<Page>
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                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

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

                                  FORM 10-Q/A

                               AMENDMENT NO. 1 TO
                                   FORM 10-Q

(MARK ONE)

<Table>
<C>        <S>
   /X/     QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE
           SECURITIES EXCHANGE ACT OF 1934
</Table>

               FOR THE QUARTERLY PERIOD ENDED: SEPTEMBER 30, 2001

                                       OR

<Table>
<C>        <S>
   / /     TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE
           SECURITIES EXCHANGE ACT OF 1934
</Table>

        FOR THE TRANSITION PERIOD FROM ______________ TO ______________

                         COMMISSION FILE NUMBER 0-19410

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

                                 SEPRACOR INC.
             (Exact name of registrant as specified in its charter)

<Table>
<S>                                       <C>
             DELAWARE                                 22-2536587
 (State or Other Jurisdiction of          (IRS Employer Identification No.)
  Incorporation or Organization)

         111 LOCKE DRIVE,
    MARLBOROUGH, MASSACHUSETTS                          01752
      (Address of Principal                           (zip code)
        Executive Offices)
</Table>

       Registrant's telephone number, including area code: (508) 481-6700
        Securities registered pursuant to Section 12(b) of the Act: NONE
          Securities registered pursuant to Section 12(g) of the Act:

                          COMMON STOCK, $.10 PAR VALUE
                                (Title of class)

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

    Indicate by check mark whether the registrant: (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports) and (2) has been subject to such
filing requirements for the past 90 days. Yes /X/ No / /

    Number of shares outstanding of the registrant's class of Common Stock as of
November 5, 2001: 77,913,562 shares.

--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
<Page>
                                EXPLANATORY NOTE

    This Amendment No. 1 on Form 10-Q/A to the Registrant's Quarterly Report on
Form 10-Q for the quarter ended September 30, 2001 is being filed to reflect the
Registrant's private placement of $400,000,000 of 5 3/4% Convertible
Subordinated Notes due 2006, which is expected to close on November 14, 2001. In
addition, this Amendment No. 1 is being filed to include the conformed signature
pages to the Registrant's Quarterly Report on Form 10-Q, which were
unintentionally omitted from the initial filing. The Registrant's Quarterly
Report on Form 10-Q is hereby amended and restated in its entirety as follows:

                                       2
<Page>
                                 SEPRACOR INC.
                                     INDEX

<Table>
<S>       <C>                                                           <C>
PART I--FINANCIAL INFORMATION

Item 1.   Consolidated Condensed Financial Statements

          Consolidated Condensed Balance Sheets as of September 30,
          2001 and December 31, 2000 (Unaudited)......................      4

          Consolidated Statements of Operations for the Three and Nine
          Months Ended September 30, 2001 and 2000 (Unaudited)........      5

          Consolidated Statements of Cash Flows for the Nine Months
          Ended September 30, 2001 and 2000 (Unaudited)...............      6

          Notes to Consolidated Interim Financial Statements..........      7

Item 2.   Management's Discussion and Analysis of Financial Condition
          and Results of Operations...................................     11

Item 3.   Quantitative and Qualitative Disclosures About Market
          Risk........................................................     25

PART II--OTHER INFORMATION

Item 1.   Legal Proceedings...........................................     25

Signatures............................................................     26
</Table>

                                       3
<Page>
                                 SEPRACOR INC.
                     CONSOLIDATED CONDENSED BALANCE SHEETS
                                  (UNAUDITED)
                                 (IN THOUSANDS)

<Table>
<Caption>
                                                              SEPTEMBER 30, 2001   DECEMBER 31, 2000
                                                              ------------------   -----------------
<S>                                                           <C>                  <C>
ASSETS
Current assets:
Cash and cash equivalents...................................       $ 313,131           $ 354,058
Short-term investments......................................         142,767             248,818
Accounts receivable, net....................................          20,699              14,756
Inventories.................................................           7,078               5,998
Other current assets........................................          10,772               5,212
                                                                   ---------           ---------
Total current assets........................................         494,447             628,842

Long-term investments.......................................          23,333              31,603
Property and equipment, net.................................          24,436              22,676
Investment in Versicor......................................          24,243              13,746
Equity investment in related parties........................           7,244                  --
Patents, intangible assets and other assets, net............          55,010              54,091
                                                                   ---------           ---------
Total assets................................................       $ 628,713           $ 750,958
                                                                   =========           =========
LIABILITIES AND STOCKHOLDERS' EQUITY (DEFICIT)
Current liabilities:
Accounts payable............................................       $   6,652           $  30,665
Accrued expenses............................................          70,423              65,560
Notes payable, current portion of long-term debt
  and capital lease obligation..............................             628                 144
Other current liabilities...................................          16,330               7,810
                                                                   ---------           ---------
Total current liabilities...................................          94,033             104,179

Convertible subordinated debentures.........................         759,960             852,818
Long-term debt and capital lease obligation.................           1,569               1,098
Other long-term liabilities.................................              --                 478
                                                                   ---------           ---------
Total liabilities...........................................         855,562             958,573

Minority interest...........................................              --               7,059

Stockholders' equity (deficit):
Preferred stock.............................................              --                  --
Common stock................................................           7,787               7,383
Additional paid-in capital..................................         559,691             461,195
Unearned compensation, net..................................            (137)               (189)
Accumulated deficit.........................................        (815,133)           (693,387)
Accumulated other comprehensive income......................          20,943              10,324
                                                                   ---------           ---------
Total stockholders' equity (deficit)........................        (226,849)           (214,674)
                                                                   ---------           ---------
Total liabilities and stockholders' equity (deficit)........       $ 628,713           $ 750,958
                                                                   =========           =========
</Table>

   THE ACCOMPANYING NOTES ARE AN INTEGRAL PART OF THE CONSOLIDATED FINANCIAL
                                   STATEMENTS

                                       4
<Page>
                                 SEPRACOR INC.
                     CONSOLIDATED STATEMENTS OF OPERATIONS
                                  (UNAUDITED)
                    (IN THOUSANDS, EXCEPT PER SHARE AMOUNTS)

<Table>
<Caption>
                                                 THREE MONTHS ENDED               NINE MONTHS ENDED
                                            -----------------------------   -----------------------------
                                            SEPTEMBER 30,   SEPTEMBER 30,   SEPTEMBER 30,   SEPTEMBER 30,
                                                2001            2000            2001            2000
                                            -------------   -------------   -------------   -------------
<S>                                         <C>             <C>             <C>             <C>
Revenues:
  Product sales...........................    $ 31,574        $ 10,179        $  93,039       $  33,680
  Collaborative research and
    development...........................          --              --               --           3,573
  License fees............................          --              --               --          20,000
  Royalties and other.....................       5,118           1,304           21,803           3,615
                                              --------        --------        ---------       ---------
    Total revenues........................      36,692          11,483          114,842          60,868

Costs and expenses:
  Cost of product sold....................       3,228           2,262           11,938           7,786
  Cost of license fees....................          --              --               --           2,000
  Cost of royalties and other.............          --             272              493             849
  Research and development................      56,981          34,968          154,227         105,480
  Selling, general and administrative and
    patent costs..........................      29,488          24,062           82,646          69,643
                                              --------        --------        ---------       ---------
    Total costs and expenses..............      89,697          61,564          249,304         185,758
                                              --------        --------        ---------       ---------
Loss from operations......................     (53,005)        (50,081)        (134,462)       (124,890)

Other income (expense):
  Interest income.........................       5,229          11,683           21,013          30,872
  Interest expense........................     (11,017)        (12,467)         (33,772)        (35,286)
  Other income (expense), net.............          48              70            1,022          (7,336)
  Gain on sale of subsidiary stock........      23,113              --           23,113              --
  Equity in investee gains (losses).......        (812)          4,490             (812)          3,501
                                              --------        --------        ---------       ---------
Net loss before minority interest.........     (36,444)        (46,305)        (123,898)       (133,139)

Minority interest in subsidiary...........          --           1,079            2,152           2,568
                                              --------        --------        ---------       ---------
Net loss..................................    $(36,444)       $(45,226)       $(121,746)      $(130,571)
                                              ========        ========        =========       =========

Basic and diluted net loss per common
  share...................................    $  (0.47)       $  (0.62)       $   (1.57)      $   (1.80)

Shares used in computing basic and diluted
  net loss per common share:
Basic and diluted.........................      77,866          73,334           77,390          72,435
</Table>

   THE ACCOMPANYING NOTES ARE AN INTEGRAL PART OF THE CONSOLIDATED FINANCIAL
                                   STATEMENTS

                                       5
<Page>
                                 SEPRACOR INC.
                     CONSOLIDATED STATEMENTS OF CASH FLOWS
                                  (UNAUDITED)
                                 (IN THOUSANDS)

