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                                                                     Exhibit 3.1


                           CERTIFICATE OF DESIGNATIONS

                                       OF

                  SERIES A JUNIOR PARTICIPATING PREFERRED STOCK

                                       OF

                                  SEPRACOR INC.

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

Sepracor Inc., a corporation organized and existing under the laws of the State
of Delaware (hereinafter called the "Corporation"), hereby certifies that the
following resolution was adopted by the Board of Directors of the Corporation at
a meeting duly called and held on June 3, 2002:

RESOLVED: That pursuant to the authority granted to and vested in the Board of
Directors of the Corporation (hereinafter called the "Board") in accordance with
the provisions of the Certificate of Incorporation, as amended, the Board hereby
creates a series of Preferred Stock, $1.00 par value per share (the "Preferred
Stock"), of the Corporation and hereby states the designation and number of
shares, and fixes the relative rights, preferences and limitations thereof as
follows:

     SERIES A JUNIOR PARTICIPATING PREFERRED STOCK:

     Section 1. DESIGNATION AND AMOUNT. The shares of such series shall be
designated as "Series A Junior Participating Preferred Stock" (the "Series A
Preferred Stock") and the number of shares constituting the Series A Preferred
Stock shall be two hundred forty thousand (240,000). Such number of shares may
be increased or decreased by resolution of the Board prior to issuance;
provided, that no decrease shall reduce the number of shares of Series A
Preferred Stock to a number less than the number of shares then outstanding plus
the number of shares reserved for issuance upon the exercise of outstanding
options, rights or warrants or upon the conversion of any outstanding securities
issued by the Corporation convertible into Series A Preferred Stock.

     Section 2. DIVIDENDS AND DISTRIBUTIONS.

     (A) Subject to the rights of the holders of any shares of any series of
Preferred Stock (or any similar stock) ranking prior and superior to the Series
A Preferred Stock with respect to dividends, the holders of shares of Series A
Preferred Stock, in preference to the holders of Common Stock, par value $0.10
per share (the "Common Stock"), of the Corporation, and of any other junior
stock, shall be entitled to receive, when, as and if declared by the Board out
of funds of the Corporation legally available for the payment of dividends,
quarterly dividends payable in cash on the last day of each fiscal quarter of
the Corporation in each year (each such date being


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referred to herein as a "Quarterly Dividend Payment Date"), commencing on the
first Quarterly Dividend Payment Date after the first issuance of a share or
fraction of a share of Series A Preferred Stock, in an amount per share (rounded
to the nearest cent) equal to the greater of (a) $10 or (b) subject to the
provision for adjustment hereinafter set forth, 1000 times the aggregate per
share amount of all cash dividends, and 1000 times the aggregate per share
amount (payable in kind) of all non-cash dividends or other distributions, other
than a dividend payable in shares of Common Stock or a subdivision of the
outstanding shares of Common Stock (by reclassification or otherwise), declared
on the Common Stock since the immediately preceding Quarterly Dividend Payment
Date or, with respect to the first Quarterly Dividend Payment Date, since the
first issuance of any share or fraction of a share of Series A Preferred Stock.
In the event the Corporation shall at any time declare or pay any dividend on
the Common Stock payable in shares of Common Stock, or effect a subdivision,
combination or consolidation of the outstanding shares of Common Stock (by
reclassification or otherwise than by payment of a dividend in shares of Common
Stock) into a greater or lesser number of shares of Common Stock, then in each
such case the amount to which holders of shares of Series A Preferred Stock were
entitled immediately prior to such event under clause (b) of the preceding
sentence shall be adjusted by multiplying such amount by a fraction, the
numerator of which is the number of shares of Common Stock outstanding
immediately after such event and the denominator of which is the number of
shares of Common Stock that were outstanding immediately prior to such event. In
the event the Corporation shall at any time declare or pay any dividend on the
Series A Preferred Stock payable in shares of Series A Preferred Stock, or
effect a subdivision, combination or consolidation of the outstanding shares of
Series A Preferred Stock (by reclassification or otherwise than by payment of a
dividend in shares of Series A Preferred Stock) into a greater or lesser number
of shares of Series A Preferred Stock, then in each such case the amount to
which holders of shares of Series A Preferred Stock were entitled immediately
prior to such event under clause (b) of the first sentence of this Section 2(A)
shall be adjusted by multiplying such amount by a fraction, the numerator of
which is the number of shares of Series A Preferred Stock that were outstanding
immediately prior to such event and the denominator of which is the number of
shares of Series A Preferred Stock outstanding immediately after such event.

