Participants eligible for this extension study had received all 6 injections of study drug in the base study; those who received Medisorb naltrexone in the base study who also received all 13 injections in this extension therefore had a duration of exposure of approximately 76 weeks (~1.5 years) upon completion of this extension. For participants who had received placebo in the base study, maximum duration of exposure was approx. 48 weeks (1 year).