<Table>
<Caption>
                                                                         NINE MONTHS ENDED
                                                              ---------------------------------------
                                                              SEPTEMBER 30, 2001   SEPTEMBER 30, 2000
                                                              ------------------   ------------------
<S>                                                           <C>                  <C>
Cash flows from operating activities:
Net loss....................................................      $(121,746)           $(130,571)
Adjustments to reconcile net loss to net cash used in
  operating activities:
  Depreciation and amortization.............................          9,519                8,322
  Minority interest in subsidiary...........................         (2,152)              (2,568)
  Provision for bad debt....................................            145                   60
  Gain on sale of subsidiary stock..........................        (23,113)                  --
  Equity in investee (gains) losses.........................            812               (3,501)
  Deferred compensation.....................................             --                1,195
  Loss on disposal of property and equipment................            198                   25
Changes in operating assets and liabilities:
  Accounts receivable.......................................         (7,757)              (3,409)
  Inventories...............................................         (1,887)              (2,022)
  Other current assets......................................         (5,801)                 707
  Accounts payable..........................................        (22,931)              (7,080)
  Accrued expenses..........................................          7,028               11,967
  Other current liabilities.................................          8,520                2,512
                                                                  ---------            ---------
Net cash used in operating activities.......................       (159,165)            (124,363)
                                                                  ---------            ---------
Cash flows from investing activities:
  Purchases of short and long-term investments..............       (357,532)            (690,385)
  Sales and maturities of short and long-term investments...        471,957              553,518
  Net proceeds from Sepracor's sale of BioSphere stock......         26,604                   --
  Deconsolidation of BioSphere cash.........................         (9,405)                  --
  Purchase of intangible assets.............................             --              (12,500)
  Investment in subsidiary..................................             --               (5,000)
  Additions to property and equipment.......................         (7,594)              (5,060)
  Change in other assets....................................         (8,808)              (1,798)
                                                                  ---------            ---------
Net cash provided by (used in) investing activities.........        115,222             (161,225)
                                                                  ---------            ---------
Cash flows from financing activities:
  Net proceeds from issuance of common stock................          2,023               28,066
  Net proceeds from BioSphere issuance of common stock......              9               18,092
  Proceeds from sale of 5% convertible subordinated
    debentures..............................................             --              460,000
  Costs associated with sale of 5% convertible subordinated
    debentures..............................................             --              (14,033)
  Repayments of long-term debt, capital leases and line of
    credit agreements.......................................           (395)                 (40)
  Borrowings of long-term debt, capital leases and line of
    credit agreements.......................................          1,475                   45
                                                                  ---------            ---------
Net cash provided by financing activities...................          3,112              492,130
                                                                  ---------            ---------
Effect of exchange rate changes on cash and cash
  equivalents...............................................            (96)                 218
                                                                  ---------            ---------
Net increase (decrease) in cash and cash equivalents........        (40,927)             206,760

Cash and cash equivalents at beginning of period............      $ 354,058            $  59,488
                                                                  ---------            ---------
Cash and cash equivalents at end of period..................      $ 313,131            $ 266,248
                                                                  =========            =========
Non cash activities:
  Conversion of convertible subordinated debentures to
    shares of common stock..................................      $  92,858            $  96,632
</Table>

   THE ACCOMPANYING NOTES ARE AN INTEGRAL PART OF THE CONSOLIDATED FINANCIAL
                                   STATEMENTS

                                       6
<Page>
               NOTES TO CONSOLIDATED INTERIM FINANCIAL STATEMENTS

1.  BASIS OF PRESENTATION:

    The accompanying consolidated interim financial statements are unaudited and
have been prepared on a basis substantially consistent with the audited
financial statements. Certain information and footnote disclosures normally
included in Sepracor's annual financial statements have been condensed or
omitted. The year-end consolidated condensed balance sheet data was derived from
audited financial statements but does not include all disclosures required by
generally accepted accounting principles. The consolidated interim financial
statements, in the opinion of management, reflect all adjustments (including
normal recurring accruals) necessary for a fair presentation of the results for
the interim periods ended September 30, 2001 and 2000.

    The consolidated results of operations for the interim periods are not
necessarily indicative of the results of operations to be expected for the
fiscal year. These consolidated interim financial statements should be read in
conjunction with the audited financial statements for the year ended December
31, 2000, which are contained in Sepracor's Annual Report on Form 10-K for the
year ended December 31, 2000, filed with the Securities and Exchange Commission.

    The consolidated financial statements include the accounts of Sepracor Inc.
("Sepracor" or the "Company") and its majority and wholly-owned subsidiaries,
including BioSphere Medical Inc. ("BioSphere", which was majority owned through
July 2, 2001) and Sepracor Canada Limited. The consolidated financial statements
also include equity ownership in Sepracor's related parties HemaSure Inc.
("HemaSure") and BioSphere (effective July 3, 2001), and an investment in
Versicor Inc. ("Versicor").

2.  SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES:

a) NEW ACCOUNTING PRONOUNCEMENTS

    In June 2000, the Financial Accounting Standards Board ("FASB") issued
Statement of Financial Accounting Standards ("SFAS") No. 138, "Accounting for
Certain Derivative Instruments"--an amendment of SFAS No. 133 ("Accounting for
Certain Derivative Instruments and Hedging Activities"). This statement
establishes accounting and reporting standards for derivative instruments
embedded in other contracts (collectively referred to as "derivatives"), and for
hedging activities. The statement requires companies to recognize all
derivatives as either assets or liabilities, with the instruments measured at
fair value. The accounting for changes in fair value, gains or losses, depends
on the intended use of the derivative and its resulting designation. The Company
has adopted SFAS No. 138 in 2001, in accordance with SFAS No.137, which deferred
the effective date of SFAS No. 133. The adoption of SFAS No. 138 did not have a
material impact on the Company's financial statements and related disclosures.

    In June 2001, the FASB issued SFAS No. 141 "business combinations" which
addresses financial accounting and reporting for business combinations. All
business combinations initiated after June 30, 2001, in the scope of SFAS No.
141, are to be accounted for using one method, the purchase method. SFAS No. 141
also requires that certain acquired intangible assets in a business combination
be recognized as assets apart from goodwill. The Company notes that SFAS No. 141
does not currently have any effect on the reported financial results.

    In June 2001, the FASB issued SFAS No. 142 "Goodwill and Other Intangible
Assets" which addresses how intangible assets that are acquired individually or
with a group of other assets (but not those acquired in a business combination)
should be accounted for in financial statements upon their acquisition. The
statement also addresses how goodwill and other intangible assets should be
accounted for after they have been initially recognized in the financial
statements. The provisions of the statement are required to be applied starting
with fiscal years beginning after December 15, 2001. Sepracor will

                                       7
<Page>
review other intangible assets and adopt the provisions of the statement
beginning on January 1, 2002. The adoption of this standard is not expected to
have a material impact on the Company's financial statements and related
disclosures.

b) ACCOUNTING POLICIES--ROYALTY REVENUE

    The Company receives royalty revenues under license agreements with various
third parties that sell products based on technology developed by the Company or
to which the Company has rights. The license agreements provide for the payment
of royalties to the Company based on sales of the licensed product. The Company
records these revenues based on estimates of the sales that occurred during the
relevant period. The relevant period estimates of sales are based on third party
data and analysis of historical royalties paid to the Company (adjusted for any
changes in facts and circumstances, as appropriate). The Company maintains
regular communication with its licensees in order to gauge the reasonableness of
its estimates. Differences between actual royalty revenues and estimated royalty
revenues are reconciled and adjusted for in the following quarter. Historically,
adjustments have not been material.

c) BASIC AND DILUTED NET (LOSS) PER COMMON SHARE

    Basic earnings (loss) per share ("EPS") excludes dilution and is computed by
dividing income available to common shareholders by the weighted-average number
of common shares outstanding for the period. Diluted EPS is based upon the
weighted average number of common shares outstanding during the period plus the
additional weighted average common equivalent shares during the period. Common
equivalent shares are not included in the per share calculations where the
effect of their inclusion would be anti-dilutive. Common equivalent shares
result from the assumed conversion of preferred stock, convertible subordinated
debentures and the assumed exercises of outstanding stock options, the proceeds
of which are then assumed to have been used to repurchase outstanding stock
options using the treasury stock method.

