A randomized, 4-week, double-blind trial followed by an open-label extension trial assessed the efficacy and safety of a once-daily, extended-release morphine formulation (Avinza (previously referred to as Morphelan)) in 295 patients with chronic, moderate-to-severe osteoarthritis pain who had failed to obtain adequate pain relief with NSAIDs and acetaminophen. Participants received one of four treatments: Avinza 30 mg once daily (QAM or QPM), MS Contin(R) 15 mg twice daily, or placebo twice daily. Patients (n =181) received Avinza QAM or QPM during the 26-week open-label extension trial and could increase their dose to optimize pain control. Avinza and MS Contin reduced pain and improved several sleep measures versus placebo. Analgesic efficacy was comparable between Avinza and MS Contin; however, Avinza QAM demonstrated greater improvements in overall quality of sleep. The most common adverse events were constipation and nausea. The majority of AEs occurred at a similar incidence among the active treatment groups.