     (B) The Corporation shall declare a dividend or distribution on the Series
A Preferred Stock as provided in paragraph (A) of this Section immediately after
it declares a dividend or distribution on the Common Stock (other than a
dividend payable in shares of Common Stock) and the Corporation shall pay such
dividend or distribution on the Series A Preferred Stock before the dividend or
distribution declared on the Common Stock is paid or set apart; provided that,
in the event no dividend or distribution shall have been declared on the Common
Stock during the period between any Quarterly Dividend Payment Date and the next
subsequent Quarterly Dividend Payment Date, a dividend of $10 per share on the
Series A Preferred Stock shall nevertheless be payable on such subsequent
Quarterly Dividend Payment Date.

     (C) Dividends shall begin to accrue and be cumulative on outstanding shares
of Series A Preferred Stock from the Quarterly Dividend Payment Date next
preceding the date of issue of such shares, unless the date of issue of such
shares is prior to the record date for the first Quarterly Dividend Payment
Date, in which case dividends on such shares shall begin to accrue from the date
of issue of such shares, or unless the date of issue is a Quarterly Dividend
Payment Date or is a date after the record date for the determination of holders
of shares of Series A


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Preferred Stock entitled to receive a quarterly dividend and before such
Quarterly Dividend Payment Date, in either of which events such dividends shall
begin to accrue and be cumulative from such Quarterly Dividend Payment Date.
Accrued but unpaid dividends shall not bear interest. Dividends paid on the
shares of Series A Preferred Stock in an amount less than the total amount of
such dividends at the time accrued and payable on such shares shall be allocated
pro rata on a share-by-share basis among all such shares at the time
outstanding. The Board may fix a record date for the determination of holders of
shares of Series A Preferred Stock entitled to receive payment of a dividend or
distribution declared thereon, which record date shall be not more than 60 days
prior to the date fixed for the payment thereof.

     Section 3. VOTING RIGHTS. The holders of shares of Series A Preferred Stock
shall have the following voting rights:

     (A) Subject to the provision for adjustment hereinafter set forth, each
share of Series A Preferred Stock shall entitle the holder thereof to 1000 votes
on all matters submitted to a vote of the stockholders of the Corporation. In
the event the Corporation shall at any time declare or pay any dividend on the
Common Stock payable in shares of Common Stock, or effect a subdivision,
combination or consolidation of the outstanding shares of Common Stock (by
reclassification or otherwise than by payment of a dividend in shares of Common
Stock) into a greater or lesser number of shares of Common Stock, then in each
such case the number of votes per share to which holders of shares of Series A
Preferred Stock were entitled immediately prior to such event shall be adjusted
by multiplying such number by a fraction, the numerator of which is the number
of shares of Common Stock outstanding immediately after such event and the
denominator of which is the number of shares of Common Stock that were
outstanding immediately prior to such event. In the event the Corporation shall
at any time declare or pay any dividend on the Series A Preferred Stock payable
in shares of Series A Preferred Stock, or effect a subdivision, combination or
consolidation of the outstanding shares of Series A Preferred Stock (by
reclassification or otherwise than by payment of a dividend in shares of Series
A Preferred Stock) into a greater or lesser number of shares of Series A
Preferred Stock, then in each such case the number of votes per share to which
holders of shares of Series A Preferred Stock were entitled immediately prior to
such event shall be adjusted by multiplying such amount by a fraction, the
numerator of which is the number of shares of Series A Preferred Stock that were
outstanding immediately prior to such event and the denominator of which is the
number of shares of Series A Preferred Stock outstanding immediately after such
event.