    For the three and nine months ended September 30, 2001 and 2000, basic and
diluted net loss per common share is computed based on the weighted-average
number of common shares outstanding during the period because the effect of
common stock equivalents would be anti-dilutive. Certain securities were not
included in the computation of diluted earnings per share for the three and nine
months ended September 30, 2001 and 2000 because they would have an
anti-dilutive effect due to net losses for such periods. These securities
include the following:

    Options to purchase shares of common stock:

<Table>
<Caption>
(IN THOUSANDS, EXCEPT PRICE PER SHARE DATA)      SEPTEMBER 30, 2001   SEPTEMBER 30, 2000
-------------------------------------------      ------------------   ------------------
<S>                                              <C>                  <C>
Number of options..............................             10,781                9,591
Price range per share..........................   $2.50 to $125.44     $1.50 to $125.44
</Table>

    Shares of common stock for issuance upon conversion of convertible
subordinated debentures:

<Table>
<Caption>
(IN THOUSANDS)                                    SEPTEMBER 30, 2001   SEPTEMBER 30, 2000
--------------                                    ------------------   ------------------
<S>                                               <C>                  <C>
6 1/4% convertible subordinated debentures
  due 2005......................................            --                3,922
7% convertible subordinated debentures
  due 2005......................................         4,804                4,804
5% convertible subordinated debentures
  due 2007......................................         4,979                4,979
                                                    ----------           ----------
                                                         9,783               13,705
</Table>

                                       8
<Page>
3.  INVENTORIES, NET:

    Inventories consist of the following:

<Table>
<Caption>
(IN THOUSANDS)                                    SEPTEMBER 30, 2001   DECEMBER 31, 2000
--------------                                    ------------------   -----------------
<S>                                               <C>                  <C>
Raw materials...................................        $    8              $2,322
Work in progress................................         3,109                 432
Finished goods..................................         3,961               3,244
                                                        ------              ------
                                                        $7,078              $5,998
</Table>

4.  CONVERTIBLE SUBORDINATED DEBENTURES:

<Table>
<Caption>
(IN THOUSANDS)                                    SEPTEMBER 30, 2001   DECEMBER 31, 2000
--------------                                    ------------------   -----------------
<S>                                               <C>                  <C>
6 1/4% convertible subordinated debentures
  due 2005(1)...................................       $     --            $ 92,858
7% convertible subordinated debentures
  due 2005......................................        299,960             299,960
5% convertible subordinated debentures
  due 2007......................................        460,000             460,000
                                                       --------            --------
                                                       $759,960            $852,818
</Table>

(1) In February 2001, the Company converted $92,858,000 in principal amount of
    6 1/4% convertible subordinated debentures due 2005 into 3,920,608 shares of
    Sepracor Common Stock. As a result of the transaction, deferred finance
    costs of approximately $1,525,000 were written off against additional
    paid-in capital.

5.  COMPREHENSIVE INCOME (LOSS):

    Total comprehensive income (loss) is comprised of net income (loss), net
currency translation adjustments, and unrealized gain (loss) on
available-for-sale securities.

<Table>
<Caption>
                                                 THREE MONTHS ENDED               NINE MONTHS ENDED
                                            -----------------------------   -----------------------------
                                            SEPTEMBER 30,   SEPTEMBER 30,   SEPTEMBER 30,   SEPTEMBER 30,
(IN THOUSANDS)                                  2001            2000            2001            2000
--------------                              -------------   -------------   -------------   -------------
<S>                                         <C>             <C>             <C>             <C>
Comprehensive income (loss):
  Net loss................................    $(36,444)       $(45,226)       $(121,746)      $(130,571)
  Cumulative translation adjustment.......          62             159               19             219
  Unrealized gain on available-for-sale
    securities............................       1,626          20,865           10,600          20,919
                                              --------        --------        ---------       ---------
Total comprehensive income (loss).........    $(34,756)       $(24,202)       $(111,127)      $(109,433)
                                              ========        ========        =========       =========
</Table>

6.  INVESTMENT IN VERSICOR AND RELATED PARTIES:

INVESTMENT IN VERSICOR:

    Sepracor considers its investment in Versicor as an available-for-sale
security and as such has marked-to-market its investment at the September 28,
2001 market price, which resulted in the recording of an unrealized gain of
approximately $10,497,000 as a separate component of stockholders' equity for
the nine months ended September 30, 2001.

                                       9
<Page>
RELATED PARTIES:

    In February 2001, HemaSure signed an asset purchase agreement with Whatman
plc. Under the terms of the agreement, Whatman agreed to purchase HemaSure's
assets, except for cash, cash equivalents and marketable securities of HemaSure,
subject to certain exceptions as defined in the agreement. On May 29, 2001,
HemaSure completed the sale to Whatman Bioscience Inc., a Massachusetts
corporation and a subsidiary of Whatman plc. The transaction was approved by
HemaSure's stockholders at a special meeting of stockholders on May 21, 2001.
The Company's investment in HemaSure is recorded at zero.

    In July 2001, Sepracor announced that it had sold 2,000,000 shares of
BioSphere common stock held by it in a public offering in which BioSphere also
sold 2,000,000 shares of its common stock at a price to the public of $11.00 per
share. On August 2, 2001, the underwriters exercised their over-allotment option
to purchase an additional 600,000 shares of BioSphere common stock from Sepracor
at a price to the public of $11.00 per share. Sepracor received net proceeds,
after offering costs, from the sales of approximately $26,604,000 and has
recognized a gain of approximately $23,113,000 in the three months ended
September 30, 2001. As a result of the public offering, Sepracor's ownership in
BioSphere has been reduced from approximately 55% to 25% as of September 30,
2001. Sepracor no longer consolidates BioSphere and now records its investment
in BioSphere under the equity method, effective July 3, 2001. Sepracor has
recorded $812,000 as its share of BioSphere losses for the three months ended
September 30, 2001.

7.  LITIGATION:

    Currently Sepracor is not a party to any material legal proceedings.

8.  SUBSEQUENT EVENT:

    On November 8, 2001, Sepracor announced the private placement of
$400,000,000 of 5 3/4% Convertible Subordinated Notes due 2006 (the "5 3/4%
Notes"). The offering, which was made through an initial purchaser to qualified
institutional buyers under Rule 144A of the Securities Act of 1933, as amended
is expected to close on November 14, 2001.

    The 5 3/4% Notes are convertible into Sepracor common stock, at the option
of the holder, at a price of $60.00 per share. The 5 3/4% Notes bear interest at
5 3/4% payable semiannually, commencing on May 15, 2002. The 5 3/4% Notes are
redeemable by the Company prior to maturity if the closing price of Sepracor
common stock exceeds 145% of the conversion price ($87.00) for at least 20 out
of 30 consecutive trading days ending within five trading days prior to notice
of automatic conversion. The Company may be required to repurchase the 5 3/4%
Notes at the option of the holders in certain circumstances. As part of the sale
of the 5 3/4% Notes, Sepracor expects to incur offering costs of approximately
$11,600,000 which will be recorded as other assets and will be amortized over
five years, the term of the 5 3/4% Notes. Sepracor has granted the initial
purchaser a 45-day option to purchase an additional $100 million in aggregate
principal amount of 5 3/4% Notes.

    The net proceeds to the Company after offering costs are expected to be
$388,400,000 (assuming the initial purchaser does not exercise the option).

                                       10
<Page>
                                    ITEM 2.
          MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION
                           AND RESULTS OF OPERATIONS

    This Quarterly Report on Form 10-Q contains, in addition to historical
information, forward-looking statements within the meaning of Section 21E of the
Securities Exchange Act of 1934, as amended. These forward-looking statements
involve risk and uncertainties and are not guarantees of future performance.
Sepracor's actual results could differ significantly from the results discussed
in such forward-looking statements. See "Factors Affecting Future Operating
Results" below.

OVERVIEW

    Sepracor Inc. is a research-based pharmaceutical company dedicated to
treating and preventing human disease through the discovery, development, and
commercialization of innovative pharmaceutical products that are directed toward
serving unmet medical needs. Sepracor's drug development program has yielded an
extensive portfolio of pharmaceutical candidates that are focused on the
treatment of respiratory, urological, and central nervous system disorders.
Sepracor's corporate headquarters are located in Marlborough, Massachusetts.

    The consolidated financial statements include the accounts of Sepracor Inc.
("Sepracor", the "Company" or "We") and its majority and wholly-owned
subsidiaries, including BioSphere Medical Inc. ("BioSphere", which was majority
owned through July 2, 2001) and Sepracor Canada Limited. The consolidated
financial statements also include equity ownership in Sepracor's related parties
HemaSure Inc. ("HemaSure") and BioSphere (effective July 3, 2001), and an
investment in Versicor Inc. ("Versicor").

    In May 1999, Sepracor introduced XOPENEX-Registered Trademark- brand
levalbuterol HCl, a single isomer of the bronchodilator albuterol. XOPENEX is
the first pharmaceutical product developed and commercialized by Sepracor.

    On November 8, 2001, Sepracor announced the private placement of
$400,000,000 of 5 3/4% Convertible Subordinated Notes due 2006 (the "5 3/4%
Notes"). The offering, which was made through an initial purchaser to qualified
institutional buyers under Rule 144A of the Securities Act of 1933, as amended
is expected to close on November 14, 2001.

    The 5 3/4% Notes are convertible into Sepracor common stock, at the option
of the holder, at a price of $60.00 per share. The 5 3/4% Notes bear interest at
5 3/4% payable semiannually, commencing on May 15, 2002. The 5 3/4% Notes are
redeemable by the Company prior to maturity if the closing price of Sepracor
common stock exceeds 145% of the conversion price ($87.00) for at least 20 out
of 30 consecutive trading days ending within five trading days prior to notice
of automatic conversion. The Company may be required to repurchase the 5 3/4%
Notes at the option of the holders in certain circumstances. As part of the sale
of the 5 3/4% Notes, Sepracor expects to incur offering costs of approximately
$11,600,000 which will be recorded as other assets and will be amortized over
five years, the term of the 5 3/4% Notes. Sepracor has granted the initial
purchaser a 45-day option to purchase an additional $100 million in aggregate
principal amount of 5 3/4% Notes. The net proceeds to the Company after offering
costs are expected to be $388,400,000 (assuming the initial purchaser does not
exercise the option).

