Cubist Pharmaceuticals, Inc. (NASDAQ: CBST) today announced the initiation of Phase 3 efficacy studies of bevenopran (previously known as CB-5945) in patients with chronic non-cancer pain and opioid-induced constipation (OIC). The Phase 3 program, ASCENT, includes three identically-designed studies that will enroll approximately 600 patients each (1,800 total) designed to evaluate the efficacy and safety of bevenopran (0.25 mg orally twice daily) vs. placebo. The ASCENT program also includes a 1,400-patient one-year, placebo-controlled safety study which was initiated in October 2012. “Effective management of OIC is extremely important for the millions of patients who need opioids to manage chronic non-cancer pain and there are limited treatment options currently available,” said Steven Gilman, Ph.D., Executive Vice President of Research and Development and Chief Scientific Officer of Cubist Pharmaceuticals. “We believe bevenopran has the potential to be an important option for managing constipation and related symptoms in patients taking chronic opioids for pain management.” The primary endpoint of the studies is the proportion of spontaneous bowel movement (SBM) responders over a 12-week treatment period. The Phase 3 efficacy trials also include, as a secondary endpoint, a patient reported outcome (PRO) measurement tool that was developed and validated using data from the Phase 2 studies of bevenopran. This measure, known as Chronic Opioid-Related Gastrointestinal Symptoms Scale (CORGISS), assesses GI symptoms associated with chronic opioid therapy. About Opioid-Induced Constipation (OIC) and bevenopran The American Pain Foundation estimates that nine percent of the U.S. adult population suffers from moderate to severe non-cancer related chronic pain, which is commonly defined as pain that lasts longer than the usual course of an injury or illness. Long-term management of chronic pain often includes treatment with opioid analgesics. Many people receiving this treatment will develop constipation, as well as other associated gastrointestinal complications. This is believed to be the result of the stimulation of mu opioid receptors in the gastrointestinal tract by opioid analgesics. The stimulation of these peripheral mu opioid receptors disrupts regulation of motility, secretion and absorption. Bevenopran is a peripherally acting mu opioid receptor antagonist drug candidate that is intended to block the adverse effects of opioid analgesics on the gastrointestinal tract without compromising the pain relief caused by opioid action in the central nervous system. About Cubist Cubist Pharmaceuticals, Inc. is a biopharmaceutical company focused on the research, development and commercialization of pharmaceutical products that address significant unmet medical needs in the acute care environment. Cubist is headquartered in Lexington, Mass. Additional information can be found on Cubist’s website at www.cubist.com. Cubist Safe Harbor Statement This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995 and other federal securities laws. Any statements contained herein which do not describe historical facts, including but not limited to, statements regarding the clinical development of bevenopran and the therapeutic potential of bevenopran for OIC and related symptoms, are forward-looking statements which involve risks and uncertainties that could cause actual results to differ materially from those discussed in such forward-looking statements. Such risks and uncertainties include, among others: the fact that drug development involves a high degree of risk and a high rate of failure and success in pre-clinical or early stage clinical trials does not mean that later stage trials will be successful; bevenopran may not show sufficient therapeutic effect or have an acceptable safety profile in Phase 3 clinical trials to obtain FDA approval (for example, if the clinical data shows an adverse cardiovascular safety signal); clinical trials of bevenopran may not be conducted in a timely manner and are dependent on our ability to successfully work with, and the performance of, our third party clinical research organizations that we significantly rely on to help us conduct clinical trials; the timing and feasibility of any subsequent trials is dependent on our ability to successfully work with regulatory authorities, including the FDA on the design of the trials, among other things; acceptance, review and approval decisions for new drug applications by regulatory authorities is an uncertain and evolving process and regulatory authorities retain significant discretion at all stages of the review and approval process; if approved, the commercial market for bevenopran may not be as large as we anticipate, including as a result of bevenopran competing with products currently in development which may have superior efficacy, safety or product profiles as bevenopran; technical difficulties or excessive costs relating to the manufacture or supply of bevenopran, including our dependence on and the performance of our third party contract manufacturers that manufacture and supply bevenopran on our behalf; we may not be able to maintain and enforce the intellectual property protecting bevenopran; and those additional factors discussed in our most recent quarterly report on Form 10-Q filed with the Securities and Exchange Commission. We caution investors not to place considerable reliance on the forward-looking statements contained in this press release. These forward-looking statements speak only as of the date of this document, and we undertake no obligation to update or revise any of these statements.