<PAGE>

                                                                   Exhibit 10.53
                                                                   -------------


THIS SECURITY HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933.  NO SALE
OR DISPOSITION MAY BE EFFECTED WITHOUT THE PRIOR WRITTEN CONSENT OF THE COMPANY
OR WITHOUT AN EFFECTIVE REGISTRATION STATEMENT RELATED THERETO OR AN OPINION OF
COUNSEL FOR THE HOLDER, REASONABLY SATISFACTORY TO THE COMPANY, THAT SUCH
REGISTRATION IS NOT REQUIRED UNDER THE ACT.

THIS WARRANT MAY NOT BE EXERCISED EXCEPT IN COMPLIANCE WITH ALL APPLICABLE
FEDERAL AND STATE SECURITIES LAWS TO THE REASONABLE SATISFACTION OF THE COMPANY
AND LEGAL COUNSEL FOR THE COMPANY.


                              WARRANT TO PURCHASE
                       1,570,932 SHARES OF COMMON STOCK
                                      of
                               drkoop.com, Inc.
                            a Delaware corporation

                                    Issued
                                 July 1, 1999

     THIS CERTIFIES THAT, for value received, America Online, Inc. (as the
context requires, "AOL" or the "Warrantholder") is entitled to purchase, on the
terms hereof, one million five hundred seventy thousand nine hundred thirty-two
(1,570,932) shares (subject to adjustment as set forth herein, "Warrant Stock"),
of common stock, par value $.001 per share ("Common Stock") of drkoop.com, Inc.,
a Delaware corporation (the "Company"), at a purchase price and upon the terms
and conditions as set forth herein.

1.   EXERCISE OF WARRANT.

     The terms and conditions upon which this Warrant may be exercised and the
shares of Common Stock covered hereby that may be purchased, are as follows:

     1.1.  Exercise.
           --------

           (a) This Warrant is being issued pursuant to an Interactive Services
     Agreement, dated as of the date hereof (as same may be amended, the "ISA"),
     between the Company and AOL.  All terms used but not defined herein shall
     have the meanings set forth in the ISA.  This Warrant may be exercised, in
     whole or in part, with respect to all of the Warrant Stock, at any time or
     from time to time on or after June 30, 2000.

           (b) Notwithstanding the foregoing, this Warrant may be exercised, in
     whole or in part, for all shares of Warrant Stock, subject to adjustment as
     set forth herein, as exist immediately prior to (A) recommendation of a
     Liquidity Event by the Board of Directors of the Company to its
     Stockholders, or (B) the consummation of a Liquidity Event, whichever is

     earliest to occur.  As used herein, the term "Liquidity Event" shall mean
     --------
     (i) a merger, consolidation, business combination or other transaction (a
     "Merger Transaction") in which the Company is not the surviving entity
     (provided that a Merger Transaction in which the Stockholders of the
     Company immediately prior to such Merger Transaction hold at least a
     majority of the total voting power of all classes of voting stock of the
     Company upon consummation of such Merger Transaction shall not constitute a
     "Liquidity Event"); (ii) sale,
<PAGE>

     spin-off or other transfer of all or substantially all of the Company's
     assets to an unrelated third party; (iii) a liquidation or dissolution of
     the Company; or (iv) within any period of twelve (12) consecutive months,
     any "person" or "group" (each as defined in Section 13(d) of the Securities
     Exchange Act of 1934, as amended (the "Exchange Act")) who or which was not
     an "Affiliate" (as defined in the Exchange Act) of the Company at the
     beginning of such period, becomes the "beneficial owner" (as defined in
     Rule 13 d-3 under the Exchange Act) of more than thirty percent (30%) of
     the total voting power of all classes of voting stock of the Company.

           (c) Notwithstanding the foregoing, this Warrant may not be exercised
     under any circumstances after 5:00 p.m., Austin, Texas time on June 30,
     2008 (the "Termination Date"), after which time this Warrant shall
     terminate and shall be void and of no further force of effect.

