Danbury, CT, June 2, 2003 -- Penwest Pharmaceuticals Co. (Nasdaq: PPCO) announced today that Endo Pharmaceuticals, Penwest's partner in the development and commercialization of oxymorphone ER, reported positive results for that drug from a study in cancer pain. The Phase III clinical trial, presented today at the 2003 Annual Meeting of the American Society of Clinical Oncology (ASCO), compared the analgesic efficacy and tolerability of two opioids in patients with moderate- to-severe cancer pain in a double-blind, two-way crossover design. Endo reported that in this study, oxymorphone ER provided pain relief for patients with moderate-to-severe cancer pain equivalent to oxycodone controlled release (CR) at half the milligram dose.

Controlling cancer pain is a major part of the overall treatment of cancer. According to the American Cancer Society (ACS), people who have been diagnosed with cancer fear the pain associated with the disease more than any other symptom. Significant pain can be a lifestyle-limiting problem for cancer patients, and fewer than 50 percent of those with advanced disease receive adequate pain treatment. Physicians often prescribe opioids, the strongest pain relievers available, to cancer pain patients, and use a common strategy called opioid rotation to overcome unmanageable side effects or inadequate analgesia as part of a patient's cancer pain treatment regimen.

Study Results as presented by Endo
Data were presented from a Phase III, randomized, double-blind, two-way crossover study of 44 cancer patients who required opioid analgesics for treatment of moderate-to-severe cancer pain. Study participants were initially stabilized on oxycodone CR during a seven-to-10-day titration/stabilization phase. They were subsequently randomized to seven to 10 days of double-blind treatment of either oxycodone CR or oxymorphone ER with an estimated potency conversion of 2:1, respectively. Dosages remained fixed from days 4 to 7, and morphine-sulfate immediate release 15 mg tablets were allowed as a rescue medication. Patients then crossed over to the alternate therapy for seven to 10 days.

Efficacy was assessed by pain intensity and relief using the Brief Pain Inventory (BPI), global evaluations and Karnofsky performance status. The primary efficacy endpoint was average pain intensity as measured by BPI during the preceding 24 hours. Results indicated that the average daily pain intensity ratings of oxymorphone ER and oxycodone CR were comparable. In addition, adequate analgesia was maintained in both oxymorphone ER and oxycodone CR groups during the double-blind treatment period. The mean daily dose of oxycodone CR was 91.9 versus 45.9 mg of oxymorphone ER, confirming an equianalgesic dose ratio of 2:1, respectively. The average daily dose of rescue medication was low in both groups, at about 15 mg per day of morphine sulfate immediate release.

Side effects were similar between both active treatment groups and were of the type and severity of those routinely seen with other opioids, including constipation, sedation, nausea, pruritus (itching), sweating, dizziness, and vomiting. The majority of adverse events were of mild or moderate severity.

Oxymorphone ER is currently under review by the U.S. Food and Drug Administration (FDA). The safety and efficacy of oxymorphone ER have not been established by the FDA.

Endo developed oxymorphone ER using Penwest Pharmaceuticals' proprietary time-release technology, TIMERx(R). The two companies provided joint funding for this study.

About Cancer Pain
An estimated eight million people in the U.S. have had cancer at some time in their lives, and roughly one million new persons will be added to their ranks every year. If the disease progresses to advanced stages, nearly 70 percent of patients will have significant pain. The American Cancer Society takes the position that pain is best controlled through early, aggressive treatment with strong medications, which often include opioids. It is almost always possible to relieve the pain caused by cancer, and this goal of treatment is viewed as a cornerstone of modern cancer management.

About Penwest
Penwest is a drug delivery company utilizing proprietary technologies to develop drugs internally and with third party collaborators. Penwest's pharmaceutical portfolio includes four marketed products utilizing its proprietary controlled release drug delivery technology, TIMERx(R), which were developed with collaborators such as Mylan Pharmaceuticals, Sanofi, Merck S.A. and Schering OY, and which have been approved in various countries. In addition, the Company has several products in its pipeline that are in various stages of development, including the pain product oxymorphone ER, which is currently under review at the FDA.

The matters discussed herein contain forward-looking statements that involve risks and uncertainties, which may cause Penwest's actual results in future periods to be materially different from any future performance suggested herein. For this purpose, any statements contained herein that are not statements of historical fact may be deemed to be forward-looking statements. Without limiting the foregoing, the words, "believes," "anticipates," "plans," "expects," "intends," "potential," and similar expressions are intended to identify forward-looking statements. Important factors that could cause results to differ materially include the Company's dependence on its drug delivery business without the revenues and cash flows of the excipient business; dependence on collaborators to, among other things, sell products for which the Company receives royalties, file for regulatory approvals, and advance clinical development and commercialization of products; the ability to enter into additional collaborations; uncertainty of success of collaborations; the risk of patent litigation; regulatory risks relating to TIMERx(R) drugs in development; the timing of clinical trials; actual and potential competition; the timing and outcome of regulatory approval of products, including oxymorphone ER; the need for capital; and other risks as set forth under the caption Certain Factors That May Affect Future Results in Penwest's Annual Report on Form 10-Q filed with the Securities and Exchange Commission on May 14, 2003, which risk factors are incorporated herein by reference. Penwest disclaims any intention or obligation to update any forward-looking statements.