<PAGE>

                                                                 EXHIBIT 4.30


         LEINER HEALTH PRODUCTS INC.          VITA HEALTH PRODUCTS INC.
           901 EAST 233RD STREET                 150 BEGHIN AVENUE
          CARSON, CALIFORNIA 90745               WINNIPEG, MANITOBA


                                                             April 12, 2001


The Bank of Nova Scotia,
 as the U.S. Agent
One Liberty Plaza
New York, New York 10006

The Bank of Nova Scotia,
 as the Canadian Agent
44 King Street West -- 14th Floor
Toronto, Ontario
Canada, M5H 1H1

Each of the Lenders party to the
 Credit Agreement referred to below


                        THIRD AMENDMENT TO WAIVER LETTER

Gentlemen and Ladies:

     We refer to (a) the Amended and Restated Credit Agreement, dated as of
May 15, 1998 (as further amended, supplemented, amended and restated or
otherwise modified prior to the date hereof, the "CREDIT AGREEMENT"), among
Leiner Health Products Inc., a Delaware corporation (the "U.S. BORROWER"),
Vita Health Products Inc., a Manitoba corporation (the "CANADIAN BORROWER",
and together with the U.S. Borrower, the "BORROWERS"), the various financial
institutions as are or may become parties thereto which extend a Commitment
under the U.S. Facility (collectively, the "U.S. LENDERS"), the various
financial institutions as are or may become parties thereto which extend a
Commitment under the Canadian Facility (collectively, the "CANADIAN LENDERS",
and together with the U.S. Lenders, the "LENDERS"), The Bank of Nova Scotia
("SCOTIABANK") as agent for the U.S. Lenders under the U.S. Facility (in
such capacity, the "U.S. AGENT"), Scotiabank, as agent for the Canadian
Lenders under the Canadian Facility (in such capacity, the "CANADIAN AGENT",
and together with the U.S. Agent, collectively, the "AGENTS"), Merrill Lynch
Capital Corporation, as Documentation Agent, and Salomon Brothers Holding
Company Inc., as Syndication Agent, and (b) the Waiver Letter, dated February
13, 2001 (the "WAIVER LETTER"), from the Borrowers to the Agents and the
Lenders (as amended by the Amendment to Waiver Letter, dated February 23,
2001, and the Second Amendment to Waiver Letter, dated March 28, 2001).
Unless otherwise defined in this Third Amendment to Waiver Letter (this

<PAGE>

"AMENDMENT") or the context otherwise requires, terms used in this Amendment
have the meanings provided in the Credit Agreement or the Waiver Letter, as
applicable.

     The Borrowers hereby request that the Required Lenders amend the Waiver
Letter by extending the waiver termination date set forth in clause (x) of
the second paragraph of the Waiver Letter from April 12, 2001 to June 15,
2001 (the "WAIVER TERMINATION DATE").

     In consideration of the Lenders' delivery of this Amendment, the
Borrowers agree that they will, and will cause their Subsidiaries to, comply
with the following covenants:

     1.   Promptly and in any event no later than 4:00 p.m. on (i) May 15,
          2001, the Borrowers will deliver to Casas, Benjamin & White a draft
          of the Business Plan (as defined below), and (ii) May 22, 2001, the
          Borrowers will deliver to each Lender a final completed business plan
          (the "BUSINESS PLAN") which, in each case of (i) and (ii) will be in
          form and scope satisfactory to the Agents and consistent with the
          outline to be mutually agreed upon by Casas, Benjamin & White and
          Alvaraz & Marsal.

     2.   The Borrowers (and their representatives and management) will meet
          with the Lenders on May 30, 2001 in either Carson, California or New
          York, New York to, among other things, discuss the Business Plan,
          and the Borrowers will, no later than May 11, 2001, inform the
          Agents of the exact time and location of such meeting.

     3.   Unless otherwise agreed to by the Required Lenders, including as to
          amount and application, during the period from and after the date of
          this Amendment to (and including) the Waiver Termination Date,
          concurrently with the receipt by either Borrower or any of their
          Affiliates of any judgement, settlement or other proceeds or amounts,
          however characterized, arising from or in connection with any
          anti-trust claims (including the Anti-trust Litigation, with all of
          the foregoing collectively referred to as the "PROCEEDS"), the U.S.
          Borrower shall make, or cause to be made, a mandatory prepayment of
          the Loans in the amount of the Proceeds, to be applied PRO RATA to
          the outstanding principal amount of all Loans (with the amount of
          such prepayment being applied to the remaining Term Loan
          amortization payments PRO RATA in accordance with the amount of each
          such remaining Term Loan amortization payment) and the cash
          collaterization of all Letters of Credit and a corresponding
          reduction of each Revolving Loan Commitment Amount.

     4.   As soon as available and in any event no later than May 15, 2001 (in
          the case of the month ending March 31, 2001) and thereafter as soon
          as available and in any event within 21 days after the end of each
          month, the Canadian Borrower will deliver to the Canadian Agent
          consolidated and consolidating balance sheets of the Canadian
          Borrower and it Subsidiaries as of the end of such month and


                                          -2-

<PAGE>
          consolidated statements of earnings and cash flow of the Canadian
          Borrower and its Subsidiaries for such month and for the period
          commencing at the end of the previous Fiscal Year and ending with the
          last day of such month. The Canadian Borrower agrees that this
          covenant shall survive termination or expiration of this Amendment
          and the Waiver Letter.