     1.2.  Exercise Price.  The purchase price for the shares of Common Stock to
           --------------
be issued upon exercise of this Warrant shall be Fifteen Dollars and Ninety-Four
Cents ($15.94) per share, subject to adjustment as set forth herein (the
"Exercise Price").

     1.3.  Method of Exercise.  The exercise of the purchase rights evidenced by
           ------------------
this Warrant shall be effected by (a) the surrender of this Warrant, together
with a duly executed copy of the form of Election to Purchase attached hereto,
to the Company at its principal office and (b) the delivery of the Exercise
Price multiplied by the number of shares for which the purchase rights hereunder
are being exercised, payable (x) by certified check, corporate check of America
Online, Inc., or wire transfer of immediately available funds payable to the
Company's order or (y) on a net basis, such that, without the exchange of any
funds, the Warrantholder receives that number of shares otherwise issuable (or
other consideration payable) upon exercise of this Warrant less that number of
shares of Warrant Stock having an aggregate fair market value (as defined below)
at the time of exercise (i.e., the date a duly executed Election to Purchase is
delivered to the Company) equal to the aggregate Exercise Price that would
otherwise have been paid by the Warrantholder for the shares of the Warrant
Stock issuable.  In connection with such exercise the holder shall, if requested
by the Company, include confirmation of the accuracy of the representations set
forth in Section 12 and otherwise as reasonably requested by the Company to
evidence compliance with any applicable securities laws as of the date of
exercise.  For purposes of the foregoing, "fair market value" of the Warrant
Stock on any date shall be the average of the Quoted Prices of the Common Stock
of the Company for 20 consecutive trading days ending the trading day prior to
such date (if, during such 30-day period, there is a day in which no trades are
reported, such date shall be discarded and the 20-day period extended).  The
"Quoted Price" of the Common Stock as reported by Nasdaq or, if the principal
trading market for the Common Stock is then a securities exchange, the last
reported sales price of the Common Stock on such exchange which shall be
consolidated trading if applicable to such exchange, or if neither so reported
or listed, the last reported bid price of the Common Stock.  In the absence of
quotation or listing, such determination as to "Quoted Price" shall be made in
good faith by the Board of Directors of the Company after taking into
consideration all factors it deems appropriate, including, without limitation,
recent sale and offer prices of the capital stock of the Company in private
transactions negotiated at arm's length.

     1.4.  Issuance of Shares.  In the event that the purchase rights evidenced
           ------------------
by this Warrant are exercised in whole or in part in accordance with the terms
of this Warrant, a certificate or certificates for the purchased shares shall be
issued to the Warrantholder as soon as practicable.  The Warrant Stock shall be
stamped or imprinted with a legend in substantially the following form:

     "THIS SECURITY HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933.
     NO SALE OR OTHER DISPOSITION MAY BE EFFECTED WITHOUT THE PRIOR WRITTEN
     CONSENT OF THE COMPANY AND WITHOUT AN

                                       2
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                                                                    Confidential

     EFFECTIVE REGISTRATION STATEMENT RELATED THERETO OR AN OPINION OF COUNSEL
     FOR THE HOLDER, SATISFACTORY TO THE COMPANY, THAT SUCH REGISTRATION IS NOT
     REQUIRED UNDER THE ACT."

     In the event the purchase rights evidenced by this Warrant are exercised in
part, the Company will also issue to the Warrantholder a new warrant within a
reasonable time representing the unexercised purchase rights.

     1.5   Exercise of Warrants on Termination Date.  If as of the Termination
           ----------------------------------------
Date the Warrants are in the money based on the cash or other property to be
received, such exercise shall take place automatically with respect to all then
outstanding and exercisable (but not exercised) Warrants (the "Termination Date
Exercise"), on a net exercise basis, immediately prior to the Termination Date;
provided, however, that the Company may condition such exercise on the delivery
by the Warrantholder of a duly completed Election to Purchase and the reasonable
satisfaction of the Company that all applicable securities laws have been
complied with, which the Company shall give notice to the Warrantholder of
within ten (10) days prior to the Termination Date.  No such Termination Date
Exercise shall take place if such issuance would not comply with applicable
securities laws, whereupon the Termination Date shall occur as scheduled.

