ordinance or regulation of any governmental entity, except for possible
violations which either singly or in the aggregate do not and will not have a
Material Adverse Effect. The Company is not required under federal, state or
local law, rule or regulation to obtain any consent, authorization or order of,
or make any filing or registration with, any court or governmental agency in
order for it to execute, deliver or perform any of its obligations under this
Agreement or issue and sell the Securities in accordance with the terms of this
Agreement (other than any SEC, NASD or state securities filings which may be
required to be made by the Company subsequent to any closing hereunder, and any
registration statement which may be filed in furtherance of this Agreement);
provided that the Company is assuming and relying upon the accuracy of the
--------
relevant representations and agreements of Purchaser herein. Neither the Company
nor any of the Subsidiaries is in violation of any material term of or in
material default under its Certificate or Bylaws or their organizational charter
or bylaws, respectively, or any material contract, agreement, mortgage,
indebtedness, indenture, instrument, judgment, decree of order or any statute,
rule or regulation applicable to the Company or the Subsidiaries, which has not
been duly waived as of the date of this Agreement.

            6.9  SEC Documents.  As of their respective dates, the SEC Documents
                 -------------
complied, and all similar documents filed with the SEC prior to each Closing
Date will comply, in all material respects with the requirements of the
Securities Act or the Exchange Act, as the case may be, and rules and
regulations of the SEC promulgated thereunder and other federal, state and local
laws, rules and regulations applicable to such SEC Documents, and none of the
SEC Documents contained, nor will any similar document filed with the SEC prior
to each Closing Date contain, any untrue statement of a material fact or omitted
or omit to state a material fact required to be stated therein or necessary in
order to make the statements therein, in the light of the circumstances under
which they were made, not misleading. The financial statements of the Company
included in the SEC Documents, as of the dates thereof, complied, and all
similar

                                      -6-
<PAGE>

documents filed with the SEC prior to each Closing Date will comply, as to form
in all material respects with applicable accounting requirements and the
published rules and regulations of the SEC and other applicable rules and
regulations with respect thereto. Such financial statements were prepared in
accordance with generally accepted accounting principles applied on a consistent
basis during the periods involved (except (i) as may be otherwise indicated in
such financial statements or the notes thereto or (ii) in the case of unaudited
interim statements, to the extent they may not include footnotes or may be
condensed or summary statements as permitted by Form 10-QSB of the SEC) and
fairly present in all material respects the financial position of the Company
and its consolidated Subsidiaries as of the dates thereof and the consolidated
results of operations and cash flows for the periods then ended (subject, in the
case of unaudited statements, to normal year-end audit adjustments). The Company
has filed all reports and other documents required to be filed by it with the
SEC under the Exchange Act.

            6.10  No Undisclosed Liabilities.  The Company and the Subsidiaries
                  --------------------------
have no liabilities or obligations of a financial nature (whether accrued,
absolute, contingent or otherwise), which are material, individually or in the
aggregate, and are not disclosed in the SEC Documents, other than those incurred
in the ordinary course of the Company's or the Subsidiaries' respective
businesses consistent with past practice since March 31, 2000, and which,
individually or in the aggregate, do not or would not have a Material Adverse
Effect on the Company.

            6.11  Litigation and Other Proceedings.  Except as may be set forth
                  --------------------------------
in the SEC Documents or any other documents filed with the SEC by the Company or
otherwise disclosed in writing to Purchaser, there are no lawsuits or
proceedings pending or to the best knowledge of the Company threatened, against
the Company, nor has the Company received any written or oral notice of any such
action, suit, proceeding or investigation, which might have a Material Adverse
Effect on the Company or which might materially adversely affect the
transactions contemplated by this Agreement. Except as set forth in the SEC
Documents or any other documents filed with the SEC by the Company, no judgment,
order, writ, injunction or decree or award has been issued by or, to the best
knowledge of the Company, requested of any court, arbitrator or governmental
agency which might result in a Material Adverse Effect or which might materially
adversely affect the transactions contemplated by this Agreement.

            6.12  Other Documents or Materials.  With respect to any document or
                  ----------------------------
other materials received by Purchaser from the Company or its representatives
other than the Transaction Documents and the SEC Documents or any other
documents filed with the SEC by the Company, (i) the Company has no reason to
believe any of such documents and materials or any projections contained
therein, as of the date of such other documents or materials, contained material
errors or misstatements or do not adequately describe the status of the
development of the Company's technologies or its business as of such date, and
(ii) such documents, materials and projections were prepared by the Company and
its management in good faith.

            6.13  Nature of Company.  The Company is not an open ended
                  -----------------
investment company or a unit investment trust, registered or required to be
registered, or a closed end investment company required to be registered, but
not registered, under the Investment Company Act of 1940.

                                      -7-
<PAGE>

            6.14  Brokers, Finders.  Except for payment of commitment fees to
                  ----------------
Purchaser, payment of which is the sole responsibility of the Company, the
Company has taken no action which would give rise to any claim by any Person for
brokerage commission, finder's fees or similar payments by Purchaser relating to
this Agreement or the transactions contemplated hereby.

            6.15  Absence of Certain Changes.  The Company has not taken any
                  --------------------------
steps, and does not currently expect to take any steps, to seek protection
pursuant to any bankruptcy law nor does the Company or any of the Subsidiaries
have any knowledge or reason to believe that its creditors intend to initiate
involuntary bankruptcy proceedings.

            6.16  Intellectual Property Rights.  The Company and the
                  ----------------------------
Subsidiaries own or possess adequate rights or licenses to use all trademarks,
trade names, service marks, service mark registrations, service names, patents,
patent rights, copyrights, inventions, licenses, approvals, governmental
authorizations, trade secrets and rights necessary to conduct their respective
businesses as now conducted. None of the Company's trademarks, trade names,
service marks, service mark registrations, service names, patents, patent
rights, copyrights, inventions, licenses, approvals, government authorizations,
trade secrets or other intellectual property rights have expired or terminated,
or are expected to expire or terminate in the near future. The Company and the
Subsidiaries do not have any knowledge of any infringement by the Company or the
Subsidiaries of trademarks, trade name rights, patents, patent rights,
copyrights, inventions, licenses, service names, service marks, service mark
registrations, trade secrets or other similar rights of others, or of any such
development of similar or identical trade secrets or technical information by
others and, there is no claim, action or proceeding being made or brought
against, or to the best knowledge of the Company, being threatened against, the
Company or the Subsidiaries regarding trademark, trade name, patent, patent
rights, invention, copyright, license, service name, service mark, service mark
registration, trade secret or other infringement; and the Company and the
Subsidiaries are unaware of any facts or circumstances which might give rise to
any of the foregoing. The Company and the Subsidiaries have taken reasonable
security measures to protect the secrecy, confidentiality and value of all of
their intellectual properties.

            6.17  Internal Accounting Controls.  The Company is aware of no
                  ----------------------------
respect in which its system of internal accounting controls is not sufficient to
provide reasonable assurance that (i) transactions are executed in accordance
with management's general or specific authorizations, (ii) transactions are
recorded as necessary to permit preparation of financial statements in
conformity with generally accepted accounting principles and to maintain asset
accountability, (iii) access to assets is permitted only in accordance with
management's general or specific authorization and (iv) the recorded
accountability for assets is compared with the existing assets at reasonable
intervals and appropriate action is taken with respect to any differences.