     (B) Except as otherwise provided herein, in the Certificate of
Incorporation or by law, the holders of shares of Series A Preferred Stock and
the holders of shares of Common Stock and any other capital stock of the
Corporation having general voting rights shall vote together as one class on all
matters submitted to a vote of stockholders of the Corporation.

     (C) If at any time dividends on any Series A Preferred Stock shall be in
arrears in an amount equal to six quarterly dividends thereon, the holders of
the Series A Preferred Stock, voting as a separate series from all other series
of Preferred Stock and classes of capital stock, shall be entitled to elect two
members of the Board in addition to any Directors elected by any other series,
class or classes of securities and the authorized number of Directors will
automatically be increased by two. Promptly thereafter, the Board of the
Corporation shall, as soon as may be practicable, call a special meeting of
holders of Series A Preferred Stock for the


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purpose of electing such members of the Board. Such special meeting shall in any
event be held within 45 days of the occurrence of such arrearage.

          (i) During any period when the holders of Series A Preferred Stock,
voting as a separate series, shall be entitled and shall have exercised their
right to elect two Directors, then, and during such time as such right
continues, (a) the then authorized number of Directors shall be increased by
two, and the holders of Series A Preferred Stock, voting as a separate series,
shall be entitled to elect the additional Directors so provided for, and (b)
each such additional Director shall not be a member of any existing class of the
Board, but shall serve until the next annual meeting of stockholders for the
election of Directors, or until his successor shall be elected and shall
qualify, or until his right to hold such office terminates pursuant to the
provisions of this Section 3(C).

          (ii) A Director elected pursuant to the terms hereof may be removed
with or without cause by the holders of Series A Preferred Stock entitled to
vote in an election of such Director.

          (iii) If, during any interval between annual meetings of stockholders
for the election of Directors and while the holders of Series A Preferred Stock
shall be entitled to elect two Directors, there is no such Director in office by
reason of resignation, death or removal, then, promptly thereafter, the Board
shall call a special meeting of the holders of Series A Preferred Stock for the
purpose of filling such vacancy and such vacancy shall be filled at such special
meeting. Such special meeting shall in any event be held within 45 days of the
occurrence of such vacancy.

          (iv) At such time as the arrearage is fully cured, and all dividends
accumulated and unpaid on any shares of Series A Preferred Stock outstanding are
paid, and, in addition thereto, at least one regular dividend has been paid
subsequent to curing such arrearage, the term of office of any Director elected
pursuant to this Section 3(C), or his successor, shall automatically terminate,
and the authorized number of Directors shall automatically decrease by two, the
rights of the holders of the shares of the Series A Preferred Stock to vote as
provided in this Section 3(C) shall cease, subject to renewal from time to time
upon the same terms and conditions, and the holders of shares of the Series A
Preferred Stock shall have only the limited voting rights elsewhere herein set
forth.

     (D) Except as set forth herein, or as otherwise provided by law, holders of
Series A Preferred Stock shall have no special voting rights and their consent
shall not be required (except to the extent they are entitled to vote with
holders of Common Stock as set forth herein) for taking any corporate action.

     Section 4. CERTAIN RESTRICTIONS.

     (A) Whenever quarterly dividends or other dividends or distributions
payable on the Series A Preferred Stock as provided in Section 2 are in arrears,
thereafter and until all accrued and unpaid dividends and distributions, whether
or not declared, on shares of Series A Preferred Stock outstanding shall have
been paid in full, the Corporation shall not:


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               (i) declare or pay dividends, or make any other distributions, on
          any shares of stock ranking junior (either as to dividends or upon
          liquidation, dissolution or winding up) to the Series A Preferred
          Stock;

               (ii) declare or pay dividends, or make any other distributions,
          on any shares of stock ranking on a parity (either as to dividends or
          upon liquidation, dissolution or winding up) with the Series A
          Preferred Stock, except dividends paid ratably on the Series A
          Preferred Stock and all such parity stock on which dividends are
          payable or in arrears in proportion to the total amounts to which the
          holders of all such shares are then entitled;