2.   CERTAIN ADJUSTMENTS.
     -------------------

     2.1.  Stock Dividends.  If at any time while this Warrant remains
           ---------------
outstanding and unexpired, the Company pays a dividend or makes a distribution
with respect to the Common Stock payable in shares of Common Stock, then the
Exercise Price shall be adjusted, as of the record date of stockholders
established for such purpose (or if no such record is taken, as at the date of
such payment or distribution), to that price determined by multiplying the
Exercise Price in effect immediately prior to such payment or distribution by a
fraction (A) the numerator of which shall be the total number of shares of
Common Stock outstanding immediately prior to such dividend or distribution, and
(B) the denominator of which shall be the total number of shares of Common Stock
outstanding immediately after such dividend or distribution.  The Warrantholder
shall thereafter be entitled to purchase, at the Exercise Price resulting from
such adjustment, the number of shares of Common Stock (calculated to the nearest
whole share) obtained by multiplying the Exercise Price in effect immediately
prior to such adjustment by the number of shares of Common Stock issuable upon
the exercise hereof immediately prior to such adjustment and dividing the
product thereof by the Exercise Price resulting from such adjustment.  The
provisions of this Section 2.1 shall not apply under any of the circumstances
for which an adjustment is provided under Sections 2.2, 2.3 or 2.4.

     2.2.  Mergers, Consolidations or Sale of Assets.  If at any time while this
           -----------------------------------------
Warrant remains outstanding and unexpired, there shall be a capital
reorganization of the shares of the Company's capital stock (other than a
combination, reclassification, exchange or subdivision otherwise provided for
herein), or a merger or consolidation of the Company with or into another
corporation in which the Company is not the surviving corporation (collectively,
a "Corporate Transaction"), then lawful provision shall be made so that such
successor corporation or entity shall assume this Warrant such that the
Warrantholder shall thereafter be entitled to receive, upon exercise of this
Warrant, during the period specified in this Warrant and upon payment of the
Exercise Price then in effect, the number of shares of stock or other securities
or property of the successor corporation resulting from such Corporate
Transaction to which a holder of the securities deliverable upon exercise of
this Warrant would have been entitled under the provisions of the agreement in
such Corporate Transaction if this Warrant had been exercised immediately prior
to such Corporate Transaction.  Appropriate adjustment (as determined in good
faith

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                                                                    Confidential

by the Company's Board of Directors after taking into consideration all
factors it deems appropriate, including, without limitation, recent sale and
offer prices of the capital stock of the Company in private transactions
negotiated at arm's length) shall be made in the application of the provisions
of this Warrant with respect to the rights and interests of the Warrantholder
after the Corporate Transaction to the end that the provisions of this Warrant
(including adjustment of the Exercise Price then in effect and the number of
shares of Common Stock issuable under this Warrant) shall be applicable after
the Corporate Transaction, as near as reasonably may be, in relation to any
shares or other property deliverable after the Corporate Transaction upon
exercise of this Warrant.  The provisions of this Section 2.2 shall similarly
apply to successive reorganizations, consolidations or mergers.

     2.3.  Reclassification.  If the Company at any time shall, by subdivision,
           ----------------
combination or reclassification or securities or otherwise, change any of the
securities issuable under this Warrant into the same or a different number of
securities of any other class or classes, this Warrant shall thereafter
represent the right to acquire such number and kind of securities as would have
been issuable as a result of such change with respect to the securities issuable
under this Warrant immediately prior to such subdivision, combination,
reclassification or other change.