            6.18  Tax Status.  The Company and the Subsidiaries have made or
                  ----------
filed all federal and state income and all other tax returns, reports and
declarations required by any jurisdiction to which it is subject and has paid
all taxes and other governmental assessments and charges that are material in
amount, shown or determined to be due on such returns, reports, declarations,
except those being contested in good faith and has set aside on its books
provisions

                                      -8-
<PAGE>

reasonably adequate for the payment of all taxes for periods subsequent to the
periods to which such returns, reports, or declarations apply. There are no
unpaid taxes in any material amount claimed to be due by the taxing authority of
any jurisdiction, and the officers of the Company know of no basis for any such
claim.

            6.19  Certain Transactions.  Except as set forth in the SEC
                  --------------------
Documents or any other documents filed with the SEC by the Company and except
for arm's length transactions pursuant to which the Company makes payments in
the ordinary course of business upon terms no less favorable than the Company
could obtain from third parties and other than the grant of stock options, none
of the officers, directors, or employees of the Company (or any spouse or
relative of any such Person) is presently a party to any transaction with the
Company (other than for services as employees, officers, consultants and
directors), including any contract, agreement or other arrangement providing for
the furnishing of services to or by, providing for rental of real or personal
property to or from, or otherwise requiring payments to or from any officer,
director or such employee or, to the knowledge of the Company, any corporation,
partnership, trust or other entity in which any officer, director, or any such
employee has a substantial interest or is an officer, director, trustee or
partner.

            6.20  Dilution.  The Chief Executive Officer and the Chief Financial
                  --------
Officer and the board of the Company have studied and the board has approved the
transactions contemplated by this Agreement, which may have a potential dilutive
effect. The Company has concluded, in its good faith business judgment, that
such issuance is in the best interests of the Company.

            6.21  NASDAQ Listing.  The Company's Common Stock is presently
                  --------------
quoted on the NASDAQ National Market System under the symbol "PLRX." The Company
is not in receipt of any written notice from any stock exchange, market or
trading facility on which the Common Stock is or has been listed (or on which it
is or has been quoted) to the effect that the Company is not in compliance with
the listing or maintenance requirements of such stock exchange, market or
trading facility or that the Common Stock will be delisted from such stock
exchange, market or trading facility.

            6.22  No Integrated Offering.  Neither the Company nor any of its
                  ----------------------
Affiliates nor any Person acting on its or their behalf has, directly or
indirectly made any offer or sales of any security or solicited any offers to
buy any security under circumstances that would eliminate the availability of
the exemption from registration under Regulation D in connection with the offer
and sale of the Securities as contemplated hereby.

      7.  Company Reliance on Purchaser's Representations.  Purchaser
          -----------------------------------------------
understands that the Company is relying on the truth and accuracy of the
representations and warranties made herein by Purchaser in offering the
Securities for sale and in relying upon applicable exemptions available under
the Securities Act and applicable state securities laws.

      8.  Other Covenants of the Company.
          ------------------------------

            8.1  Furnishing of Information.  As long as Purchaser owns
                 -------------------------
Securities, the Company covenants to timely file (or obtain extensions in
respect thereof and file within the

                                      -9-
<PAGE>

applicable grace period) all reports required to be filed by the Company after
the date hereof pursuant to Section 13(a) or 15(d) of the Exchange Act. If at
any time prior to the date on which Purchaser may resell all of the Securities
without volume restrictions pursuant to Rule 144(k) promulgated under the
Securities Act (as determined by counsel to the Company pursuant to a written
opinion letter to such effect, addressed and acceptable to the Company's
transfer agent for the benefit of and enforceable by Purchaser) the Company is
not required to file reports pursuant to such sections, it will prepare and
furnish to Purchaser and make publicly available in accordance with Rule 144(c)
promulgated under the Securities Act annual and quarterly financial statements,
together with a discussion and analysis of such financial statements in form and
substance substantially similar to those that would otherwise be required to be
included in reports required by Section 13(a) or 15(d) of the Exchange Act in
the time period that such filings would have been required to have been made
under the Exchange Act. The Company further covenants that it will take such
further action as any holder of Securities may reasonably request, all to the
extent required from time to time to enable such Person to sell Securities
without registration under the Securities Act within the limitation of the
exemptions provided by Rule 144 promulgated under the Securities Act.

            8.2  Certain Agreements.  During the period commencing on the date
                 ------------------
hereof and ending on the earlier of (i) the termination of this Agreement
pursuant to Section 11.13 and (ii) the date on which the Purchaser has purchased
from the Company U.S.$50,000,000 of Common Stock, the Company shall provide the
Purchaser with written notice ("Company Notice") of the Company's intent to
raise capital through the issuance of additional equity securities in a private
transaction not registered with the SEC at least five (5) Business Days prior to
the closing date for such transaction. If within five (5) Business Days of the
date on which the Purchaser receives notice of such transaction, the Purchaser
provides the Company with written notice that the Purchaser is exercising a
right of first refusal to purchase such additional equity securities at terms
better than or equal to those specified in the Company Notice, the Company shall
enter into such transaction with the Purchaser. If the Purchaser declines to
exercise its right of first refusal, or fails to do so within the time period
described above, the Company may proceed with the proposed offering on the terms
described in the Company Notice. The Provisions of this Section 8.2 shall not
apply to the Company (i) raising capital by issuing its equity securities (or
instruments convertible into or exercisable for equity securities) to strategic
partners and/or in connection with mergers or acquisitions, (ii) issuing
securities (other than for cash) in connection with a merger, consolidation,
sale of assets, disposition or the exchange of the capital stock for assets,
stock or other joint venture interests or (iii) converting or exercising any
convertible or derivative securities outstanding on the date hereof. The Company
and the Purchaser further acknowledge that the provisions of this Section 8.2
shall not be binding upon any successors or assigns of the parties hereto.

            8.3  Available Shares.  At all times until the termination of this
                 ----------------
Agreement, prior to each Closing the Company shall have authorized and reserved
for issuance the shares required to be issued at such Closing.

                                      -10-
<PAGE>

      9.  Legends.  So long as the Registration Statement relating to resales of
          -------
the Securities of the Company has been declared effective by SEC, the Company
shall issue certificates representing Securities with the following legend:

          THE SHARES REPRESENTED BY THIS CERTIFICATE MAY NOT BE SOLD,
          TRANSFERRED, PLEDGED, HYPOTHECATED OR OTHERWISE DISPOSED OF
          IN ANY MANNER UNLESS THE HOLDER OR A BROKER, ON BEHALF OF
          THE HOLDER, REPRESENTS THAT IT HAS COMPLIED WITH THE PROSPECTUS
          DELIVERY REQUIREMENTS CONTAINED IN SECTION 5 OF THE SECURITIES
          ACT OF 1933, AS AMENDED, OR UNLESS AN EXEMPTION FROM THE
          REGISTRATION PROVISIONS OF SUCH ACT IS AVAILABLE.

