<PAGE>   1
                                                                    EXHIBIT 4.3

Large Corporate
Unsecured Demand Note

                         DEMAND MASTER PROMISSORY NOTE
                              (Money Market Rate)

$30,000,000                                                     Cleveland, Ohio
                                                                  June 20, 1997



        On demand, Borrower promises to pay to the order of Bank, at any of its
offices, the unpaid principal amount of each Advance, together with interest
(calculated on the basis of a year of 360 days for the actual number of days
elapsed) on the daily unpaid principal balance of such Advance from the date
upon which such Advance is made at a rate per annum equal to the Interest Rate
applicable to such Advance payable on the earlier of (1) the date of demand of
payment of such Advance, or (2) the Interest Period Termination Date of such
Advance. After the earlier of demand or the Interest Period Termination Date of
any Advance, the unpaid principal and accrued interest of each such Advance
shall, until paid, bear interest at a rate per annum equal to the Default
Interest Rate. In no event shall the interest rate hereon exceed the highest
rate permitted by law.

        The aggregate unpaid principal amount of all loan Advances pursuant to
this line facility shall not at any one time exceed Thirty Million Dollars
($30,000,000). No Advance may be prepaid prior to the Interest Period
Termination Date applicable to such Advance without the prior written consent
of the Bank, except upon demand by the Bank. This note shall serve as a master
note to evidence all Advances. Bank's records as to (a) the principal amount,
the Interest Period Termination Date, and the Interest Rate applicable to each
Advance, and (b) each payment of principal and interest received by Bank
applicable to each Advance, shall be rebuttably presumed to be accurate.

        Borrower waives presentment, demand, notice, protest, and all other
demands and notices in connection with delivery, acceptance, performance,
default, or enforcement of this Note. Borrower understands and agrees that this
Note is subject to and shall be construed according to the laws of the State of
Ohio.

        Upon demand of payment of the Advances and at all times thereafter, at
the option of Bank, all sums owed hereunder shall become immediately due and
payable, in addition to any other rights and remedies Bank may have pursuant to
law, this Note, or any other instruments or agreements, which rights and
remedies shall be cumulative.

        No delay or omission on the part of Bank in exercising any right or
remedy hereunder or in connection herewith shall operate as a waiver of such
right or remedy or of any other right or remedy hereunder or in connection
herewith. Any waiver of Bank's rights or remedies hereunder or in connection
herewith must be in writing and signed by Bank. A waiver on any one occasion
shall not be construed as a bar to or waiver of any such right or remedy on a
future occasion.

<PAGE>   2
Large Corporate
Unsecured Demand Note



        In the event Borrower voluntarily repays or prepays any Advance, in
whole or in part, prior to the Interest Period Termination Date therefor, other
than as a result of a demand for payment by Bank hereunder, Borrower shall
reimburse Bank on demand for any resulting loss or expense incurred by Bank as
a result of such repayment or prepayment of such Advance including, without
limitation, any loss incurred in obtaining, liquidating, or employing deposits
from third parties, but excluding loss of margin on the amount of principal
repaid or prepaid for the period after any such repayment or prepayment.

        In the event Bank incurs, directly or indirectly, any additional cost
in making, maintaining or allocating capital to any Advance as a result of
complying with any charge, cost, reserve or other requirement imposed from time
to time by any United States regulatory agency or law or regulation applicable
to Bank, except for income taxes, Borrower will pay to Bank promptly upon
Bank's written notice such amount as in the reasonable judgment of Bank will
compensate it for such additional cost.

        Borrower represents that it has legal power and right to execute and
deliver this Note and to perform and observe the provisions of this Note. By
executing and delivering this Note and by performing and observing the
provisions of this Note, Borrower will not violate any existing provision of
its articles of incorporation, code of regulations or bylaws or any applicable
law or violate or otherwise become in default under any existing contract,
including any agreements for borrowed money or otherwise evidencing or relating
to any Indebtedness, or other obligation binding upon Borrower. The officer or
officers executing and delivering this Note on behalf of Borrower have been
duly authorized to do so, and this Note, when executed, is legally binding upon
Borrower in every respect.

        For the purposes of this Note:

        "ADVANCES" collectively means all loan advances made by Bank to Borrower
    at the sole discretion and option of the Bank. Borrower acknowledging that
    the line facility evidenced by this Note is purely discretionary and Bank
    may, without prior notice to Borrower refuses to honor any request by
    Borrower for borrowing hereunder, and "ADVANCE" means any of the Advances.

        "BANK" means KEYBANK NATIONAL ASSOCIATION, a national banking
    association with its main office located at 127 Public Square, Cleveland,
    Ohio 44114, and its successors and assigns.

        "BORROWER" means NCS HealthCare, Inc. and its successors and assigns;
    PROVIDED, HOWEVER, that Borrower may not assign or otherwise transfer any of
    its rights under this Note without the express written consent of Bank.

        "DEFAULT INTEREST RATE" means, as to any Advance, that fixed rate per
    annum (calculated on the basis of a year of 360 days for the actual number
    of days elapsed) equal to the Interest Rate plus two percent (2%) per annum.



                                      -2-
<PAGE>   3
Large Corporate
Unsecured Demand Note



        "INDEBTEDNESS" shall mean for any Person (i) all obligations to repay
    borrowed money, direct or indirect, incurred, assumed, or guaranteed, (ii)
    all obligations for the deferred purchase price of capital assets excluding
    trade payables, (iii) all obligations under conditional sales or other title
    retention agreements, and (iv) and all lease obligations which have been or
    should be capitalized on the books of such Person.

        "INTEREST RATE" means, as to any Advance, that fixed rate per annum
    determined by Bank and mutually agreed upon by Bank and Borrower.

        "INTEREST PERIOD TERMINATION DATE" means, as to any Advance, that date
    determined by Bank and mutually agreed upon by Bank and Borrower which is
    the last day of the period selected in order to determine the Interest Rate
    and which shall not be more than three months days from the date of such
    Advance.

        "PERSON" shall mean any natural person, corporation (which shall be
    deemed to include business trust), association, limited liability company,
    partnership, joint venture, political entity, or political subdivision
    thereof.

        BORROWER, TO THE EXTENT PERMITTED BY LAW, WAIVES ANY RIGHT TO HAVE A
JURY PARTICIPATE IN RESOLVING ANY DISPUTE, WHETHER SOUNDING IN CONTRACT, TORT,
OR OTHERWISE, BETWEEN BANK AND BORROWER ARISING OUT OF, IN CONNECTION WITH,
RELATED TO, OR INCIDENTAL TO THE RELATIONSHIP ESTABLISHED BETWEEN BORROWER AND
BANK IN CONNECTION WITH THIS NOTE OR ANY OTHER AGREEMENT, INSTRUMENT OR
DOCUMENT EXECUTED OR DELIVERED IN CONNECTION THEREWITH OR THE TRANSACTIONS
RELATED THERETO.

        IN WITNESS WHEREOF, BORROWER HAS DULY EXECUTED AND DELIVERED THIS NOTE
ON THE DATE FIRST ABOVE WRITTEN.

                                       BORROWER:


                                       NCS HealthCare, Inc.

                                       By: /s/Jeffrey R. Steinhilber
                                          --------------------------
                                              Jeffrey R. Steinhilber
                                              Senior Vice President and
                                              Chief Financial Officer