Naltrexone is the third FDA-approved medication for opioid use disorder — and the one that works on a fundamentally different principle than the other two: it blocks opioid effects entirely rather than managing them.
How it works
Naltrexone is an opioid antagonist — it binds to opioid receptors without activating them, blocking other opioids from having an effect. Unlike buprenorphine (a partial agonist) or methadone (a full agonist), naltrexone doesn’t suppress withdrawal or cravings through receptor activation; instead, if someone uses an opioid while on naltrexone, it simply won’t produce the usual effect.
Forms it comes in
- Vivitrol: a monthly injection, the most commonly used form for opioid use disorder
- Oral tablets: taken daily, though less commonly used for opioid use disorder specifically due to adherence challenges — missing a dose removes the blocking effect
The single biggest practical challenge
Unlike buprenorphine and methadone, which can be started while someone is still in withdrawal, naltrexone requires being fully opioid-free for roughly 7–10 days first — starting too early causes severe precipitated withdrawal. [full article on this specific challenge] This waiting period is, for many people, the hardest part of choosing this medication.
Why someone might choose naltrexone
- No physical opioid dependence on the medication itself, which matters to some people psychologically, even though physical dependence and addiction aren’t the same thing [link to that distinction article]
- No diversion or misuse potential, since it has no opioid effect itself
- Monthly injection removes daily dosing decisions entirely once started
- Some employment or legal contexts (certain professions, some drug court programs) show a preference for naltrexone specifically, given its non-agonist profile
Real limitations to know about
- The 7–10 day opioid-free requirement is a genuine barrier — this is not a minor inconvenience
- If naltrexone is stopped or a dose is missed, opioid tolerance can return, meaning a return to previous opioid use afterward carries real overdose risk [link to overdose risk after a break tool]
- It doesn’t address cravings through the same brain mechanism buprenorphine and methadone do — some people find this makes cravings harder to manage, though evidence on comparative craving control is mixed
- Cost without insurance is notably high — roughly $1,000–1,300/month for the injection [link to cost estimator tool]
Getting started
See our article on navigating the required opioid-free window [link] before starting, and our full three-way comparison [link] to see how this stacks up against buprenorphine and methadone for your specific situation.
Medically reviewed by [pending]. Sources: FDA prescribing information for naltrexone and Vivitrol, SAMHSA TIP 63.