If the Registration Statement relating to resales of the Securities of the
Company is not effective at the time of issuance, the Company shall issue
certificates representing the Securities with the following legend:


          THESE SECURITIES HAVE NOT BEEN REGISTERED WITH THE SECURITIES
          AND EXCHANGE COMMISSION OR THE SECURITIES COMMISSION OF ANY
          STATE IN RELIANCE UPON AN EXEMPTION FROM REGISTRATION UNDER
          THE 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, OR IN A
          TRANSACTION NOT SUBJECT TO, THE REGISTRATION REQUIREMENTS OF
          THE SECURITIES ACT AND IN ACCORDANCE WITH APPLICABLE STATE
          SECURITIES LAWS.

      10.  Conditions to Closings.
           ----------------------

            10.1  Conditions to the Company's Obligation to Sell.  The Purchaser
                  ----------------------------------------------
understands that the Company's obligation to sell the Subscribed Shares on each
Closing Date pursuant to this Agreement is conditioned upon the following:

                  (a)  the accuracy on each such date of the representations and
warranties of Purchaser contained in this Agreement as if made thereon, and the
performance by Purchaser on or before such date of all covenants and agreements
of Purchaser required to be performed on or before such date;

                                      -11-
<PAGE>

                  (b)  there not being in effect any law, rule or regulation
prohibiting or restricting the transactions contemplated hereby, or requiring
any consent or approval which shall not have been obtained, nor there being any
pending or threatened proceeding or investigation which may have the effect of
prohibiting or adversely affecting any of the transactions contemplated by this
Agreement.

            10.2  Conditions to Purchaser's Obligation To Purchase.  The Company
                  ------------------------------------------------
understands that Purchaser's obligation to purchase the Subscribed Shares on
each Closing Date pursuant to this Agreement is conditioned upon the following:

                  (a)  the accuracy in all material respects on each such date
of the representations and warranties of the Company contained in this Agreement
as if made on such date and the performance by the Company on or before each
such date of all covenants and agreements of the Company required to be
performed on or before such date;

                  (b)  there not being in effect any law, rule or regulation
prohibiting or restricting the transactions contemplated hereby, or requiring
any consent or approval which shall not have been obtained, nor there being any
pending or threatened proceeding or investigation which may have the effect of
prohibiting or adversely affecting any of the transactions contemplated by this
Agreement;

                  (c)  a registration statement relating to the Registration
Rights Agreement shall be effective, and if previously suspended shall be
effective and have been effective for at least fifteen (15) days prior to the
Closing Date, and shall relate to the Subscribed Shares and the Additional
Warrants to be issued in such Closing;

                  (d)  the trading of the Common Stock shall not be suspended by
the SEC or the NASD;

                  (e)  the Company shall be in compliance with all Blue Sky laws
necessary to issue and resell through a broker in the State of California the
Subscribed Shares relating to such Closing;

                  (f)  as of the date hereof, (i) the Company shall not have
materially changed its line of business (ii) the Company shall not be material
in default under any of its existing debt or loan obligations, (iii) there shall
be no current SEC finding of wrongdoing by the Company, (iv) there shall be no
final adverse determination against the Company by a court or governmental
agency and (v) no bankruptcy proceeding shall be initiated with respect to the
Company, in each case which has a Material Adverse Effect; and

                  (g)  the Company shall deliver to the Purchaser an opinion of
counsel substantially in the form of Exhibit D hereto.

     11.  Miscellaneous.
          -------------

          11.1  Assignment.  Neither this Agreement nor any rights of the
                ----------
parties hereunder may be assigned by either party to any other Person without
the prior written consent of the other party hereto; provided, however, that the
                                                     --------  -------
Company may assign its rights hereunder

                                      -12-
<PAGE>

in connection with a merger, consolidation, sale of assets, disposition or the
exchange of capital stock of the Company.

          11.2  Attorneys' Fees.  In the event any dispute arises under this
                ---------------
Agreement or the documents or instruments executed and delivered in connection
with this Agreement, and the parties hereto resort to litigation to resolve such
dispute, the prevailing party in any such litigation, in addition to all other
remedies at law or in equity, shall be entitled to an award of costs and fees
from the other party, which costs and fees shall include, without limitation,
reasonable attorneys' fees and legal costs.

          11.3  Choice of Law; Venue.  This Agreement shall be governed by and
                --------------------
interpreted in accordance with the laws of the State of California for contracts
to be wholly performed in such state and without giving effect to the principles
thereof regarding the conflict of laws. Each of the parties consents to the
jurisdiction of the federal courts whose districts encompass any part of the
City of San Francisco or the state courts of the State of California sitting in
the City of San Francisco in connection with any dispute arising under this
Agreement and hereby waives, to the maximum extent permitted by law, any
objection, including any objection based on forum non coveniens, to the bringing
of any such proceeding in such jurisdictions.

          11.4  Costs and Expenses.  The parties shall be responsible for and
                ------------------
shall pay their own costs and expenses, including without limitation attorneys'
fees and accountants' fees and expenses, in connection with the conduct of the
due diligence inquiry, negotiation, execution and delivery of this Agreement and
the instruments, documents and agreements executed in connection with this
Agreement, except that the Company shall within five (5) Business Days of the
date of the execution of this Agreement pay to Krieger & Prager, Esqs., legal
counsel for the Purchaser, by wire transfer in immediately available funds,
U.S.$45,000.00 representing legal and general expenses of the Purchaser.

          11.5  Counterparts/Facsimile Signatures.  This Agreement may be
                ---------------------------------
executed in one or more counterparts, each of which when so signed shall be
deemed to be an original, and such counterparts together shall constitute one
and the same instrument. In lieu of the original, a facsimile transmission or
copy of the original shall be as effective and enforceable as the original.

          11.6  Entire Agreement: Amendment.  This Agreement, together with the
                ---------------------------
exhibits and schedules to this Agreement and the other instruments and documents
delivered in connection with this Agreement constitute the full and entire
understanding and agreement between the parties with regard to the subjects
hereof and thereof, and no party shall be liable or bound to any other party in
any manner by any warranties, representations or covenants except as
specifically set forth in this Agreement or therein. Except as expressly
provided in this Agreement, neither this Agreement nor any term hereof may be
amended, waived, discharged or terminated other than by a written instrument
signed by the party against whom enforcement of any such amendment, waiver,
discharge or termination is sought.

                                      -13-
<PAGE>

          11.7  Headings.  The headings of the sections and paragraphs of this
                --------
Agreement have been inserted for convenience of reference only and do not
constitute a part of this Agreement.