     2.4.  Subdivision or Combination of Shares.  If at any time while this
           ------------------------------------
Warrant remains outstanding and unexpired, the number of shares of Common Stock
outstanding is decreased by a combination of the outstanding shares of Common
Stock, then the Exercise Price shall be proportionately increased in the case of
a combination of such shares, or shall be proportionately decreased in the case
of a subdivision of such shares, and the number of shares of Common Stock
issuable upon exercise of the Warrant shall thereafter be adjusted to equal the
product obtained by multiplying the number of shares of Common Stock issuable
under this Warrant immediately prior to such Exercise Price adjustment by a
fraction (A) the numerator of which shall be the Exercise Price immediately
prior to such adjustment, and (B) the denominator of which shall be the Exercise
Price immediately after such adjustment.

     2.5.  Liquidating Dividends, Etc.  If the Company at any time while the
           ---------------------------
Warrant remains outstanding and unexpired makes a distribution of its assets to
the holders of its Common Stock as a dividend in liquidation or by way of return
of capital or other than as a dividend payable out of earnings or surplus
legally available for dividends under applicable law or any distribution to such
holders made in respect of the sale of all or substantially all of the Company's
assets (other than under the circumstances provided for in the foregoing
Sections 2.1 through 2.4), the holder of this Warrant shall be entitled to
receive upon the exercise hereof, in addition to the shares of Common Stock
receivable upon such exercise, and without payment of any consideration other
than the Exercise Price, an amount in cash equal to the value of such
distribution per share of Common Stock multiplied by the number of shares of
Common Stock which, on the record date for such distribution, are issuable upon
exercise of this Warrant (with no further adjustment being made following any
event which causes a subsequent adjustment in the number of shares of Common
Stock issuable upon the exercise hereof), and an appropriate provision therefor
should be made a part of any such distribution.  The value of a distribution
which is paid in other than cash shall be determined in good faith by the Board
of Directors.

     2.6.  Notice of Adjustments.  Whenever any of the Exercise Price or the
           ---------------------
number of securities purchasable under the terms of this Warrant at that
Exercise Price shall be adjusted pursuant to Section 2 hereof, the Company shall
promptly notify the Warrantholder in writing of such adjustment, setting forth
in reasonable detail the event requiring the adjustment, the amount of the
adjustment, the method by which such adjustment was calculated, and the Exercise
Price and number of shares of Common Stock or other securities issuable at that
Exercise Price after giving effect to such adjustment.  Such notice shall be
mailed (by first class and postage prepaid) to the registered Warrantholder.  In
the event of:

                                       4
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                                                                    Confidential

          (a)  The taking by the Company of a record of the holders of any class
of securities of the Company for the purpose of determining the holders thereof
who are entitled to receive any dividend or other distribution, or any right to
subscribe for, purchase or otherwise acquire any shares of stock of any class or
any other securities or property, or to receive any other right for which no
adjustment is required by the operation of this Section 2,

          (b)  Any capital reorganization of the Company, any reclassification
or recapitalization of the capital stock of the Company or any transfer of all
or substantially all of the assets of the Company to any other person or any
consolidation or merger involving the Company for which no adjustment is
required by the operation of this Section 2, or

          (c)  Any voluntary or involuntary dissolution, liquidation, or
winding-up of the Company,

the Company will mail (by first class and postage prepaid) to the Warrantholder,
at its last address at least ten (10) days prior to the earliest date specified
therein as described below, a notice specifying:

               (i)    The date on which any such record is to be taken for the
     purpose of such dividend, distribution or right, and the amount and
     character of such dividend, distribution or right; and

               (ii)   The date on which any such reorganization,
     reclassification, transfer, consolidation, merger, dissolution, liquidation
     or winding-up is expected to become effective and the record date for
     determining shareholders entitled to vote thereon.

     Failure to give any notice required under this Section 2.6, or any defect
in such notice, shall not affect the legality or validity of the underlying
corporate action taken or transaction entered into by the Company.

3.   FRACTIONAL SHARES.
     -----------------

     No fractional shares shall be issued in connection with any exercise of
this Warrant.  In lieu of the issuance of such fractional share, the Company
shall make a cash payment equal to the then fair market value of such fractional
share as determined under Section 1.3.