     Furthermore, the Borrowers acknowledge and agree that (i) the covenants
set forth in numbers 2 and 6 of the third paragraph of the Waiver Letter and
the increased interest accrual set forth in clause (b)(iii) of the fourth
paragraph of the Waiver Letter shall each continue to (and including) the
Waiver Termination Date, (ii) notwithstanding the terms of the Credit
Agreement to the contrary , the U.S. Borrower and its U.S. Subsidiaries will
not, directly or indirectly, make any Investments (including intercompany
loans or capital contributions) in or to the Canadian Borrower or any of the
Canadian Borrower's Subsidiaries, or sell, transfer, lease, contribute or
otherwise convey (including by way of merger), or grant options, warrants or
other rights (all collectively referred to as a "DISPOSITION") with respect
to all or any part of their assets to the Canadian Borrower or any of the
Canadian Borrower's Subsidiaries and (iii) notwithstanding the terms of the
Credit Agreement to the contrary, the Canadian Borrower and its Subsidiaries
will not, directly or indirectly, make any Investments (including
intercompany loans or capital contributions) in or to (or pay dividends or
make distributions to) the U.S. Borrower or any of the U.S. Borrower's U.S.
Subsidiaries, or make any Disposition with respect to all or any part of
their assets to the U.S. Borrower or any of the U.S Borrower's U.S.
Subsidiaries, other than, in each case, in the ordinary course of business
consistent with past practices, and the Borrowers agree that the terms of
clauses (ii) and (iii) of this sentence shall survive termination or
expiration of the terms of this Amendment (and may only be amended, waived or
otherwise modified with the consent of the Canadian Lenders and the Required
Lenders).

     The Lenders hereby agree that the Borrowers may provide the weekly
rolling cash flow forecasts for each 13 week period, together with an actual
to forecast variance analysis for the preceding week, reflecting revisions
which have been approved by representatives of Casas, Benjamin & White
without breaching the requirements set forth in number 2 of the third
paragraph of the Waiver Letter; PROVIDED that the requirements of number 6 of
the third paragraph of the Waiver Letter continue to be in effect. In
addition, the Lenders hereby agree that the requirements of number 6 of the
third paragraph of the Waiver Letter will not be breached as a result of the
payment of any fees and expenses of Mayer, Brown & Platt required as a
condition to the effectiveness of this Amendment to the extent such fees and
expenses were not included in the Initial Forecast for the week in which they
are paid.

     In order to induce the Lenders to enter into this Amendment, the
Borrowers hereby represent and warrant that, both before and after giving
effect to this Amendment, all of the statements set forth in Section 7.2.1.
of the Credit Agreement are true and correct.

     This Amendment shall become effective upon (a) the receipt by the U.S.
Agent of executed counterparts hereof by the Borrowers and the Required
Lenders, (b) receipt by the U.S. Agent, for the account of each Lender, of a
waiver fee in an amount equal to $375,000 (which

                                      -3-
<PAGE>

shall be non-refundable and earned in full on the effectiveness of this
Amendment), payable to each Lender PRO RATA in accordance with such Lender's
Percentage of the Total Exposure Amount as of the date hereof, (c) payment of
all fees and expenses of Mayer, Brown & Platt, counsel to the U.S. Agent, and
(d) the Borrowers depositing with (i) the U.S. Agent, in the case of interest
that will accrue on the Credit Extensions under the U.S. Facility, an amount
in immediately available funds equal to $6,488,944.69 (representing interest
on the Credit Extensions under the U.S. Facility for April, May and June,
2001, calculated based on the Alternate Base Rate as in effect on the date
hereof) and (ii) the Canadian Agent, in the case of interest that will accrue
on the Credit Extensions under the Canadian Facility, an amount in
immediately available funds equal to Cdn $1,063,120.68 (representing interest
on the Credit Extensions under the Canadian Facility for April, May and June,
2001, calculated based on the Canadian Prime Rate as in effect on the date
hereof), to be held in escrow on terms satisfactory to the U.S. Agent or the
Canadian Agent, as applicable, and to be applied by the U.S. Agent or the
Canadian Agent, as applicable, to the payment of interest on the applicable
Credit Extensions in accordance with clause (c) of Section 5.2.3 of the
Credit Agreement for each of April, May and June, 2001. This Amendment may be
executed by the parties hereto in several counterparts, each of which shall
be an original and all of which shall constitute together but one and the
same agreement. Delivery of an executed counterpart of a signature page to
this Amendment by facsimile shall be effective as delivery of a manually
executed counterpart of this Amendment.

     THIS AMENDMENT SHALL BE GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH,
THE INTERNAL LAWS OF THE STATE OF NEW YORK.
Except as expressly modified by this Amendment, all of the terms and
provisions of the Waiver Letter ( and the amendments thereto, dated February
23, 2001 and March 28, 2001, respectively), the Credit Agreement and the
other Loan Documents shall remain in full force and effect. This Amendment is
a Loan Document executed pursuant to the Credit Agreement and shall be
construed and administrated in accordance with all of the terms and
provisions of the Credit Agreement.



                                     -4-
<PAGE>

     If you are in agreement with the foregoing terms, kindly execute this
Amendment in the space provided below and deliver to the Agents an executed
counterpart of this Amendment.


                                       Very truly yours,

                                       LEINER HEALTH PRODUCTS INC.


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



                                       VITA HEALTH PRODUCTS INC.


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






                                     -5-
<PAGE>


AGREED TO AND ACCEPTED
AS OF THE DATE FIRST
ABOVE WRITTEN:



--------------------------------
[NAME OF LENDER]


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










                                     -6-
<PAGE>