          11.8  Notices.  All notices or other communications provided for under
                -------
this Agreement shall be in writing, and mailed, telecopied or delivered by hand
delivery or by overnight courier service, as follows:

               If to the Company:

               PlanetRX.com, Inc.
               349 Oyster Point Boulevard, Suite 201
               South San Francisco, CA 94080
               Attn.:  CFO.
               Fax No.:  (650) 616-1585

               With a copy to:

               PlanetRX.com, Inc.
               349 Oyster Point Boulevard, Suite 201
               South San Francisco, CA 94080
               Attn.: General Counsel
               Fax No.: (650) 616-1585

               If to Purchaser:

               Alpha Venture Capital, Inc.
               [_______________]
               [_______________]
               [_______________]
               Attention:  Mr. Barry Herman, Director
               Fax No.:  [________________]

               With a copy to:

               Krieger & Prager, Esqs.
               39 Broadway, Suite 1440
               New York, NY 10006
               Attention:  Samuel M. Krieger, Esq.
               Fax No.:  (212) 213-2077


All notices and communications shall be effective as follows:  When mailed, upon
three (3) Business Days after deposit in the mail (postage prepaid); when
telecopied, upon confirmed transmission of the telecopied notice; when hand
delivered, upon delivery; and when sent by overnight courier, the next Business
Day after deposit of the notice with the overnight courier.

                                      -14-
<PAGE>

          11.9  Publicity.  Purchaser acknowledges that this Agreement and all
                ---------
or part of the Transaction Documents may be deemed to be "material contracts" as
that term is defined by Item 601(b)(10) of Regulation S-B, and that the Company
may therefore be required to file such documents as exhibits to reports or
registration statements filed under the Securities Act or the Exchange Act.
Purchaser further agrees that the status of such documents and materials as
material contracts shall be determined solely by the Company, in consultation
with its counsel. Purchaser consents to the Company's public disclosure of this
Agreement in accordance with the Securities Act and the Exchange Act.

          11.10  Severability.  Should any one or more of the provisions of this
                 ------------
Agreement be determined to be illegal or unenforceable, all other provisions of
this Agreement shall be given effect separately from the provision or provisions
determined to be illegal or unenforceable and shall not be affected thereby.

          11.11  Survival of Representations and Warranties.  The Company's
                 ------------------------------------------
representations and warranties herein shall survive the execution and delivery
of this Agreement and the delivery of the Securities, and shall inure to the
benefit of Purchaser and its successors and permitted assigns. The Purchaser's
representations and warranties herein shall survive the execution and delivery
of this Agreement and the delivery of the Securities, and shall inure to the
benefit of Company and its successors and permitted assigns.

          11.12  Schedules and Exhibits.  The schedules and exhibits attached to
                 ----------------------
this Agreement are a part hereof, as if fully set forth herein.

          11.13  Termination.  The obligations of the parties hereunder shall
                 -----------
expire one (1) year from the Effective Date; provided that in the event that
                                             --------
during the initial twelve (12) months after the Effective Date, Purchaser
purchases at least ten million dollars (U.S.$10,000,000) in Common Stock
pursuant to this Agreement, the terms of this Agreement shall be automatically
extended for an additional period of twelve (12) months, unless the Company in
its sole discretion elects not to extend the term of this Agreement and provides
notice of such election to Purchaser; and provided, further, that the
                                          --------  -------
obligations of the parties hereunder shall expire on December 7, 2000 if one or
more Registration Statements relating to the Warrants and the Subscribed Shares
has not been declared effective by the SEC.

          11.14  Successors and Assigns.  This Agreement will inure to the
                 ----------------------
benefit of and be binding upon the parties hereto and, unless otherwise provided
herein, their respective successors and assigns.

                                      -15-
<PAGE>

     IN WITNESS WHEREOF, the parties named below have caused this Agreement to
be executed and delivered as of the date first above written.

                                    PLANETRX.COM, INC

                                    By:
                                       ------------------------------
                                       Name:
                                       Title:

                                    ALPHA VENTURE CAPITAL, INC.

                                    By:
                                       ------------------------------
                                       Name:
                                       Title:

                                      -16-
<PAGE>

                                   Exhibit A
                                   ---------

                                  DEFINITIONS
                                  -----------

"Additional Warrant" means a warrant in the form of Exhibit B hereto to purchase
                                                    ---------
a number of shares of Common Stock equal to ten percent (10%) of the number of
Additional Shares.

"Affiliate" has the meaning set forth in the Exchange Act and the rules and
regulations thereunder.

"Business Day" means a day on which the Nasdaq stock market is open for regular
trading.

"Closing" means each of the transactions described in Section 3.

"Closing Date" means the tenth (10th) Business Day after the related Put Notice
Date.

"Common Stock" means common stock, $0.0001 par value per share, of the Company.

"Draw Down Discount Percentage" means 91%; provided, however, that for each
                                           --------  -------
$0.50 the Market Price increases from $1.50 as of the related Put Date, the Draw
Down Discount Percentage shall increase by 0.25%, incrementally, to a maximum of
97%.

"Effective Date" means the date the registration statement filed pursuant to the
Registration Rights Agreement is declared effective by the SEC.

"Exchange Act" is defined in Section 5.8.

"Initial Warrant" means a warrant in the form of Exhibit C hereto.
                                                 ---------

"Market Price" of the Common Stock shall equal the average of the five (5)
lowest reported VWAP of the Common Stock for the ten (10) trading days
immediately after the related Put Date.

"Material Adverse Effect" is defined in Section 6.5.

"NASD" means the National Association of Securities Dealers.

"Person" means an individual, corporation, partnership, association, trust,
estate or other entity or organization, including a governmental entity or
agency.

"Put Notice" is defined in Section 4.

"Registration Rights Agreement" means the registration rights agreement in the
form of Exhibit D hereto.
        ---------

"SEC" means the Securities and Exchange Commission.

"SEC Documents" is defined in Section 6.2.

                                      A-1
<PAGE>

"Securities" means the Subscribed Shares, the Warrants and the shares issuable
under the Warrants.

"Securities Act" is as defined in Recital B.

"Share Valuation Date" means the fifth (5th) Business Day after the related Put
Notice Date.

"Subscribed Shares" is defined in Section 2.

"Subsidiaries" is defined in Section 6.5.

"Trading Volume" means the dollar amount of the average daily trading volume of
the Common Stock, calculated based on the average close bid price and average
daily trading volume over the twenty (20) Business Days preceding the related
Put Date, in each case as reported by Bloomberg, LP.

"Transaction Documents" is defined in Section 5.7.

"VWAP" means the daily volume weighted average price (based on a trading day
from 9:30 a.m. to 4:00 p.m., eastern time) of the Company's Common Stock on the
NASDAQ National Market System (or any successor thereto) as reported by
Bloomberg Financial LP using the AQR function.

"Warrants" means the Initial Warrant and the Additional Warrants.

                                      A-2
<PAGE>

                                   Exhibit B
                                   ---------

                            FORM OF INITIAL WARRANT
                            -----------------------

THESE SECURITIES AND THE SECURITIES ISSUABLE UPON THEIR EXERCISE HAVE NOT BEEN
REGISTERED UNDER THE SECURITIES ACT OF 1933 (THE "1933 ACT") AND MAY NOT BE
TRANSFERRED UNLESS COVERED BY AN EFFECTIVE REGISTRATION STATEMENT UNDER THE ACT,
OR TRANSFERRED IN A TRANSACTION MEETING THE REQUIREMENTS OF RULE 144 OF THE ACT
OR OTHERWISE IN ACCORDANCE WITH AN EXEMPTION FROM THE REGISTRATION REQUIREMENTS
OF THE ACT.