               (iii) redeem or purchase or otherwise acquire for consideration
          shares of any stock ranking junior (either as to dividends or upon
          liquidation, dissolution or winding up) to the Series A Preferred
          Stock, provided that the Corporation may at any time redeem, purchase
          or otherwise acquire shares of any such junior stock in exchange for
          shares of any stock of the Corporation ranking junior (either as to
          dividends or upon dissolution, liquidation or winding up) to the
          Series A Preferred Stock; or

               (iv) redeem or purchase or otherwise acquire for consideration
          any shares of Series A Preferred Stock, or any shares of stock ranking
          on a parity with the Series A Preferred Stock, except in accordance
          with a purchase offer made in writing or by publication (as determined
          by the Board) to all holders of such shares upon such terms as the
          Board, after consideration of the respective annual dividend rates and
          other relative rights and preferences of the respective series and
          classes, shall determine in good faith will result in fair and
          equitable treatment among the respective series or classes.

     (B) The Corporation shall not permit any subsidiary of the Corporation to
purchase or otherwise acquire for consideration any shares of stock of the
Corporation unless the Corporation could, under paragraph (A) of this Section 4,
purchase or otherwise acquire such shares at such time and in such manner.

     Section 5. REACQUIRED SHARES. Any shares of Series A Preferred Stock
purchased or otherwise acquired by the Corporation in any manner whatsoever
shall be retired and cancelled promptly after the acquisition thereof. All such
shares shall upon their cancellation become authorized but unissued shares of
Preferred Stock and may be reissued as part of a new series of Preferred Stock
subject to the conditions and restrictions on issuance set forth herein, in the
Certificate of Incorporation, or in any other Certificate of Designations
creating a series of Preferred Stock or any similar stock or as otherwise
required by law.

     Section 6. LIQUIDATION, DISSOLUTION OR WINDING UP.

     (A) Upon any liquidation, dissolution or winding up of the Corporation, no
distribution shall be made (1) to the holders of shares of stock ranking junior
(either as to dividends or upon liquidation, dissolution or winding up) to the
Series A Preferred Stock unless, prior thereto, the holders of shares of Series
A Preferred Stock shall have received $1000 per


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share, plus an amount equal to accrued and unpaid dividends and distributions
thereon, whether or not declared, to the date of such payment, provided that the
holders of shares of Series A Preferred Stock shall be entitled to receive an
aggregate amount per share, subject to the provision for adjustment hereinafter
set forth, equal to 1000 times the aggregate amount to be distributed per share
to holders of shares of Common Stock, or (2) to the holders of shares of stock
ranking on a parity (either as to dividends or upon liquidation, dissolution or
winding up) with the Series A Preferred Stock, except distributions made ratably
on the Series A Preferred Stock and all such parity stock in proportion to the
total amounts to which the holders of all such shares are entitled upon such
liquidation, dissolution or winding up.

     (B) Neither the consolidation, merger or other business combination of the
Corporation with or into any other corporation nor the sale, lease, exchange or
conveyance of all or any part of the property, assets or business of the
Corporation shall be deemed to be a liquidation, dissolution or winding up of
the Corporation for purposes of this Section 6.

     (C) In the event the Corporation shall at any time declare or pay any
dividend on the Common Stock payable in shares of Common Stock, or effect a
subdivision, combination or consolidation of the outstanding shares of Common
Stock (by reclassification or otherwise than by payment of a dividend in shares
of Common Stock) into a greater or lesser number of shares of Common Stock, then
in each such case the aggregate amount to which holders of shares of Series A
Preferred Stock were entitled immediately prior to such event under the proviso
in clause (1) of paragraph (A) of this Section 6 shall be adjusted by
multiplying such amount by a fraction, the numerator of which is the number of
shares of Common Stock outstanding immediately after such event and the
denominator of which is the number of shares of Common Stock that were
outstanding immediately prior to such event. In the event the Corporation shall
at any time declare or pay any dividend on the Series A Preferred Stock payable
in shares of Series A Preferred Stock, or effect a subdivision, combination or
consolidation of the outstanding shares of Series A Preferred Stock (by
reclassification or otherwise than by payment of a dividend in shares of Series
A Preferred Stock) into a greater or lesser number of shares of Series A
Preferred Stock, then in each such case the aggregate amount to which holders of
shares of Series A Preferred Stock were entitled immediately prior to such event
under the proviso in clause (1) of paragraph (A) of this Section 6 shall be
adjusted by multiplying such amount by a fraction, the numerator of which is the
number of shares of Series A Preferred Stock that were outstanding immediately
prior to such event and the denominator of which is the number of shares of
Series A Preferred Stock outstanding immediately after such event.