    Sepracor intends to file with the United States Food and Drug Administration
(the "FDA") a New Drug Application (an "NDA") for esopiclone, which, if
approved, would be marketed under the name ESTORRA. The NDA for esopiclone will
include a preclinical, clinical and postmarketing surveillance data package
relating to zopiclone and its isomers and metabolites that the Company licensed
from Rhone-Poulenc Rorer SA. On October 26, 2001, the Company had a pre-NDA
meeting with the FDA at which there was discussion concerning the completeness
of the data package. If the FDA determines

                                       11
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that the data package is insufficient to support the proposed NDA submission, it
may refuse to accept the NDA for filing or require the Company to conduct
additional studies. While the Company believes that there should not be
significant delays in the filing of the NDA, there can be no assurance that the
Company will not be required to conduct additional studies, that any such
studies will produce results satisfactory to the FDA or that significant delays
in the commercialization of esopiclone, will not occur.

    In July 2001, Sepracor announced that it had sold 2,000,000 shares of
BioSphere common stock held by it in a public offering in which BioSphere also
sold 2,000,000 shares of its common stock at a price to the public of $11.00 per
share. On August 2, 2001, the underwriters exercised their over-allotment option
to purchase an additional 600,000 shares of BioSphere common stock from Sepracor
at a price to the public of $11.00 per share. Sepracor received net proceeds,
after offering costs, from the sales of approximately $26,604,000 and has
recognized a gain of approximately $23,113,000 in the three months ended
September 30, 2001. As a result of the public offering, Sepracor's ownership in
BioSphere has been reduced from approximately 55% to 25% as of September 30,
2001. Sepracor no longer consolidates BioSphere and now records its investment
in BioSphere under the equity method, effective July 3, 2001. Sepracor has
recorded $812,000 as its share of BioSphere losses for the three months ended
September 30, 2001.

    In May 2001, the Company announced that the FDA had accepted for review the
Company's NDA for SOLTARA-TM- brand tecastemizole (formerly norastemizole)
capsules for the treatment of allergic rhinitis, which the Company submitted in
March 2001.

    The Company has a license agreement with Janssen Pharmaceutica N.V., a
wholly-owned subsidiary of Johnson & Johnson ("Janssen") for the use of
ticalopride (formerly (+)-norcisapride) for the treatment of gastroesophageal
reflux disease ("GERD"). In April 2001, the Company was notified by Janssen that
clinical investigators were to be informed that two Phase II trials to evaluate
the efficacy and safety of ticalopride ((+)-norcisapride) in subjects with
symptoms of GERD, or gastroparesis, were being suspended pending further
analysis of a small number of adverse events reported in GERD and diabetic
patients. The Company continues to work with Johnson & Johnson to access the
data from the suspended Phase II trials of ticalopride.

    In February 2001, HemaSure signed an asset purchase agreement with Whatman
plc. Under the terms of the agreement, Whatman agreed to purchase HemaSure's
assets, except for cash, cash equivalents and marketable securities of HemaSure,
subject to certain exceptions as defined in the agreement. On May 29, 2001,
HemaSure completed the sale to Whatman Bioscience Inc., a Massachusetts
corporation and a subsidiary of Whatman plc. The transaction was approved by
HemaSure's stockholders at a special meeting of stockholders on May 21, 2001.

    In January 2001, the Company announced that on February 21, 2001 it would
redeem the $92,858,000 in principal amount of 6 1/4% convertible subordinated
debentures due 2005 (the "6 1/4 Debentures") that remained outstanding. On
February 20, 2001, prior to the redemption, all outstanding 6 1/4% Debentures
were converted. As a result of the conversion, 3,920,608 shares of Sepracor
Common Stock were issued and deferred financing costs of approximately
$1,525,000 were written off against additional paid-in capital.

    In January 2001, Sepracor signed a lease to occupy approximately 192,600
square feet of office and research and development space in a facility to be
built in Marlborough, Massachusetts. The lease has a term of 15 years, and will
begin on the occupancy date contingent upon the completion of the building,
expected to be June 2002. In addition, Sepracor has an option to lease two
additional buildings, totaling approximately 232,400 square feet, which may be
constructed on the same site in the future. Sepracor is financing the
construction of the first building through two interest bearing, secured loans
totaling up to approximately $27,000,000, loaned by Sepracor to the developer of
the site. Sepracor will have first right to purchase the entire property from
the developer beginning in June 2002 and extending through January 2004. The
developer has the right to require Sepracor to purchase

                                       12
<Page>
the site based on a contractual amount less the amount of any loans outstanding
from the developer to Sepracor, if Sepracor's cash and cash equivalents fall
below $137,000,000 before substantial completion of the building.

    For the remainder of 2001, the Company expects that it will incur increasing
operating expenses, primarily due to expansion of research and development
activities relating to development of the Company's portfolio of pharmaceuticals
and drug candidates, and also due to increasing sales and marketing and general
and administrative efforts required in preparation of the anticipated
commercialization of SOLTARA brand tecastemizole (formerly norastemizole) and to
further advance its drug development programs to commercialization.

THREE MONTH PERIODS ENDED SEPTEMBER 30, 2001 AND 2000

    Product revenues were $31,574,000 and $10,179,000 for the three months ended
September 30, 2001 and 2000, respectively. The increase for the three-month
period ended September 30, 2001 is due primarily to increased sales of XOPENEX.

    Royalties and other revenues were $5,118,000 and $1,304,000 for the three
months ended September 30, 2001 and 2000, respectively. The increase for the
three months ended September 30, 2001 is due primarily to the royalty agreement
with Aventis, under which Sepracor currently receives royalties on U.S. and
non-U.S. sales of ALLEGRA-Registered Trademark- in countries where Sepracor
holds issued patents on terfenadine carboxylate (also known as fexofenadine).
Sepracor began earning royalties on sales of ALLEGRA in the U.S. and Canada in
the first quarter of 2001. Prior to 2001, Sepracor was earning royalties
primarily in Europe, Japan and Australia.

    Cost of product sold, as a percentage of product sales, was approximately
10% and 22% for the three months ended September 30, 2001 and 2000,
respectively. The decrease for the three months ended September 30, 2001 was
primarily due to a credit in 2001 of approximately $1,100,000 resulting from the
reversal of a liability related to a third party manufacturing issue that was
favorably resolved and also to overall lower manufacturing costs as a percentage
of product sales in 2001 than in 2000.

    Research and development expenses were $56,981,000 and $34,968,000 for the
three months ended September 30, 2001 and 2000, respectively. The increase for
the three months ended September 30, 2001 is primarily due to increased costs
incurred from Phase III clinical study costs relating to esopiclone (formerly
(S)-zopiclone), which if approved by the FDA, would be marketed under the name
ESTORRA, and to costs relating to (S)-oxybutynin for the completion of Phase II
clinical studies and the initiation of Phase III clinical studies.

    Selling, general and administrative and patent expenses were $29,488,000 and
$24,062,000 for the three months ended September 30, 2001 and 2000,
respectively. Of the total, selling and marketing expenses were $25,075,000 and
$18,738,000 for the three months ended September 30, 2001 and 2000,
respectively. The increase for the three months ended September 30, 2001 is
primarily due to increased selling and marketing expenses as a result of the
increase in XOPENEX sales, and an increase in marketing costs relating to the
expected commercialization of SOLTARA in 2002.

    The net of interest income, interest (expense) and other income (expense)
was ($5,740,000) and ($714,000) for the three months ended September 30, 2001
and 2000, respectively. The increase in net expense for the three months ended
September 30, 2001 is primarily due to lower interest income in 2001, because
the cash available for investment was lower than in 2000 and the cash was
invested at lower interest rates.

    Equity in investee gains (losses) was ($812,000) and $4,490,000 for the
three months ended September 30, 2001 and 2000, respectively. The loss for the
three-month period ended September 30, 2001, represents the Company's portion of
BioSphere losses. The gain in the three-month period ended

                                       13
<Page>
September 30, 2000 is due primarily to the reversal of a $5,000,000 HemaSure
loan guarantee during the third quarter of 2000, partially offset by Sepracor's
portion of HemaSure losses.

    The gain of $23,113,000 on the sale of subsidiary stock resulted from the
Company's sale of 2,600,000 shares of BioSphere common stock in July 2001.

    Minority interest in subsidiary resulted in a decrease to consolidated net
loss of $0 and $1,079,000 for the three months ended September 30, 2001 and
2000, respectively. The fluctuation in minority interest is due to the
Sepracor's sale of 2,600,000 shares of BioSphere common stock, which resulted in
a reduction of its ownership in BioSphere from approximately 55% to 25% as of
September 30, 2001. Sepracor no longer consolidates BioSphere and now records
its investment in BioSphere under the equity method, effective July 3, 2001.

NINE MONTH PERIODS ENDED SEPTEMBER 30, 2001 AND 2000

    Product revenues were $93,039,000 and $33,680,000 for the nine months ended
September 30, 2001 and 2000, respectively. The increase for the nine months
ended September 30, 2001 is due primarily to increased sales of XOPENEX.