                               PlanetRX.com, Inc.

                         COMMON STOCK PURCHASE WARRANT

     1.  Issuance.  In consideration of good and valuable consideration, the
         --------
receipt of which is hereby acknowledged by PLANETRX.COM, INC., a Delaware
corporation (the "Company"), ALPHA VENTURE CAPITAL, INC., (the "Holder") is
hereby granted the right to purchase at any time commencing July [__], 2000
until 5:00 P.M., New York City time, on July [__], 2003 (the "Expiration Date"),
Five Hundred Thousand (500,000) fully paid and nonassessable shares of the
Company's Common Stock, par value $.0001 per share (the "Common Stock") at an
initial exercise price of the lesser of 150% of the average closing bid price of
the Common Stock for the three (3) consecutive trading days prior to the date of
the execution of Common Stock Purchase Agreement, dated as of July [__], 2000
(the "Common Stock Purchase Agreement"), between the Holder and the Company or
120% of the average closing bid price of the Common Stock for the three (3)
consecutive trading days prior to Effective Date of the Registration Statement
or (the "Exercise Price"), subject to further adjustment as set forth in Section
6 hereof.

     2.  Exercise of Warrants.  (a)  This Warrant is exercisable in whole or in
         --------------------
part at the Exercise Price per share of Common Stock payable hereunder, payable
in cash or by certified or official bank check, or by "cashless exercise," by
means of tendering this Warrant to the Company to receive a number of shares of
Common Stock equal to the difference between the Market Value of the shares of
Common Stock issuable upon exercise of this Warrant and the product of the
number of shares issuable upon exercise and the Exercise Price, divided by the
Market Value Per Share.  For example, if Holder receives a warrant to purchase
1,500,000 shares of Common Stock at an Exercise Price of $1.00 and decides to
use the "cashless exercise" method to exercise its option to purchase all
1,500,000 shares at a time when the Company's Common Stock has a Market Value
Per Share of $10.00, Holder would receive 1,350,000 shares of Common Stock upon
exercise.  Upon surrender of this Warrant with the annexed Notice of Exercise
Form duly executed, together with payment of the Exercise Price for the shares
of Common Stock purchased, the Holder shall be entitled to receive a certificate
or certificates for the shares of Common Stock so purchased.  For the purposes
of this Section 2, "Market Value" shall be an amount equal to the Market Value
Per Share multiplied by the number of shares of Common Stock to be issued upon
surrender of this Warrant, and "Market Value Per Share" shall

                                      B-1
<PAGE>

be an amount equal to the average closing sales price of a share of Common Stock
for the ten (10) consecutive trading days preceding the Company's receipt of the
duly executed Notice of Exercise Form.

          (b) For purposes of Rule 144 promulgated under the Securities Act, it
is intended, understood and acknowledged that the Warrant Shares issued in a
cashless exercise transaction shall be deemed to have been acquired by the
Holder and the holding period for the Warrant Shares shall be deemed to have
been commenced, on the issue date.

     3.  Reservation of Shares.  The Company hereby agrees that at all times
         ---------------------
during the term of this Warrant there shall be reserved for issuance upon
exercise of this Warrant such number of shares of its Common Stock as shall be
required for issuance upon exercise of this Warrant (the "Warrant Shares").

     4.  Mutilation or Loss of Warrant.  Upon receipt by the Company of evidence
         -----------------------------
satisfactory to it of the loss, theft, destruction or mutilation of this
Warrant, and (in the case of loss, theft or destruction) receipt of an indemnity
bond or other satisfactory indemnification, and (in the case of mutilation) upon
surrender and cancellation of this Warrant, the Company will execute and deliver
a new Warrant of like tenor and date and any such lost, stolen, destroyed or
mutilated Warrant shall thereupon become void.

     5.  Rights of the Holder.  The Holder shall not, by virtue hereof, be
         --------------------
entitled to any rights of a stockholder in the Company, either at law or equity,
and the rights of the Holder are limited to those expressed in this Warrant and
are not enforceable against the Company except to the extent set forth herein.

     6.  Protection Against Dilution.
         ---------------------------

          (a) Adjustment Mechanism.  If an adjustment of the Exercise Price is
              --------------------
required pursuant to this Section 6, the Holder shall be entitled to purchase
such number of additional shares of Common Stock as will cause (i) the total
number of shares of Common Stock Holder is entitled to purchase pursuant to this
Warrant, multiplied by (ii) the adjusted purchase price per share (the "Adjusted
Exercise Price"), to equal (iii) the total number of shares of Common Stock
Holder is entitled to purchase before adjustment multiplied by the Exercise
Price before adjustment.  For example, if Holder receives a warrant to purchase
1,500,000 shares of Common Stock at an Exercise Price of $1.00 per share, and
the Adjusted Exercise Price is $0.50, Holder will be entitled to receive
3,000,000 shares of Common Stock in exchange for payment of $1.5 million.

          (b) Capital Adjustments.  In case of any stock split or reverse stock
              -------------------
split, stock dividend, reclassification of the Common Stock, recapitalization,
merger or consolidation, or like capital adjustment affecting the Common Stock
of the Company, the provisions of this Section 6 shall be applied as if such
capital adjustment event had occurred immediately prior to the date of this
Warrant and the original purchase price had been fairly allocated to the stock
resulting from such capital adjustment; and in other respects the provisions of
this Section shall be applied in a fair, equitable and reasonable manner so as
to give effect, as nearly as may be, to the purposes hereof.

                                      B-2
<PAGE>

          (c) Adjustment for Spin Off.  If, for any reason, prior to the
              -----------------------
exercise of this Warrant in full, the Company spins off or otherwise divests
itself of a part of its business or operations or disposes all or of a part of
its assets in a transaction (the "Spin Off") in which the Company does not
receive compensation for such business, operations or assets, but causes
securities of another entity (the "Spin Off Securities") to be issued to
security holders of the Company, then the Company shall cause (i) to be reserved
Spin Off Securities equal to the number thereof which would have been issued if
Holder had exercised its right to purchase all of the remaining Common Stock
available to Holder under this Warrant as of the close of business on the
trading day immediately before  the record date (the "Outstanding Warrants") for
determining the amount of the number of Spin Off Securities  to be issued to
security holders of the Company (the "Reserved Spin Off Shares"), and (ii) to be
issued to the Holder upon exercise of all or any of the Outstanding Warrants,
such amount of the Reserved Spin Off Shares equal to (x) the Reserved Spin Off
Shares multiplied by (y) a fraction, of which (I) the numerator is the amount of
the Outstanding Warrants then being exercised, and (II) the denominator is the
Outstanding Warrants.

          (d) Adjustment for Commitment for Subscribed Shares.  If the average
              ------------------------------------------------
closing sales price for the three consecutive Business Days prior to
effectiveness of the initial Registration Statement for the Subscribed Shares is
less than the exercise price set forth in Section 1 above, then the exercise
price of this Warrant shall be such lesser amount.  If the Registration
Statement covering the Subscribed Shares required to be filed by the Company
pursuant to Section 2(a) hereof is not declared effective by December 7, 2000,
then the commitment contained in the Common Stock Purchase Agreement (the
"Commitment") shall terminate and the Subscriber shall retain this Warrant (with
an exercise price equal to the lesser of the amount set forth in Section 1 above
or 90% of the average close bid price of the Common Stock for the three (3)
consecutive Business Days preceding December 7, 2000.

