"VIVITROL was approved in 2006 by the FDA as an extended-release formulation of naltrexone for the treatment of alcohol dependence in patients who are able to abstain from alcohol in an outpatient setting prior to initiation of treatment. VIVITROL is administered by intramuscular (IM) injection once per month."

Source

"VIVITROL® (naltrexone for extended-release injectable suspension)," FDA Psychopharmacologic Drugs Advisory Committee Meeting (Waltham, MAP: Alkermes, Inc., September 16, 2010), p. 10.