    Collaborative research and development revenues were $0 and $3,573,000 for
the nine months ended September 30, 2001 and 2000, respectively. The $3,573,000
in 2000 represents proceeds from an agreement under which we licensed to Lilly
technology related to (R)-fluoxetine (the "Lilly (R)-Fluoxetine Agreement"),
which terminated in October 2000.

    License fee revenues were $0 and $20,000,000 for the nine months ended
September 30, 2001 and 2000, respectively. The $20,000,000 in 2000 represents
initial milestone payments received under the Lilly (R)-Fluoxetine Agreement.

    Royalties and other revenues were $21,803,000 and $3,615,000 for the nine
months ended September 30, 2001 and 2000, respectively. The increase for the
nine months ended September 30, 2001 is due primarily to the royalty agreement
with Aventis, under which Sepracor currently receives royalties on U.S. and
non-U.S. sales of ALLEGRA-Registered Trademark- in countries where Sepracor
holds issued patents on terfenadine carboxylate (also known as fexofenadine).
Sepracor began earning royalties on sales of ALLEGRA in the U.S. and Canada in
the first quarter of 2001. Prior to 2001, Sepracor was earning royalties
primarily in Europe, Japan and Australia.

    Cost of product sold, as a percentage of product sales, was approximately
13% and 23% for the nine months ended September 30, 2001 and 2000, respectively.
The decrease in cost of product sold as a percentage of product sales for the
nine months ended September 30, 2001 was due to the inclusion in the nine months
ended September 30, 2000, of $2,766,000 of manufacturing costs, or 8% of product
sales, related to a third party manufacturing issue. Additionally, cost of
product sold for the nine months ended September 30, 2001, includes a credit of
approximately $2,200,000 resulting from the reversal of a liability related to a
third party manufacturing issue.

    Cost of license fee revenues were $0 and $2,000,000 for the nine months
ended September 30, 2001 and 2000, respectively. The $2,000,000 in the
nine-month period ended September 30, 2000 represents sublicense fees owed under
a license agreement with a third party pertaining to patents related to the
Lilly (R)-Fluoxetine Agreement.

    Research and development expenses were $154,227,000 and $105,480,000 for the
nine months ended September 30, 2001 and 2000, respectively. The increase for
the nine months ended September 30, 2001 is primarily due to increased costs
incurred from Phase III clinical study costs relating to esopiclone (formerly
(S)-zopiclone) and to costs relating to (S)-oxybutynin for the completion of
Phase II clinical studies and the initiation of Phase III clinical studies.

                                       14
<Page>
    Selling, general and administrative and patent expenses were $82,646,000 and
$69,643,000 for the nine months ended September 30, 2001 and 2000, respectively.
Of the total, selling and marketing expenses were $67,625,000 and $54,362,000
for the nine months ended September 30, 2001 and 2000, respectively. The
increase for the nine months ended September 30, 2001 is primarily due to
increased selling and marketing expenses as a result of the increase in XOPENEX
sales and increased marketing costs relating to the expected commercialization
of SOLTARA in 2002.

    The net of interest income, interest (expense) and other income (expense)
was ($11,737,000) and ($11,750,000) for the nine months ended September 30, 2001
and 2000, respectively. Interest income for the nine months ended September 30,
2001 decreased by ($9,859,000) due to a reduction of cash available for
investment and lower interest rates on investments held. Other expense for the
nine months ended September 30, 2000 included $7,497,000 relating to inducements
and other costs for the conversion of $96,424,000 of 6 1/4% Debentures. Interest
expense for the nine months ended September 30, 2001 decreased by approximately
$1,514,000 as a result of a reduction in the amount of convertible debt
outstanding in the nine months ended September 30, 2001 as compared to the same
period in the prior year.

    Equity in investee gains (losses) was ($812,000) and $3,501,000 for the nine
months ended September 30, 2001 and 2000, respectively. The loss in the
nine-month period ended September 30, 2001, represents the Company's portion of
BioSphere losses. The gain in the nine-month period ended September 30, 2000 is
due primarily to the reversal of a $5,000,000 HemaSure loan guarantee during the
third quarter of 2000, partially offset by Sepracor's portion of HemaSure
losses.

    The gain of $23,113,000 on the sale of subsidiary stock resulted from the
Company's sale of 2,600,000 shares of BioSphere common stock in July 2001.

    Minority interest in subsidiary resulted in a decrease to consolidated net
loss of $2,152,000 and $2,568,000 for the nine months ended September 30, 2001
and 2000, respectively. The fluctuation in minority interest is due to the
Sepracor's sale of 2,600,000 shares of BioSphere common stock, which resulted in
a reduction of its ownership in BioSphere from approximately 55% to 25% as of
September 30, 2001. Sepracor no longer consolidates BioSphere and now records
its investment in BioSphere under the equity method, effective July 3, 2001.

LIQUIDITY AND CAPITAL RESOURCES

    Cash and cash equivalents and short and long-term investments totaled
$479,231,000 at September 30, 2001, compared to $634,479,000 at December 31,
2000.

    The net cash used in operating activities for the nine months ended
September 30, 2001 was $159,165,000. The net cash used in operating activities
includes a net loss of $121,746,000 adjusted by non-cash charges of $10,674,000.
These charges were offset by the minority interest in subsidiary's net loss of
$2,152,000 and the gain on sale of subsidiary stock of $23,113,000. Accounts
receivable increased by $7,757,000 due to increased sales of XOPENEX. Other
current assets increased by $5,801,000 primarily due to increased royalty
receivables from Aventis related to ALLEGRA. Accounts payable decreased by
$22,931,000 due to the timing of cash disbursements. Accrued expenses increased
by $7,028,000 primarily due to higher research and development costs. Other
current liabilities increased by $8,520,000 primarily due to additional accruals
for product revenue rebates and return reserves as a result of increased XOPENEX
revenues.

    The net cash provided by investing activities for the nine months ended
September 30, 2001 was $115,222,000. Cash resulted from net sales and maturities
of short and long-term investments of $114,425,000. The deconsolidation of
BioSphere's cash balance decreased cash by $9,405,000 and the net proceeds from
Sepracor's sale of BioSphere stock increased cash by $26,604,000. The Company
made purchases of property and equipment of $7,594,000, and other assets
increased by $8,808,000

                                       15
<Page>
primarily due to the construction financing loan receivable from the developer
of the property to be leased by Sepracor upon its completion.

    The net cash provided by financing activities for the nine months ended
September 30, 2001 was $3,112,000. The Company received approximately $2,023,000
in proceeds from the issuance of common stock and had a net increase in capital
lease and debt activity of $1,080,000.

    In July 2001, Sepracor announced that it had sold 2,000,000 shares of
BioSphere common stock held by it in a public offering in which BioSphere also
sold 2,000,000 shares of its common stock at a price to the public of $11.00 per
share. On August 2, 2001, the underwriters exercised their over-allotment option
to purchase an additional 600,000 shares of BioSphere common stock from Sepracor
at a price to the public of $11.00 per share. Sepracor received net proceeds,
after offering costs, from the sales of approximately $26,604,000 and has
recognized a gain of approximately $23,113,000 in the three months ended
September 30, 2001. As a result of the public offering, Sepracor's ownership in
BioSphere has been reduced from approximately 55% to 25% as of September 30,
2001. Sepracor no longer consolidates BioSphere and now records its investment
in BioSphere under the equity method, effective July 3, 2001. Sepracor has
recorded $812,000 as its share of BioSphere losses for the three months ended
September 30, 2001.

    In January 2001, the Company announced that on February 21, 2001 it would
redeem the $92,858,000 in principal amount of 6 1/4% Debentures that remained
outstanding. On February 20, 2001, prior to the redemption, all outstanding
6 1/4% Debentures were converted. As a result of the conversion, Sepracor issued
3,920,608 shares of Common Stock and deferred financing costs of approximately
$1,525,000 were written off against additional paid-in capital.

    The Company believes its existing cash and the anticipated cash flow from
its current strategic alliances and operations will be sufficient to support
existing operations through 2002. Sepracor's actual future cash requirements,
however, will depend on many factors, including the progress of its preclinical,
clinical, and research programs, the number and breadth of these programs, the
costs associated with commercialization of the Company's products and products
under development, achievement of milestones under its strategic alliance
arrangements, sales of its products, acquisitions, its ability to establish and
maintain additional strategic alliances and licensing arrangements and the
progress of the Company's development efforts and the development efforts of its
strategic partners.

FACTORS AFFECTING FUTURE OPERATING RESULTS

    Certain of the information contained in this Quarterly Report on Form 10-Q,
including information with respect to the safety, efficacy and potential
benefits of the Company's drugs under development and the scope of patent
protection with respect to these products, the timing of the submission,
acceptance and approval of regulatory filings and information with respect to
the other plans and strategies for the Company's business and the business of
the subsidiaries and certain affiliates of the Company, consists of
forward-looking statements. The forward-looking statements contained in this
Quarterly Report on Form 10-Q represent our expectations as of the date of this
Quarterly Report on Form 10-Q. Subsequent events will cause our expectations to
change. However, while we may elect to update these forward-looking statements,
we specifically disclaim any intention or obligation to do so. Important factors
that could cause actual results to differ materially from the forward-looking
statements include the following:

WE HAVE NEVER BEEN PROFITABLE AND WE MAY NOT BE ABLE TO GENERATE REVENUES
SUFFICIENT TO ACHIEVE PROFITABILITY.

