The purpose of this study is to determine the safety and effectiveness of 650 mg and 1300 mg acetaminophen extended release given three times a day for the relief of signs and symptoms of osteoarthritis of the hip or knee for a period of 12 weeks.

This is a randomized, double-blind, placebo-controlled study to determine the safety and effectiveness of 650 mg and 1300 mg acetaminophen extended release given three times a day as compared with placebo, for the relief of signs and symptoms of osteoarthritis of the hip or knee for a period of 12 weeks. Propoxyphene Hydrochloride capsules 65 mg are used as rescue medication if subjects experience inadequate pain relief. The primary efficacy assessments are the average change from baseline to the final on-therapy visit for the WOMAN pain subscale score and the WOMAC physical function subscale scare, and the subject's average global assessment of their response to therapy through the final on-therapy visit. Safety assessments at study visits consist of monitoring adverse events, vital signs, study joint assessments and clinical laboratory determinations. The hypothesis is that 1950 mg per day and/or 3900 mg per day acetaminophen extended release are superior to placebo for the relief of the signs and symptoms of osteoarthritis of the hip or knee with respect to all three primary efficacy endpoints. Treatment consisted of either one 650 mg acetaminophen extended release caplet plus one placebo caplet (acetaminophen 1950 mg group); two 650 mg acetaminophen extended release caplets (acetaminophen 3900 mg group); or two placebo caplets administered orally every eight hours for 12 weeks.

Inclusion Criteria:

• Symptomats of osteoarthritis of the hip or knee for a minimum of six months
• History of hip or knee pain due to osteoarthritis requiring the use of NSAIDs, acetaminophen, or another analgesic agent on a regular basis (>= three days per week) for at least three months before the screening visit
• History of positive therapeutic benefit with acetaminophen use for osteoarthritis pain
• History of osteoarthritis pain (moderate, moderately severe, or severe) of the hip or knee when not taking osteoarthritis analgesic medication
• Must have a pain level of moderate or moderately severe for 24 hours over the previous 24 hours prior to the baseline visit, and at baseline, demonstrate a 20% or greater increase in the pain subscale score, relative to the score at screening

Exclusion Criteria:

• History of surgery, including arthroscopy, or major trauma to the study joint in the previous six months before the screening visit
• Grade 1 or grade 4 severity of the study joint based on the Kellgren and Lawrence radiographic criteria
• Maximum osteoarthritis pain intensity of none, mild or severe experienced over the previous 24 hours of the baseline visit
• Signs of clinically important active inflammation of the study knee joint including redness, warmth and/or a large, bulging effusion with the loss of normal contour at the screening and/or baseline visits