     7.  Transfer to Comply with the Securities Act; Registration Rights.  This
         ---------------------------------------------------------------
Warrant has not been registered under the Securities Act of 1933, as amended,
(the "Act") and has been issued to the Holder for investment and not with a view
to the distribution of either the Warrant or the Warrant Shares.  Neither this
Warrant nor any of the Warrant Shares or any other security issued or issuable
upon exercise of this Warrant may be sold, transferred, pledged or hypothecated
in the absence of an effective registration statement under the Act relating to
such security or an opinion of counsel satisfactory to the Company that
registration is not required under the Act.  Each certificate for the Warrant,
the Warrant Shares and any other security issued or issuable upon exercise of
this Warrant shall contain a legend on the face thereof, in form and substance
satisfactory to counsel for the Company, setting forth the restrictions on
transfer contained in this Section.

     8.  Legends.  So long as the Registration Statement relating to resales of
         -------
any physical certificate or certificates representing the Warrant Shares has
been declared effective by SEC, the Company shall issue such certificate or
certificates with the following legend:

                                      B-3
<PAGE>


          THE SHARES REPRESENTED BY THIS CERTIFICATE MAY NOT BE SOLD,
          TRANSFERRED, PLEDGED, HYPOTHECATED OR OTHERWISE DISPOSED OF
          IN ANY MANNER UNLESS THE HOLDER OR A BROKER, ON BEHALF OF
          THE HOLDER, REPRESENTS THAT IT HAS COMPLIED WITH THE PROSPECTUS
          DELIVERY REQUIREMENTS CONTAINED IN SECTION 5 OF THE SECURITIES
          ACT OF 1933, AS AMENDED, OR UNLESS AN EXEMPTION FROM THE
          REGISTRATION PROVISIONS OF SUCH ACT IS AVAILABLE.

If the Registration Statement relating to resales of any physical certificate or
certificates representing the Warrant Shares is not effective at the time of
issuance, the Company shall issue shall issue such certificate or certificates
with the following legend:

          THESE SECURITIES HAVE NOT BEEN REGISTERED WITH THE SECURITIES AND
          EXCHANGE COMMISSION OR THE SECURITIES COMMISSION OF ANY STATE IN
          RELIANCE UPON AN EXEMPTION FROM REGISTRATION UNDER THE 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, OR IN A TRANSACTION NOT SUBJECT TO, THE REGISTRATION
          REQUIREMENTS OF THE SECURITIES ACT AND IN ACCORDANCE WITH APPLICABLE
          STATE SECURITIES LAWS.

The Company agrees to file one or more registration statements for the Warrant
Shares pursuant to the Registration Rights Agreement, dated as of July [___],
2000, between the Company and the Holder.

     9.  Notices.  Any notice or other communication required or permitted
         -------
hereunder shall be in writing and shall be delivered personally, telegraphed,
telexed, sent by facsimile transmission or sent by certified, registered or
express mail, postage pre-paid.  Any such notice shall be deemed given when so
delivered personally, telegraphed, telexed or sent by facsimile transmission,
or, if mailed, two days after the date of deposit in the United States mails, as
follows:

               If to the Company:

               PlanetRX.com, Inc.
               349 Oyster Point Boulevard, Suite 201
               South San Francisco, CA 94080
               Attn.:  Steve Valenzuela, Sr. VP-Fin.
               Fax No.:  (650) 616-1585

                                      B-4
<PAGE>

               With a copy to:

               PlanetRX.com, Inc.
               349 Oyster Point Boulevard, Suite 201
               South San Francisco, CA 94080
               Attn.: Dorothy An, Esq.
               Fax No.: [_______________]

               If to Purchaser:

               Alpha Venture Capital, Inc.
               [_______________]
               [_______________]
               [_______________]
               Attention:  Mr. Barry Herman, Director
               Fax No.:  [________________]

               With a copy to:

               Krieger & Prager, Esqs.
               39 Broadway, Suite 1440
               New York, NY 10006
               Attention:  Samuel M. Krieger, Esq.
               Fax No.:  (212) 213-2077

Any party may designate another address or person for receipt of notices
hereunder by notice given  to the other parties in accordance with this Section.

     If the Company fails to deliver to the Holder certificate or certificates
representing the Warrant Shares by the third (3rd) trading day after the Date of
Exercise, the company shall pay to such Holder, in cash, as liquidated damages
and not as a penalty, $1,000 for each day after such third (3rd) Trading Day
until such certificates are delivered.  Nothing herein shall limit the Holder's
right to pursue actual damages for the Company's failure to deliver certificates
representing shares of Common Stock upon exercise within the period specified
herein and the Holder shall have the right to pursue all remedies available to
it at law or in equity including, without limitation, a decree of specific
performance and/or injunctive relief.   The exercise of any such rights shall
not prohibit the Holder from seeking to enforce damages pursuant to any other
Section hereof or under applicable law.

     10.  Supplements and Amendments; Whole Agreement.  This Warrant may be
          -------------------------------------------
amended or supplemented only by an instrument in writing signed by the parties
hereto.  This Warrant contains the full understanding of the parties hereto with
respect to the subject matter hereof and there are no representations,
warranties, agreements or understandings other than expressly contained herein.

     11.  Governing Law.  This Warrant shall be deemed to be a contract made
          -------------
under the laws of the State of California and for all purposes shall be governed
by and construed in

                                      B-5
<PAGE>

accordance with the laws of such State applicable to contracts to be made and
performed entirely within such State.

     12.  Counterparts.  This Warrant may be executed in any number of
          ------------
counterparts and each of such counterparts shall for all purposes be deemed to
be an original, and all such counterparts shall together constitute but one and
the same instrument.

     13.  Descriptive Headings.  Descriptive headings of the several Sections of
          --------------------
this Warrant are inserted for convenience only and shall not control or affect
the meaning or construction of any of the provisions hereof.

     14.  Termination of Warrant.  This Warrant shall terminate upon the earlier
          ----------------------
to occur of (A) the date which is three (3) years from the date hereof, and (B)
a breach of Subscriber's obligation to accept and pay for Subscribed Shares
under the Common Stock Purchase Agreement.

                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]

                                      B-6
<PAGE>

     IN WITNESS WHEREOF, the parties hereto have executed this Warrant as of the
day of  [________] day of July, 2000.

                                    PlanetRX.com, Inc.

                                    By:
                                       ------------------------------

                                    Alpha Venture Capital, Inc.

                                    By:
                                       ------------------------------

                                      B-7
<PAGE>

                         NOTICE OF EXERCISE OF WARRANT

     The undersigned hereby irrevocably elects to exercise the right,
represented by the Warrant Certificate dated as of ______________, to purchase
__________ shares of the Common Stock, par value $_______ per share, of
___________________ and tenders herewith payment in accordance with Section 1 of
said Common Stock Purchase Warrant.