    We have not been profitable since inception, and it is possible that we will
not achieve profitability. We incurred net losses applicable to common shares on
a consolidated basis of approximately $121.7 million for the nine months ended
September 30, 2001, $204.0 million for the year ended

                                       16
<Page>
December 31, 2000 and $183.1 million for the year ended December 31, 1999. We
expect to continue to incur significant operating and capital expenditures. As a
result, we will need to generate significant revenues to achieve and maintain
profitability. We cannot assure you that we will achieve significant revenues or
that we will ever achieve profitability. Even if we do achieve profitability, we
cannot assure you that we can sustain or increase profitability on a quarterly
or annual basis in the future. If revenues grow more slowly than we anticipate
or if operating expenses exceed our expectations or cannot be adjusted
accordingly, our business, results of operations and financial conditions will
be materially and adversely affected.

IF WE OR OUR DEVELOPMENT PARTNERS ARE NOT SUCCESSFUL IN DEVELOPING AND
COMMERCIALIZING OUR PRINCIPAL PRODUCTS UNDER DEVELOPMENT, THEN OUR ABILITY TO
BECOME PROFITABLE WILL BE ADVERSELY AFFECTED.

    Our ability to achieve profitability will depend in large part on successful
commercialization of our initial products and successful development and
commercialization of principal products under development. Failure to
successfully commercialize our products and products under development by us and
our development partners may have a material adverse effect on our business. As
a result, our revenues will be adversely affected. We are entitled to receive
royalties on sales, if any, of desloratadine under the DCL Agreement with
Schering. In February 2001, Schering announced that it had been advised by the
U.S. Food and Drug Administration, which we refer to as the FDA, that current
good manufacturing practices deficiencies cited by the FDA would need to be
resolved prior to FDA approval of desloratadine. We are entitled to receive
royalties on sales, if any, of ticalopride under the Ticalopride Agreement with
Janssen. In April 2001, Janssen announced that it had suspended clinical trials
of ticalopride pending further analysis of a small number of adverse events
reported in patients. We do not know if or when desloratadine or ticalopride may
be approved, or the timing of commercialization of these compounds. In addition,
if other collaborative development arrangements are terminated or
commercialization efforts under those agreements are delayed or are
unsuccessful, then successful commercialization of our products under
development may be delayed or terminated, which could have a material adverse
effect on our business.

    In May 2001, an advisory panel to the FDA recommended that the FDA allow
certain popular allergy medications to be sold without a prescription. The FDA
may or may not accept the recommendation of the advisory panel. If the FDA
approves the sale of these allergy medications without prescription, our
business may be adversely affected because royalty revenues may be reduced and
the market for prescription drugs, including SOLTARA brand tecastemizole
(formerly norastemizole), may be adversely affected.

WE WILL BE REQUIRED TO EXPEND SIGNIFICANT RESOURCES FOR RESEARCH, DEVELOPMENT,
TESTING AND REGULATORY APPROVAL OF OUR DRUGS UNDER DEVELOPMENT AND THESE DRUGS
MAY NOT BE DEVELOPED SUCCESSFULLY.

    We develop and commercialize proprietary pharmaceutical products for the
primary care and specialty markets. Most of our drug candidates are still
undergoing clinical trials or are in the early stages of development. Our ICE
drugs may not provide greater benefits or fewer side effects than the original
versions of these drugs and our research efforts may not lead to the discovery
of new drugs with benefits over existing treatments or development of new
therapies. All of our drugs under development will require significant
additional research, development, preclinical and/or clinical testing,
regulatory approval and a commitment of significant additional resources prior
to their commercialization. Our potential products may not:

    - be developed successfully;

    - be proven safe and efficacious in clinical trials;

    - offer therapeutic or other improvements over comparable drugs;

                                       17
<Page>
    - meet applicable regulatory standards;

    - be capable of being produced in commercial quantities at acceptable costs;
      or

    - be successfully marketed.

IF WE FAIL TO ADEQUATELY PROTECT OUR INTELLECTUAL PROPERTY RIGHTS OR FACE A
CLAIM OF INTELLECTUAL PROPERTY INFRINGEMENT BY A THIRD PARTY, THEN WE COULD LOSE
VALUABLE INTELLECTUAL PROPERTY RIGHTS, BE LIABLE FOR SIGNIFICANT DAMAGES OR BE
PREVENTED FROM COMMERCIALIZING OUR PRODUCTS.

    Our success depends in part on our ability to obtain and maintain patents,
protect trade secrets and operate without infringing upon the proprietary rights
of others. In the absence of patent and trade secret protection, competitors may
adversely affect our business by independently developing and marketing
substantially equivalent products and technology and preventing us from
marketing our products. It is also possible that we could incur substantial
costs in litigation if we are required to defend ourselves in patent suits
brought by third parties, or if we are required to initiate litigation against
others to protect our intellectual property rights.

    We have filed patent applications covering composition of, methods of making
and methods of using, single-isomer or active-metabolic forms of various
compounds for specific applications. Our revenues under collaboration agreements
with pharmaceutical companies depend in part on the existence and scope of
issued patents. However, we may not be issued patents based on the patent
applications already filed or that we file in the future, and if patents are
issued, they may be insufficient in scope to cover the products licensed under
these collaboration agreements. Moreover, the patent position of companies in
the pharmaceutical industry generally involves complex legal and factual
questions, and recently has been the subject of much litigation. Legal standards
relating to the scope and validity of patent claims are evolving. Any patents we
have obtained, or obtain in the future may be challenged, invalidated or
circumvented. Moreover, the United States Patent and Trademark Office, which we
refer to as the PTO, may commence interference proceedings involving our patents
or patent applications. Any challenge to, or invalidation or circumvention of,
our patents or patent applications could have a material adverse effect on our
business.

    Our ability to commercialize any drug successfully will largely depend upon
our ability to obtain and maintain patents of sufficient scope to prevent third
parties from developing similar or competitive products. Third parties,
typically drug companies, hold patents or patent applications covering the
composition of matter for most of the drug candidates for which we have use
patents or patent applications covering compositions, methods of making and
uses. Third parties also hold patents relating to drug delivery technology that
may be necessary for the development of some of our drug candidates. In each of
these cases, unless we have or obtain a license agreement, we generally may not
commercialize the drug candidates until these third party patents expire.
Licenses may not be available to us on acceptable terms, if at all. In addition,
it would be costly for us to contest the validity of a third party patent or
defend any claim that we infringe a third party patent. Moreover, litigation
involving third party patents may not be resolved in our favor. Such contests
and litigation may have a material adverse effect on our business.

IF OUR PRODUCTS DO NOT RECEIVE GOVERNMENT APPROVAL, THEN WE WILL NOT BE ABLE TO
COMMERCIALIZE THEM.

    The FDA, and similar foreign agencies, must approve the marketing and sale
of pharmaceutical products developed by us or our development partners. These
agencies impose substantial requirements on the manufacture and marketing of
drugs. In addition, although many of our development programs rely on existing
third-party data to support regulatory approvals, there can be no assurance that
the FDA or similar foreign agencies will deem the existing data adequate to
support approval of our product candidates. The FDA may require us to undertake
unanticipated or additional preclinical and clinical studies before they accept
for filing, or approve, any application filed by us. Any unanticipated

                                       18
<Page>
preclinical and clinical studies we are required to undertake could result in a
significant delay in commercialization or an increase in the funds we will
require to advance our products to commercialization. In addition, the failure
by us or our collaborative development partners to obtain regulatory approval on
a timely basis or, the attempt by us or our collaborative development partners
to receive regulatory approval to achieve labeling objectives, could adversely
affect the timing of the commercial introduction of, or our ability to market
and sell, our products. We are entitled to receive royalties on sales, if any,
of desloratadine under the DCL Agreement with Schering. In February 2001,
Schering announced that it had been advised by the FDA that current good
manufacturing practices deficiencies cited by the FDA would need to be resolved
prior to FDA approval of desloratadine. We do not know if or when the product
may be approved, or the timing of commercialization of desloratadine.

    We intend to file an NDA for esopiclone, which, if approved, would be
marketed under the name ESTORRA. Our NDA for esopiclone will include a
preclinical, clinical and postmarketing surveillance data package relating to
zopiclone and its isomers and metabolites that we licensed from Rhone-Poulenc
Rorer SA. On October 26, 2001, we had a pre-NDA meeting with the FDA at which
there was discussion concerning the completeness of the data package. If the FDA
determines that the data package is insufficient to support our proposed NDA
submission, it may refuse to accept our NDA for filing or require us to conduct
additional studies. While we believe that there should not be significant delays
in our filing of the NDA, there can be no assurance that we will not be required
to conduct additional studies, that any such studies will produce results
satisfactory to the FDA or that we will not incur significant delays in the
commercialization of esopiclone.

