Sepracor Announces Commencement of Phase I Clinical Study for SEP-225289 for Major Depression.

MARLBOROUGH, Mass. -- Sepracor Inc. (Nasdaq: SEPR) today announced that it has initiated a Phase I, single-blind, randomized, placebo-controlled safety, tolerability and pharmacokinetic study for SEP-225289 for the treatment of Major Depressive Disorder (MDD).

Based on preclinical study data, Sepracor believes that SEP-225289 has the potential to be a leading drug candidate in the newly emerging field of triple reuptake inhibitors (TUIs). SEP-225289 has been shown in preclinical studies to be a potent and balanced reuptake inhibitor of serotonin, norepinephrine and dopamine (SNDRI). Serotonin, norepinephrine and dopamine are neurotransmitters associated with depression. There are currently no marketed treatments for depression that inhibit reuptake of all three neurotransmitters. Studies suggest that a triple mechanism of action may provide a broader spectrum of therapy than currently marketed antidepressants.

"We believe that a triple reuptake inhibitor may exhibit greater efficacy and faster onset of action than currently marketed antidepressants," said Mark H.N. Corrigan, M.D., Executive Vice President, Research and Development at Sepracor. "This novel combination of properties in a single compound, if verified in our planned clinical research program, may provide a breakthrough in the treatment for depression and could have the potential to address a number of related maladies including substance abuse and other central nervous system conditions."

According to the National Institutes of Health, major depression is one of the most common chronic conditions. In any given year, it is estimated that approximately 18 million Americans have a depressive disorder. Major depression is described as when five or more symptoms of depression are present for at least two weeks. These symptoms include feeling sad, hopeless, worthless, or pessimistic. In addition, people with major depression often have behavior changes, such as new eating and sleeping patterns. Evidence suggests that between 29 percent and 46 percent of depressed patients fail to fully respond to antidepressant treatment with marketed drugs.(1) According to IMS Health information, the U.S. market for prescription antidepressants was approximately $10.9 billion in 2004.

About Sepracor

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 compound candidates with a focus on respiratory and central nervous system disorders. The company's commercialization efforts are carried out by its U.S.-based, 1,250-person, primary care and specialty-oriented sales force. Sepracor's corporate headquarters are located in Marlborough, Massachusetts.

This news release contains forward-looking statements that involve risks and uncertainties, including statements with respect to the safety, efficacy, potential benefits and successful development and regulatory approval SEP-225289 and the company's other pharmaceuticals under development. Among the factors that could cause actual results to differ materially from those indicated by such forward-looking statements are: the results of clinical trials with respect to SEP-225289; the timing and success of submission, acceptance, and approval of regulatory filings for SEP-225289; the scope of Sepracor's patents and the patents of others; the ability of the company to attract and retain qualified personnel; the availability of sufficient funds to continue research and development efforts; the continued ability of Sepracor to meet its debt obligations when due; and certain other factors that may affect future operating results and are detailed in the company's quarterly report on Form 10-Q for the quarter ended June 30, 2005 filed with the Securities and Exchange Commission.

In addition, the statements in this press release represent Sepracor's expectations and beliefs as of the date of this press release. Sepracor anticipates that subsequent events and developments may cause these expectations and beliefs to change. However, while Sepracor may elect to update these forward-looking statements at some point in the future, it specifically disclaims any obligation to do so. These forward-looking statements should not be relied upon as representing Sepracor's expectations or beliefs as of any date subsequent to the date of this press release.

(1) Fava M, Davidson KG. Definition and epidemiology of treatment-resistant depression. Psychiatr Clin North Am 1996; 19:179-200

For a copy of this release or any recent release, visit www.sepracor.com.