     Please deliver the stock certificate to:

Dated:
      -----------------------
By:
   --------------------------


___ CASH:  $____________

                                      B-8
<PAGE>

                                   Exhibit C
                                   ---------

                           FORM OF SUBSEQUENT WARRANT
                           --------------------------

THESE SECURITIES AND THE SECURITIES ISSUABLE UPON THEIR EXERCISE HAVE NOT BEEN
REGISTERED UNDER THE SECURITIES ACT OF 1933 (THE "1933 ACT") AND MAY NOT BE
TRANSFERRED UNLESS COVERED BY AN EFFECTIVE REGISTRATION STATEMENT UNDER THE ACT,
OR TRANSFERRED IN A TRANSACTION MEETING THE REQUIREMENTS OF RULE 144 OF THE ACT
OR OTHERWISE IN ACCORDANCE WITH AN EXEMPTION FROM THE REGISTRATION REQUIREMENTS
OF THE ACT.

                               PlanetRX.com, Inc.

                         COMMON STOCK PURCHASE WARRANT

     1.  Issuance.  In consideration of good and valuable consideration, the
         --------
receipt of which is hereby acknowledged by PANETRX.COM, INC., a Delaware
corporation (the "Company"), ALPHA VENTURE CAPITAL, INC., (the "Holder") is
hereby granted the right to purchase at any time commencing July [__], 2000
until 5:00 P.M., New York City time, on July [__], 2003 (the "Expiration Date"),
_______________ (_______) fully paid and nonassessable shares of the Company's
Common Stock, par value $.0001 per share (the "Common Stock") at an initial
exercise price of 120% of the closing sales price on the date of the related
Closing. (the "Exercise Price"), subject to further adjustment as set forth in
Section 6 hereof.

     2.  Exercise of Warrants.  (a)  This Warrant is exercisable in whole or in
         --------------------
part at the Exercise Price per share of Common Stock payable hereunder, payable
in cash or by certified or official bank check, or by "cashless exercise," by
means of tendering this Warrant to the Company to receive a number of shares of
Common Stock equal to the difference between the Market Value of the shares of
Common Stock issuable upon exercise of this Warrant and the product of the
number of shares issuable upon exercise and the Exercise Price, divided by the
Market Value Per Share.  For example, if Holder receives a warrant to purchase
1,500,000 shares of Common Stock at an Exercise Price of $1.00 and decides to
use the "cashless exercise" method to exercise its option to purchase all
1,500,000 shares at a time when the Company's Common Stock has a Market Value
Per Share of $10.00, Holder would receive 1,350,000 shares of Common Stock upon
exercise.  Upon surrender of this Warrant with the annexed Notice of Exercise
Form duly executed, together with payment of the Exercise Price for the shares
of Common Stock purchased, the Holder shall be entitled to receive a certificate
or certificates for the shares of Common Stock so purchased.  For the purposes
of this Section 2, "Market Value" shall be an amount equal to the Market Value
Per Share multiplied by the number of shares of Common Stock to be issued upon
surrender of this Warrant, and "Market Value Per Share" shall be an amount equal
to the average closing sales price of a share of Common Stock for the ten (10)
consecutive trading days preceding the Company's receipt of the duly executed
Notice of Exercise Form.

                                      C-1
<PAGE>

          (b) For purposes of Rule 144 promulgated under the Securities Act, it
is intended, understood and acknowledged that the Warrant Shares issued in a
cashless exercise transaction shall be deemed to have been acquired by the
Holder and the holding period for the Warrant Shares shall be deemed to have
been commenced, on the issue date.

     3.  Reservation of Shares.  The Company hereby agrees that at all times
         ---------------------
during the term of this Warrant there shall be reserved for issuance upon
exercise of this Warrant such number of shares of its Common Stock as shall be
required for issuance upon exercise of this Warrant (the "Warrant Shares").

     4.  Mutilation or Loss of Warrant.  Upon receipt by the Company of evidence
         -----------------------------
satisfactory to it of the loss, theft, destruction or mutilation of this
Warrant, and (in the case of loss, theft or destruction) receipt of an indemnity
bond or other satisfactory indemnification, and (in the case of mutilation) upon
surrender and cancellation of this Warrant, the Company will execute and deliver
a new Warrant of like tenor and date and any such lost, stolen, destroyed or
mutilated Warrant shall thereupon become void.

     5.  Rights of the Holder.  The Holder shall not, by virtue hereof, be
         --------------------
entitled to any rights of a stockholder in the Company, either at law or equity,
and the rights of the Holder are limited to those expressed in this Warrant and
are not enforceable against the Company except to the extent set forth herein.

     6.  Protection Against Dilution.
         ---------------------------

          (a) Adjustment Mechanism.  If an adjustment of the Exercise Price is
              --------------------
required pursuant to this Section 6, the Holder shall be entitled to purchase
such number of additional shares of Common Stock as will cause (i) the total
number of shares of Common Stock Holder is entitled to purchase pursuant to this
Warrant, multiplied by (ii) the adjusted purchase price per share (the "Adjusted
Exercise Price"), to equal (iii) the total number of shares of Common Stock
Holder is entitled to purchase before adjustment multiplied by the Exercise
Price before adjustment.  For example, if Holder receives a warrant to purchase
1,500,000 shares of Common Stock at an Exercise Price of $1.00 per share, and
the Adjusted Exercise Price is $0.50, Holder will be entitled to receive
3,000,000 shares of Common Stock in exchange for payment of $1.5 million.

          (b) Capital Adjustments.  In case of any stock split or reverse stock
              -------------------
split, stock dividend, reclassification of the Common Stock, recapitalization,
merger or consolidation, or like capital adjustment affecting the Common Stock
of the Company, the provisions of this Section 6 shall be applied as if such
capital adjustment event had occurred immediately prior to the date of this
Warrant and the original purchase price had been fairly allocated to the stock
resulting from such capital adjustment; and in other respects the provisions of
this Section shall be applied in a fair, equitable and reasonable manner so as
to give effect, as nearly as may be, to the purposes hereof.

          (c) Adjustment for Spin Off.  If, for any reason, prior to the
              -----------------------
exercise of this Warrant in full, the Company spins off or otherwise divests
itself of a part of its business or operations or disposes all or of a part of
its assets in a transaction (the "Spin Off") in which the

                                      C-2
<PAGE>

Company does not receive compensation for such business, operations or assets,
but causes securities of another entity (the "Spin Off Securities") to be issued
to security holders of the Company, then the Company shall cause (i) to be
reserved Spin Off Securities equal to the number thereof which would have been
issued if Holder had exercised its right to purchase all of the remaining Common
Stock available to Holder under this Warrant as of the close of business on the
trading day immediately before the record date (the "Outstanding Warrants") for
determining the amount of the number of Spin Off Securities to be issued to
security holders of the Company (the "Reserved Spin Off Shares"), and (ii) to be
issued to the Holder upon exercise of all or any of the Outstanding Warrants,
such amount of the Reserved Spin Off Shares equal to (x) the Reserved Spin Off
Shares multiplied by (y) a fraction, of which (I) the numerator is the amount of
the Outstanding Warrants then being exercised, and (II) the denominator is the
Outstanding Warrants.