THE REGULATORY PROCESS TO OBTAIN MARKETING APPROVAL REQUIRES CLINICAL TRIALS OF
A PRODUCT TO ESTABLISH ITS SAFETY AND EFFICACY.

    Problems that may arise during clinical trials include:

    - results of clinical trials may not be consistent with preclinical study
      results;

    - results from later phases of clinical trials may not be consistent with
      the results from earlier phases; and

    - products may not be shown to be safe and efficacious.

    Even if the FDA or similar foreign agencies grant us regulatory approval of
a product, the approval may take longer than we anticipate and may be subject to
limitations on the indicated uses for which the product may be marketed or
contain requirements for costly post-marketing follow-up studies. Moreover, if
we fail to comply with applicable regulatory requirements, we may be subject to
fines, suspension or withdrawal of regulatory approvals, product recalls,
seizure of products, operating restrictions and criminal prosecution.

THE DEVELOPMENT AND COMMERCIALIZATION OF OUR PRODUCTS COULD BE DELAYED OR
TERMINATED IF OUR COLLABORATION PARTNERS TERMINATE, SUSPEND ACTIVITY OR FAIL TO
PERFORM THEIR OBLIGATIONS UNDER THEIR AGREEMENTS WITH US OR IF ANY OF OUR
COLLABORATION AGREEMENTS IS SUBJECT TO LENGTHY GOVERNMENT REVIEW.

    We have entered into collaboration arrangements with pharmaceutical
companies. Our revenues under these collaboration arrangements will consist
primarily of royalties on sales of products. Any such payments and royalties
will depend in large part on the development and commercialization efforts of
our collaboration partners, which we cannot control. If any of our collaboration
partners does not devote sufficient time and resources to, or suspends activity
under, its collaboration arrangement with us, we may not realize the potential
commercial benefits of the arrangement, and our results of operations may be
adversely affected. In addition, if regulatory approval of any product candidate
under development by our collaboration partners is delayed or limited, we may
not realize or may be

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delayed in realizing the potential commercial benefits of the arrangement. If
any of our collaboration partners was to breach or terminate its agreement with
us or fail to perform its obligations to us in a timely manner, the development
and commercialization of the products could be delayed or terminated. Any
failure or inability by us to perform, or any breach by us in our performance
of, our obligations under a collaboration agreement could reduce or extinguish
the benefits to which we are otherwise entitled under the agreement. Any delay
or termination of this type could have a material adverse effect on our
financial condition and results of operations because we may be required to
expend additional funds to bring our products to commercialization, we may lose
technology rights and milestone or royalty payments from collaboration partners
or revenue from product sales, if any, could be delayed or terminated. We are
entitled to receive royalties on sales, if any, of ticalopride under the
Ticalopride Agreement with Janssen, in countries where we have issued patents
covering Janssen's intended use. In April 2001, Janssen announced that it had
suspended clinical trials of ticalopride pending further analysis of a small
number of adverse events reported in patients.

    Development and commercialization of some of our product candidates may
depend on our ability to enter into additional collaboration agreements with
pharmaceutical companies to fund all or part of the costs of development and
commercialization of these product candidates. We may not be able to enter into
collaboration agreements and the terms of the collaboration agreements, if any,
may not be favorable to us. The inability to enter into collaboration agreements
could delay or preclude the development, manufacture and/or marketing of some of
our drugs and could have a material adverse effect on our financial condition
and results of operations because:

    - we may be required to expend additional funds to advance the drugs to
      commercialization;

    - revenues from product sales could be delayed; or

    - we may elect not to commercialize the drugs.

    We are required to file a notice under the Hart-Scott-Rodino Antitrust
Improvements Act of 1976, as amended, which we refer to as the HSR Act, for
certain agreements containing exclusive license grants and to delay the
effectiveness of any such exclusive license until the expiration or earlier
termination of the notice and waiting period under the HSR Act. If the
expiration or termination of the notice and waiting period under the HSR Act is
delayed because of lengthy government review, or if the Federal Trade Commission
or Department of Justice successfully challenges such a license, development and
commercialization could be delayed or precluded and our business could be
adversely affected.

WE HAVE LIMITED SALES AND MARKETING EXPERIENCE AND EXPECT TO INCUR SIGNIFICANT
EXPENSES IN DEVELOPING A SALES FORCE. WE ALSO RELY ON THIRD PARTIES FOR SALES OF
OUR PRODUCTS. IN ADDITION, OUR LIMITED SALES AND MARKETING EXPERIENCE MAY
RESTRICT OUR SUCCESS IN COMMERCIALIZING OUR PRODUCTS.

    We currently have limited marketing and sales experience. If we successfully
develop and obtain regulatory approval for the products we are currently
developing, we may license some of them to large pharmaceutical companies or
market and sell through our direct sales force or through other arrangements,
including co-promotion arrangements. We have established a direct sales force to
market XOPENEX. We also expect to use a direct sales force to market SOLTARA
brand tecastemizole, formerly known as norastemizole, if approved. As we begin
to enter into co-promotion arrangements or market and sell additional products
directly, we will need to significantly expand our sales force. Our limited
experience in developing, maintaining and expanding a direct sales force may
restrict our success in commercializing our products. We expect to incur
significant expense in expanding our direct sales force. With respect to
products under development, such as SOLTARA brand tecastemizole, we expect to
incur significant costs in developing a sales force before the product has been
approved for marketing.

                                       20
<Page>
    Our ability to realize significant revenues from direct marketing and sales
activities depends on our ability to attract and retain qualified sales
personnel in the pharmaceutical industry and competition for these persons is
intense. If we are unable to attract and retain qualified sales personnel, we
will not be able to successfully expand our marketing and direct sales force on
a timely or cost effective basis. We may also need to enter into additional
co-promotion arrangements with third parties where our own direct sales force is
neither well situated nor large enough to achieve maximum penetration in the
market. We may not be successful in entering into any co-promotion arrangements,
and the terms of any co-promotion arrangements may not be favorable to us. We
depend in large part on a third party sales organization for sales of XOPENEX
and we may contract with third party contract sales organizations in the future
for other products if successfully developed, including SOLTARA brand
tecastemizole. We cannot control the level of effort and quality of service
provided by co-promoters or any third party sales force. If the level of effort
and/or quality of service provided by these third parties is not adequate, our
revenues would be adversely affected.

IF WE DO NOT MAINTAIN CURRENT GOOD MANUFACTURING PRACTICES, THEN THE FDA COULD
REFUSE TO APPROVE MARKETING APPLICATIONS. WE DO NOT HAVE THE CAPABILITY TO
MANUFACTURE IN SUFFICIENT QUANTITIES ALL OF THE PRODUCTS WHICH MAY BE APPROVED
FOR SALE, AND DEVELOPING AND OBTAINING THIS CAPABILITY WILL BE TIME CONSUMING
AND EXPENSIVE.

    The FDA and other regulatory authorities require that our products be
manufactured according to their good manufacturing practices standards. The
failure by us, our collaborative development partners or third party
manufacturers to maintain current good manufacturing practices compliance and/or
our failure to scale up our manufacturing processes could lead to refusal by the
FDA to approve marketing applications. Failure in either respect could also be
the basis for action by the FDA to withdraw approvals previously granted and for
other regulatory action. We are entitled to receive royalties on sales, if any,
of desloratadine under the DCL Agreement with Schering. In February 2001,
Schering announced that it had been advised by the FDA that current good
manufacturing practices deficiencies cited by the FDA would need to be resolved
prior to FDA approval of desloratadine. We do not know if or when desloratadine
may be approved or the timing of commercialization of this compound.

    Failure to increase our manufacturing capabilities may mean that even if we
develop promising new products, we may not be able to produce them. We currently
operate a manufacturing plant that is compliant with current good manufacturing
practices that we believe can produce commercial quantities of XOPENEX and
support the production of our other possible products in amounts needed for our
clinical trials. However, we will not have the capability to manufacture in
sufficient quantities all of the products which may be approved for sale.
Accordingly, we will be required to spend money to expand our current
manufacturing facility, build an additional manufacturing facility or contract
the production of these drugs to third-party manufacturers.

OUR RELIANCE ON THIRD-PARTY MANUFACTURERS COULD ADVERSELY AFFECT OUR ABILITY TO
MEET OUR CUSTOMERS' DEMANDS.

    Automatic Liquid Packaging, a division of Cardinal Health, Inc., is
currently the sole finished goods manufacturer of our product XOPENEX. If
Automatic Liquid Packaging experiences delays or difficulties in producing,
packaging or delivering XOPENEX, or if they fail to comply with good
manufacturing practices regulations we could be unable to meet our customers'
demands for XOPENEX, which could lead to customer dissatisfaction and damage to
our reputation. Furthermore, if we are required to change manufacturers, we will
be required to verify that the new manufacturer maintains facilities and
procedures that comply with quality standards and with all applicable good
manufacturing practices regulations and guidelines. The delays associated with
the verification of a new manufacturer could negatively affect our ability to
produce XOPENEX in a timely manner or within budget.

