Vivitrol: An extended release, injectable form of the medication Naltrexone, used to prevent opiate relapse after a person has safely detoxed from heroin or other opiates. Often intended for abating opiate cravings, Vivitrol blocks the effects of opioids, including pain relief or euphoric feelings. It is sometimes used to treat alcohol dependence and usually administered after a person has been on a regimen of the oral opiate withdrawal medication, Suboxone.