Naltrexone Extended-Release injectable Suspension 380 mg Vivitrol (RX)Vivitrol Naltrexone Extended Release Injectable Suspension 380mg is a medication used to help prevent relapse in those who have recently stopped using opioids or alcohol. It is a once monthly injection that contains naltrexone, which works by blocking the effects of opioids and alcohol in the brain. This can help reduce cravings and prevent a relapse from occurring. Vivitrol is intended to be used in combination with counseling or other support