                                       21
<Page>
    We currently have a supply contract with ChiRex Inc. that commits us to
purchase through December 31, 2001 all of our annual requirements of those drugs
that we will market directly through our sales force, provided ChiRex meets
certain pricing, supply and quality control conditions. If ChiRex experiences
delays or difficulties in producing, packaging or delivering the drugs, market
introduction and subsequent sales of the drugs that we market through our sales
force could be adversely affected. Under this supply agreement, however, we
retain the right to manufacture limited quantities of our drugs in our Nova
Scotia manufacturing plant.

IF WE OR OUR COLLABORATION PARTNERS FAIL TO OBTAIN AN ADEQUATE LEVEL OF
REIMBURSEMENT FOR OUR FUTURE PRODUCTS OR SERVICES BY THIRD PARTY PAYORS, THERE
MAY BE NO COMMERCIALLY VIABLE MARKETS FOR OUR PRODUCTS OR SERVICES.

    The availability and amounts of reimbursement by governmental and other
third party payors affects the market for any pharmaceutical product or service.
These third party payors continually attempt to contain or reduce the costs of
healthcare by challenging the prices charged for medical products and services.
In certain foreign countries, including the countries of the European Union, the
pricing of prescription pharmaceuticals is subject to governmental control. We
may not be able to sell our products profitably if reimbursement is unavailable
or limited in scope or amount.

    In both the United States and certain foreign jurisdictions, there have been
a number of legislative and regulatory proposals to change the healthcare
system. Further proposals are likely. The potential for adoption of these
proposals affects or will affect our ability to raise capital, obtain additional
collaboration partners and market our products. We expect to experience pricing
pressure for our existing products and any future products for which marketing
approval is obtained due to the trend toward managed healthcare, the increasing
influence of health maintenance organizations and additional legislative
proposals.

WE COULD BE EXPOSED TO SIGNIFICANT LIABILITY CLAIMS THAT COULD PREVENT OR
INTERFERE WITH OUR PRODUCT COMMERCIALIZATION EFFORTS.

    We may be subjected to product liability claims that arise through the
testing, manufacturing, marketing and sale of human health care products. These
claims could expose us to significant liabilities that could prevent or
interfere with our product commercialization efforts. Product liability claims
could require us to spend significant time and money in litigation or to pay
significant damages. Although we maintain product liability insurance coverage
for both the clinical trials and commercialization of our products, it is
possible that we will not be able to obtain further product liability insurance
on acceptable terms, if at all, and that our insurance coverage may not provide
adequate coverage against all potential claims.

IF SUFFICIENT FUNDS TO FINANCE OUR BUSINESS ARE NOT AVAILABLE TO US WHEN NEEDED
OR ON ACCEPTABLE TERMS, THEN WE MAY BE REQUIRED TO DELAY, SCALE BACK, ELIMINATE
OR ALTER OUR STRATEGY FOR OUR PROGRAMS.

    We may require additional funds for our research and product development
programs, operating expenses, the pursuit of regulatory approvals, license or
acquisition opportunities and the expansion of our production, sales and
marketing capabilities. Historically, we have satisfied our funding needs
through collaboration arrangements with corporate partners and equity and debt
financings. These funding sources may not be available to us when needed in the
future, and, if available, they may not be on terms acceptable to us.
Insufficient funds could require us to delay, scale back or eliminate certain of
our research and product development programs or to license third parties to
commercialize products or technologies that we would otherwise develop or
commercialize ourselves. Our cash requirements may vary materially from those
now planned because of factors including:

    - increased research and development expenses;

                                       22
<Page>
    - patent developments;

    - licensing or acquisition opportunities;

    - relationships with collaboration partners;

    - the FDA regulatory process;

    - our capital requirements; and

    - selling, marketing and manufacturing expenses in connection with
      commercialization of products.

WE EXPECT TO FACE INTENSE COMPETITION AND OUR COMPETITORS HAVE GREATER RESOURCES
AND CAPABILITIES THAN WE HAVE.

    Developments by others may render our products or technologies obsolete or
noncompetitive. We expect to encounter intense competition in the sale of our
current and future products. If we are unable to compete effectively, our
financial condition and results of operations could be materially adversely
affected because we may use our financial resources to seek to differentiate
ourselves from our competition and because we may not achieve our product
revenue objectives. Many of our competitors and potential competitors, which
include pharmaceutical companies, biotechnology firms, universities and other
research institutions, have substantially greater resources, manufacturing and
marketing capabilities, research and development staff and production facilities
than we have. The fields in which we compete are subject to rapid and
substantial technological change. Our competitors may be able to respond more
quickly to new or emerging technologies or to devote greater resources to the
development, manufacture and marketing of new products and/or technologies than
we can. As a result, any products and/or technologies that we develop may become
obsolete or noncompetitive before we can recover expenses incurred in connection
with their development.

FLUCTUATIONS IN THE DEMAND FOR PRODUCTS, THE TIMING OF COLLABORATION
ARRANGEMENTS AND REGULATORY APPROVAL, ANY TERMINATION OF DEVELOPMENT EFFORTS,
EXPENSES AND THE RESULTS OF OPERATIONS OF OUR SUBSIDIARIES WILL CAUSE
FLUCTUATIONS IN OUR QUARTERLY OPERATING RESULTS, WHICH COULD CAUSE VOLATILITY IN
OUR STOCK PRICE.

    Our quarterly operating results are likely to fluctuate significantly, which
could cause our stock price to be volatile. These fluctuations will depend on
factors which include:

    - the success and timing of regulatory filings and approvals for products
      developed by us or our collaboration partners or for collaborative
      agreements;

    - the timing of collaboration agreements for development of our
      pharmaceutical candidates and development costs for those pharmaceuticals;

    - the termination of development efforts of any product under development or
      any collaboration agreement;

    - the timing of receipt of up front, milestone or royalty payments under
      collaboration agreements;

    - the timing of product sales and market penetration;

    - the timing of operating expenses, including selling and marketing expenses
      and the costs of expanding and maintaining a direct sales force; and

    - the timing of expenses we may incur with respect to any license or
      acquisitions of products or technologies.

                                       23
<Page>
OUR STOCK PRICE COULD BE HIGHLY VOLATILE, WHICH COULD CAUSE YOU TO LOSE PART OR
ALL OF YOUR INVESTMENT.

    The market price of our common stock, like that of the common stock of many
other pharmaceutical and biotechnology companies, may be highly volatile. In
addition, the stock market has experienced extreme price and volume
fluctuations. This volatility has significantly affected the market prices of
securities of many pharmaceutical and biotechnology companies for reasons
frequently unrelated to or disproportionate to the operating performance of the
specific companies. These broad market fluctuations may adversely affect the
market price of our common stock. Prices for our common stock will be determined
in the marketplace and may be influenced by many factors, including variations
in our financial results and investors' perceptions of us, changes in
recommendations by securities analysts as well as their perceptions of general
economic, industry and market conditions.

                                       24
<Page>
                                    ITEM 3.
           QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK

MARKET RISK

    The Company is exposed to market risk from changes in interest rates and
equity prices, which could affect its future results of operations and financial
condition. These risks are described in the Company's Annual Report on Form 10-K
for the year ended December 31, 2000. As of November 7, 2001, there have been no
material changes to the market risks described in the Company's Annual Report on
Form 10-K for the year ended December 31, 2000. Additionally, the Company does
not anticipate any near-term changes in the nature of its market risk exposures
or in management's objectives and strategies with respect to managing such
exposures.

                                    PART II
                               OTHER INFORMATION

ITEM 1. LEGAL PROCEEDINGS

    Currently, Sepracor is not a party to any material legal proceedings.

ITEMS 2-6. NONE

                                       25
<Page>
                                   SIGNATURES

    Pursuant to the requirements of the Securities Exchange Act of 1934, the
registrant has duly caused this report to be signed on its behalf by the
undersigned thereunto duly authorized.

<Table>
<S>                                                    <C>  <C>
                                                       SEPRACOR INC.

Date: November 7, 2001                                 By:           /s/ TIMOTHY J. BARBERICH
                                                            -----------------------------------------
                                                                       Timothy J. Barberich
                                                               CHAIRMAN AND CHIEF EXECUTIVE OFFICER
                                                                  (PRINCIPAL EXECUTIVE OFFICER)

Date: November 7, 2001                                 By:            /s/ ROBERT F. SCUMACI
                                                            -----------------------------------------
                                                                        Robert F. Scumaci
                                                              EXECUTIVE VICE PRESIDENT, FINANCE AND
                                                                  ADMINISTRATION, AND TREASURER
                                                                  (PRINCIPAL ACCOUNTING OFFICER)
</Table>

                                       26
<Page>
                                   SIGNATURES

    Pursuant to the requirements of the Securities Exchange Act of 1934, the
registrant has duly caused this report to be signed on its behalf by the
undersigned thereunto duly authorized.

<Table>
<S>                                                    <C>  <C>
                                                       SEPRACOR INC.

Date: November 13, 2001                                By:            /s/ ROBERT F. SCUMACI
                                                            -----------------------------------------
                                                                        Robert F. Scumaci
                                                              EXECUTIVE VICE PRESIDENT, FINANCE AND
                                                                  ADMINISTRATION, AND TREASURER
                                                                  (PRINCIPAL ACCOUNTING OFFICER)
</Table>

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