4.   RESERVATION OF COMMON STOCK.
     ---------------------------

     The Company shall at all times reserve and keep available out of its
authorized but unissued shares of Common Stock, solely for the purpose of
effecting the exercise of this Warrant, a sufficient number of shares of Common
Stock to effect the exercise of the entire Warrant and if at any time the number
of authorized but unissued shares of Common Stock shall not be sufficient to
effect the exercise of the entire Warrant, in addition to such other remedies as
shall be available to the holder of this Warrant, the Company will use its
reasonable efforts to take such corporate action as may, in the opinion of its
counsel, be necessary to increase its authorized but unissued shares of Common
Stock to such number of shares as shall be sufficient for such purposes.

5.   PRIVILEGE OF STOCK OWNERSHIP.
     ----------------------------

     Other than as set forth herein, prior to the exercise of this Warrant and
the issuance to the Warrantholder of certificates representing the resulting
shares of Common Stock, and except as

                                       5
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                                                                    Confidential

otherwise provided herein, the Warrantholder shall not be entitled, by virtue of
holding this Warrant, to any rights of a Stockholder of the Company, including
(without limitation) the right to vote, receive dividends or other distributions
or be notified of Stockholder meetings, and such holder shall not be entitled to
any notice or other communication concerning the business or affairs of the
Company, except as required by law.

6.   LIMITATION OF LIABILITY.
     -----------------------

     No provision hereof, in the absence of affirmative action by the holder
hereof to purchase the securities issuable under this Warrant, and no mere
enumeration herein of the rights of privileges of the holder hereof, shall give
rise to any liability of such holder for the purchase price or as a Stockholder
of the Company, whether such liability is asserted by the Company or by
creditors of the Company.

7.   TRANSFERS AND EXCHANGES.
     -----------------------

     This Warrant may be transferred or assigned in whole or in part at any time
or from time to time on or after December 8, 1999, provided such transfer
complies with all applicable federal and state securities laws and the
requirements of any legend on this Warrant.

8.   PAYMENT OF TAXES.
     ----------------

     The Company shall pay all stamp or similar issue or transfer taxes payable
in respect of the issue or delivery of the securities issuable under this
Warrant.  The Company shall not be required, however, to pay any tax or other
charge imposed in connection with any transfer involved in the issue of any
certificate for shares of the securities issuable under this Warrant in any name
other than that of the Warrantholder, and in such case, the Company shall not be
required to issue or deliver any stock certificate until such tax or other
charge has been paid or it has been established to the Company's satisfaction
that no such tax or other charge is due.

9.   NO IMPAIRMENT OF RIGHTS.
     -----------------------

     The Company hereby agrees that it will not, through the amendment of its
Certificate of Incorporation or otherwise, avoid or seek to avoid the observance
or performance of any of the terms of this Warrant, but will at all times in
good faith assist in the carrying out of all such terms and in the taking of all
such actions as may be necessary or appropriate in order to protect the rights
of the Warrantholder against impairment.

                                       6
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                                                                    Confidential

10.  SUCCESSORS AND ASSIGNS.
     ----------------------

     The terms and provisions of this Warrant shall be binding upon the Company
and the Warrantholder and their respective successors and assigns.

11.  LOSS, THEFT, DESTRUCTION OR MUTILATION OF WARRANT
     -------------------------------------------------

     Upon receipt by the Company of evidence reasonably satisfactory to it of
the loss, theft, destruction or mutilation of this Warrant, and in case of loss,
theft or destruction, upon receipt of an indemnity or security reasonably
satisfactory to the Company, and upon reimbursement to the Company of all
reasonable expenses incidental thereto, and upon surrender and cancellation of
this Warrant, if mutilated, the Company will make and deliver a new warrant of
like tenor and dated as of such cancellation, in lieu of this Warrant.

