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What Vivitrol is
A monthly naltrexone injection.
Vivitrol is the brand name for extended-release injectable naltrexone — an intramuscular injection administered once monthly by a clinician. It contains naltrexone microspheres suspended in a biodegradable polymer that releases medication over 30 days.
Naltrexone is an opioid antagonist — it completely blocks opioid receptors. Patients on Vivitrol generally have opioid receptor blockade during the injection's active period, which reduces or prevents the effects of opioids. Unlike buprenorphine and methadone, naltrexone is not itself an opioid and has no abuse potential.
Requirements and considerations
Vivitrol requires complete opioid detoxification first.
The most significant clinical constraint on Vivitrol is that patients generally need to be fully opioid-free before the first injection, often for about 7–10 days depending on the opioid involved and the clinical situation. If naltrexone is administered while opioids are still present, it will precipitate acute withdrawal, which can be severe.
This detoxification requirement is a real barrier in practice. The required opioid-free period can make initiation difficult, and some patients do not successfully complete that transition.
Reladetoxification window is clinically important because opioid tolerance decreases during this period, which can increase overdose risk if relapse occurs. The period between stopping opioids and receiving the first Vivitrol injection represents a window of high relapse risk and reduced opioid tolerance — making overdose particularly dangerous if relapse occurs.
Comparison with buprenorphine
Different medications for different clinical situations.
Initiation
Buprenorphine can be started while a patient is still opioid-dependent — no detoxification required. Vivitrol requires complete opioid-free status.
Mechanism
Buprenorphine is a partial agonist — it reduces withdrawal and cravings by partially activating receptors. Vivitrol is a pure antagonist — it blocks receptors entirely and does not address withdrawal or craving in the same way.
Evidence
Both are FDA-approved and evidence-based. A large NIDA-funded trial (X:BOT, 2018) found comparable outcomes between extended-release naltrexone and buprenorphine/naloxone for those who successfully initiated treatment — but significantly lower initiation rates for naltrexone due to the detoxification barrier.
Who may benefit
Vivitrol may be appropriate for patients who have completed detoxification and prefer an opioid antagonist approach, or for patients in settings where opioid-based medication is unavailable or declined — such as certain criminal justice or professional licensing contexts.
Sources
Where this information comes from.
Lee et al. — X:BOT Trial (2018)
NEJM. Extended-release naltrexone vs. buprenorphine/naloxone — comparable outcomes among those who initiated, but lower initiation rates with naltrexone.
Vivitrol Prescribing Information
Official FDA prescribing information for extended-release injectable naltrexone.
ASAM National Practice Guideline (2020)
Clinical guidance on naltrexone including patient selection, initiation, and management.