• Vivitrol injection is a once-a-month extended release injection
• How long Vivitrol lasts depends on how fast your body breaks down the slow release formula and varies from person to person
• After the IM (intramusclar) injection most of the Vivitrol would have left the body 25 to 50 days
• For most people the effect from Vivitrol lasts for about a month in their body, so they need to have a new Vivitrol injection every 4 weeks or once a month, for it to keep having its effect.

When calculating how long Vivitrol lasts in the body, you need to consider its elimination half-life This is the time it takes for half of the drug to be metabolized and eliminated in the body. This varies from person to person with people ranging from being slower or faster at eliminating Vivitrol.

• The elimination half-life of Vivitrol injection is 5 to 10 days
• Generally, it takes approximately five half-lives for a drug to be eliminated from the body
• Faster elimination 5 X 5 days = 25 days
• Slower elimination 10 X 5 days = 50 days
• Vivitrol injection lasts in the body for a range of 25 to 50 days.

Vivitrol contains the active ingredient naltrexone which is used to reduce opiate dependence and alcohol dependence.