Vivitrol (naltrexone) starts to work on the first day it is injected, and its effects last for a month. The first peak of the drug in your blood occurs at about 2 hours after injection. Then the drug is slowly released over the remaining month.

Vivitrol injection is specially formulated so that the naltrexone is contained in small spheres of a polymer substance. These spheres are suspended in the liquid that is injected. The spheres release the naltrexone into the blood in phases.

Because Vivitrol starts to work right away, it is very important that you do not have alcohol or opioids in your system at the time the medication is started. You should be opioid-free for at least 7 to 14 days (depending on which opioid you've been using) or have completed alcohol detoxification before taking Vivitrol. If you are not opioid- and alcohol-free, Vivitrol can result in serious withdrawal symptoms that might require hospitalization.

Vivitrol is an intramuscular shot that is given monthly in the buttocks to help people with opioid or alcohol dependence control cravings and avoid relapse. The monthly dose for both uses is 380 mg. Vivitrol works best when it is part of a comprehensive treatment plan that includes a counseling program.

Vivitrol is a brand name for the drug naltrexone. Naltrexone is an opioid antagonist, which means it binds to your body's opiate receptors without providing any of the usual effects of opioids. Opioids, such as prescription pain medication or illegal drugs like heroin, can cause a feeling of pleasure or euphoria (a high), and they have the potential to be abused. Naltrexone, by binding to and blocking opiate receptors, prevents the high and pleasure feelings from opioids from occurring, as well as any therapeutic effects, such as pain management.

Exactly how naltrexone works for alcohol use disorder is not completely understood. It may work by binding endorphin receptors in the brain. It somehow blunts the desire to drink and lowers the feeling of intoxication, but you will still have a lack of judgment and coordination if alcohol is consumed while taking Vivitrol. Because it blocks some of the effects and feelings associated with drinking alcohol, it helps to reduce cravings and decrease alcohol consumption.