     Section 7. CONSOLIDATION, MERGER, ETC. Notwithstanding anything to the
contrary contained herein, in case the Corporation shall enter into any
consolidation, merger, combination or other transaction in which the shares of
Common Stock are exchanged for or changed into other stock or securities, cash
and/or any other property, then in any such case each share of Series A
Preferred Stock shall at the same time be similarly exchanged or changed into an
amount per share, subject to the provision for adjustment hereinafter set forth,
equal to 1,000 times the aggregate amount of stock, securities, cash and/or any
other property (payable in kind), as the case may be, into which or for which
each share of Common Stock is changed or exchanged. In the event the Corporation
shall at any time declare or pay any dividend on the Common Stock payable in
shares of Common Stock, or effect a subdivision, combination or consolidation of
the outstanding shares of Common Stock (by reclassification or otherwise than


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by payment of a dividend in shares of Common Stock) into a greater or lesser
number of shares of Common Stock, then in each such case the amount set forth in
the preceding sentence with respect to the exchange or change of shares of
Series A Preferred Stock shall be adjusted by multiplying such amount by a
fraction, the numerator of which is the number of shares of Common Stock
outstanding immediately after such event and the denominator of which is the
number of shares of Common Stock that were outstanding immediately prior to such
event. In the event the Corporation shall at any time declare or pay any
dividend on the Series A Preferred Stock payable in shares of Series A Preferred
Stock, or effect a subdivision, combination or consolidation of the outstanding
shares of Series A Preferred Stock (by reclassification or otherwise than by
payment of a dividend in shares of Series A Preferred Stock) into a greater or
lesser number of shares of Series A Preferred Stock, then in each such case the
amount set forth in the first sentence of this Section 7 with respect to the
exchange or change of shares of Series A Preferred Stock shall be adjusted by
multiplying such amount by a fraction, the numerator of which is the number of
shares of Series A Preferred Stock that were outstanding immediately prior to
such event and the denominator of which is the number of shares of Series A
Preferred Stock outstanding immediately after such event.

     Section 8. NO REDEMPTION. The shares of Series A Preferred Stock shall not
be redeemable.

     Section 9. RANK. The Series A Preferred Stock shall rank, with respect to
the payment of dividends and the distribution of assets, junior to all series of
any other class of the Preferred Stock issued either before or after the
issuance of the Series A Preferred Stock, unless the terms of any such series
shall provide otherwise.

     Section 10. AMENDMENT. At such time as any shares of Series A Preferred
Stock are outstanding, the Certificate of Incorporation, as amended, of the
Corporation shall not be amended in any manner which would materially alter or
change the powers, preferences or special rights of the Series A Preferred Stock
so as to affect them adversely without the affirmative vote of the holders of at
least two-thirds of the outstanding shares of Series A Preferred Stock, voting
together as a single class.

     Section 11. FRACTIONAL SHARES. Series A Preferred Stock may be issued in
fractions of a share which shall entitle the holder, in proportion to such
holder's fractional shares, to exercise voting rights, receive dividends,
participate in distributions and have the benefit of all other rights of holders
of Series A Preferred Stock.

IN WITNESS WHEREOF, this Certificate of Designations is executed on behalf of
the Corporation by its Executive Vice President, Finance and Administration and
Treasurer this 3rd day of June, 2002.

                                  SEPRACOR INC.

                                  By:  /s/ Robert F. Scumaci
                                       ---------------------
                                  Name:    Robert F. Scumaci
                                  Title:   Executive Vice President, Finance and
                                  Administration and Treasurer


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