The primary purpose of this study is to determine the efficacy and safety of three dose levels of cobiprostone as compared to placebo in OA/RA patients treated with an NSAID for 20 months.

Inclusion Criteria:

• Patient is more than 40 and less than 70 years of age.
• Patient has confirmed osteoarthritis (OA) and/or rheumatoid arthritis (RA) and could benefit from NSAID therapy.
• No current gastrointestinal H. pylori infection.

Exclusion Criteria:

• Known allergy or hypersensitivity to NSAIDs, or has any other contraindicated condition(s) to NSAID therapy.
• Patient has undergone a gastrointestinal or abdominal surgical procedure within 90 days prior to the Screening Visit, or has had a bowel resection at any time.
• Medical history includes prior or active GI complications and/or disorders, including but not limited to Barrett's esophagus, erosive esophagitis, esophageal stricture or ring, gastric obstruction, irritable bowel syndrome (IBS), or inflammatory bowel disease (IBD).
• Active symptomatic peptic ulcer disease or GI bleeding.
• Patient has received cobiprostone (SPI-8811; RU-8811) or AMITIZA (other names: lubiprostone, SPI-0211, or RU-0211) at any time prior to participation in this study.