We think that retention and outcome can be improved by using a longer acting naltrexone preparation, and in this study we propose to compare ON with a depot naltrexone implant (DNI) that is manufactured and approved for use in Russia, and provides opioid blockade for 8-10 weeks. We will use a placebo-controlled, double-blind/double-dummy design since a placebo-controlled trial is required by the Russian equivalent of our FDA as a condition for testing a pharmacotherapy. Participants will be male and female heroin addicts who have been detoxified in addiction treatment hospitals or outpatient settings in St. Petersburg and have a family member willing and able to supervise medication adherence and facilitate follow-up. After giving informed consent and confirming the absence of physiologic dependence, 300 patients will be randomly assigned to a 6-month treatment in one of three groups of 100 each: oral naltrexone (ON) + depot naltrexone implant placebo (DNIP); oral naltrexone placebo (ONP) + depot naltrexone implant (DNI); or ONP + DNIP. All patients will receive biweekly clinical management/adherence enhancement counseling. Assessments will be done at baseline, at each biweekly appointment during the 6-months of medication treatment, and at 3 and 6 months following the end of study medication. Primary outcome will be the relapse free proportion at months 1-6; secondary outcomes will be time to dropout, opioid positive urines, HIV risk, use of alcohol and other drugs, psychiatric symptoms, and other measures of overall adjustment. We hypothesize that outcomes will be better with DNI than ON, and that each will be more effective than placebo.