     7.  Transfer to Comply with the Securities Act; Registration Rights.  This
         ---------------------------------------------------------------
Warrant has not been registered under the Securities Act of 1933, as amended,
(the "Act") and has been issued to the Holder for investment and not with a view
to the distribution of either the Warrant or the Warrant Shares.  Neither this
Warrant nor any of the Warrant Shares or any other security issued or issuable
upon exercise of this Warrant may be sold, transferred, pledged or hypothecated
in the absence of an effective registration statement under the Act relating to
such security or an opinion of counsel satisfactory to the Company that
registration is not required under the Act.  Each certificate for the Warrant,
the Warrant Shares and any other security issued or issuable upon exercise of
this Warrant shall contain a legend on the face thereof, in form and substance
satisfactory to counsel for the Company, setting forth the restrictions on
transfer contained in this Section.

     8.  Legends.  So long as the Registration Statement relating to resales of
         -------
any physical certificate or certificates representing the Warrant Shares has
been declared effective by SEC, the Company shall issue such certificate or
certificates with the following legend:


          THE SHARES REPRESENTED BY THIS CERTIFICATE MAY NOT BE SOLD,
          TRANSFERRED, PLEDGED, HYPOTHECATED OR OTHERWISE DISPOSED OF IN ANY
          MANNER UNLESS THE HOLDER OR A BROKER, ON BEHALF OF THE HOLDER,
          REPRESENTS THAT IT HAS COMPLIED WITH THE PROSPECTUS DELIVERY
          REQUIREMENTS CONTAINED IN SECTION 5 OF THE SECURITIES ACT OF 1933, AS
          AMENDED, OR UNLESS AN EXEMPTION FROM THE REGISTRATION PROVISIONS OF
          SUCH ACT IS AVAILABLE.


If the Registration Statement relating to resales of any physical certificate or
certificates representing the Warrant Shares is not effective at the time of
issuance, the Company shall issue shall issue such certificate or certificates
with the following legend:

                                      C-3
<PAGE>

          THESE SECURITIES HAVE NOT BEEN REGISTERED WITH THE SECURITIES AND
          EXCHANGE COMMISSION OR THE SECURITIES COMMISSION OF ANY STATE IN
          RELIANCE UPON AN EXEMPTION FROM REGISTRATION UNDER THE 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, OR IN A TRANSACTION NOT SUBJECT TO, THE REGISTRATION
          REQUIREMENTS OF THE SECURITIES ACT AND IN ACCORDANCE WITH APPLICABLE
          STATE SECURITIES LAWS.

The Company agrees to file one or more registration statements for the Warrant
Shares pursuant to the Registration Rights Agreement, dated as of July [___],
2000, between the Company and the Holder.

     9.  Notices.  Any notice or other communication required or permitted
         -------
hereunder shall be in writing and shall be delivered personally, telegraphed,
telexed, sent by facsimile transmission or sent by certified, registered or
express mail, postage pre-paid.  Any such notice shall be deemed given when so
delivered personally, telegraphed, telexed or sent by facsimile transmission,
or, if mailed, two days after the date of deposit in the United States mails, as
follows:

               If to the Company:

               PlanetRX.com, Inc.
               349 Oyster Point Boulevard, Suite 201
               South San Francisco, CA 94080
               Attn.:  Steve Valenzuela, Sr. VP-Fin.
               Fax No.:  (650) 616-1585

                                      C-4
<PAGE>

               With a copy to:

               PlanetRX.com, Inc.
               349 Oyster Point Boulevard, Suite 201
               South San Francisco, CA 94080
               Attn.: Dorothy An, Esq.
               Fax No.: [_______________]

               If to Purchaser:

               Alpha Venture Capital, Inc.
               [_______________]
               [_______________]
               [_______________]
               Attention:  Mr. Barry Herman, Director
               Fax No.:  [________________]

               With a copy to:

               Krieger & Prager, Esqs.
               39 Broadway, Suite 1440
               New York, NY 10006
               Attention:  Samuel M. Krieger, Esq.
               Fax No.:  (212) 213-2077

Any party may designate another address or person for receipt of notices
hereunder by notice given  to the other parties in accordance with this Section.

     If the Company fails to deliver to the Holder certificate or certificates
representing the Warrant Shares by the third (3rd) trading day after the Date of
Exercise, the company shall pay to such Holder, in cash, as liquidated damages
and not as a penalty, $1,000 for each day after such third (3rd) Trading Day
until such certificates are delivered.  Nothing herein shall limit the Holder's
right to pursue actual damages for the Company's failure to deliver certificates
representing shares of Common Stock upon exercise within the period specified
herein and the Holder shall have the right to pursue all remedies available to
it at law or in equity including, without limitation, a decree of specific
performance and/or injunctive relief.   The exercise of any such rights shall
not prohibit the Holder from seeking to enforce damages pursuant to any other
Section hereof or under applicable law.

     10.  Supplements and Amendments; Whole Agreement.  This Warrant may be
          -------------------------------------------
amended or supplemented only by an instrument in writing signed by the parties
hereto.  This Warrant contains the full understanding of the parties hereto with
respect to the subject matter hereof and there are no representations,
warranties, agreements or understandings other than expressly contained herein.

     11.  Governing Law.  This Warrant shall be deemed to be a contract made
          -------------
under the laws of the State of California and for all purposes shall be governed
by and construed in accordance with the laws of such State applicable to
contracts to be made and performed entirely within such State.

                                      C-5
<PAGE>

     12.  Counterparts.  This Warrant may be executed in any number of
          ------------
counterparts and each of such counterparts shall for all purposes be deemed to
be an original, and all such counterparts shall together constitute but one and
the same instrument.

     13.  Descriptive Headings.  Descriptive headings of the several Sections of
          --------------------
this Warrant are inserted for convenience only and shall not control or affect
the meaning or construction of any of the provisions hereof.

     14.  Termination of Warrant.  This Warrant shall terminate upon the earlier
          ----------------------
to occur of (A) the date which is three (3) years from the date hereof, and (B)
a breach of Subscriber's obligation to accept and pay for Subscribed Shares
under the Common Stock Purchase Agreement.

                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]

                                      C-6
<PAGE>

     IN WITNESS WHEREOF, the parties hereto have executed this Warrant as of the
day of  [________] day of July, 2000.

                                    PlanetRX.com, Inc.

                                    By:
                                       ------------------------


                                    Alpha Venture Capital, Inc.

                                    By:
                                       -------------------------

                                      C-7
<PAGE>

                         NOTICE OF EXERCISE OF WARRANT

     The undersigned hereby irrevocably elects to exercise the right,
represented by the Warrant Certificate dated as of ______________, to purchase
__________shares of the Common Stock, par value $_______ per share, of
___________________ and tenders herewith payment in accordance with Section 1 of
said Common Stock Purchase Warrant.

     Please deliver the stock certificate to:

Dated:
      ------------------------
By:
   ---------------------------

___ CASH:  $_____________


                                      C-8