12.  SECURITIES LAW MATTERS.
     ----------------------

     Warrantholder represents to the Company as follows:

          (a)  the Warrants and Common Stock to be acquired by Warrantholder
pursuant hereto will be acquired for its own account and not with a view to, or
intention of, distribution thereof in violation of the Securities Act of 1933
(the "Securities Act") or any applicable state securities laws, and such
securities will not be disposed of in contravention of the Securities Act or any
applicable state securities laws;

          (b)  the Warrantholder understands that (a) the Warrants and Common
Stock issuable on exercise have not been registered under the Securities Act,
nor qualified under the securities laws of any other jurisdiction, (b) such
securities cannot be resold unless they subsequently are registered under the
Securities Act and qualified under applicable state securities laws, unless the
Company determines that exemptions from such registration and qualification
requirements are available, and (c) this Warrant does not grant the
Warrantholder any right to require such registration or qualification;

          (c)  Warrantholder is familiar with the term "accredited investor" as
defined in Rule 501 under the Securities Act and investor is an "accredited
investor" within the meaning of such term in Rule 501 under the Securities Act;

          (d)  Warrantholder is sophisticated in financial matters and the
market for Internet companies and is able to evaluate the risks and benefits of
the investment in the Warrants and Common Stock issuable on exercise;

          (e)  Warrantholder is able to bear the economic risk of its investment
in the Warrants and the Common Stock issuable on exercise for an indefinite
period of time; and

          (f)  Warrantholder has had an opportunity to ask questions and receive
answers concerning the terms and conditions of the offering of securities and
has had full access to such other information concerning the Company as investor
has requested.

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                                                                    Confidential

13.  SATURDAYS, SUNDAYS, HOLIDAYS.
     ----------------------------

     If the last or appointed day for the taking of any action or the expiration
of any right required or granted herein shall be a Saturday or Sunday or shall
be a legal holiday, then such action may be taken or such right may be exercised
on the next succeeding day not a legal holiday.

14.  GOVERNING LAW.
     --------------

     This Warrant shall be construed, interpreted, and the rights of the Company
and the Warrantholder determined in accordance with the internal laws of the
State of Delaware, without regard to the conflict of laws provision thereof.

15.  BENEFITS OF THIS WARRANT.
     -------------------------

     Nothing in this Warrant shall be construed to give any person other than
the Company and the registered Warrantholder any legal or equitable right,
remedy or claim.

16.  COUNTERPARTS.
     -------------

     This Warrant may be exercised in counterpart with each constitution; an
original and together constituting but one and the same Warrant.

                            (signature page follows)

                                       8
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                                                                    Confidential

     IT WITNESS WHEREOF, drkoop.com, Inc. has caused this Warrant to be duly
executed and delivered to the Warrantholder identified below on the date first
set forth above.

                                  drkoop.com, Inc.



                                  By:
                                     -----------------------------------
                                     Donald W. Hackett
                                     Chief Executive Officer

Dated:  July 1, 1999



Acknowledged and Accepted:
--------------------------

America Online, Inc.



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

Address for Notice:
22000 AOL Way
Dulles, VA  20166
Attention:  General Counsel

                                       9
<PAGE>

                                                                    Confidential

                             ELECTION TO PURCHASE
                             --------------------

drkoop.com, Inc.
________________
________________

Ladies and Gentlemen:

     The undersigned hereby elects to purchase, pursuant to the provisions of
the Warrant dated July 1, 1999 held by the undersigned, _________ shares of the
Common Stock of drkoop.com, Inc., a Delaware corporation.

     Payment of the per share purchase price required under such Warrant
[accompanies this Election to Purchase.][shall be made pursuant to the net
exercise provision contained in Section 1.3 of the Warrant.]

     The undersigned hereby confirms the representations made in Section 12 of
the Warrant are true and correct as of the date of this Election to Purchase.

Dated: ___________________, 200_


                                  -----------------------------------
                                  Print Name of Warrantholder


                                  By
                                    -----------------------------------
                   Address:
                                    -----------------------------------

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

                                       10