Naltrexone: What it does, how it works, and what to expect
Naltrexone blocks opioid receptors to reduce cravings and dependence. Here's how it works, what conditions it treats, and what side effects to watch for.
What is naltrexone?
Naltrexone is an opioid antagonist: it blocks opioid receptors in the brain. This means it stops opioids from working if you take them, and it reduces cravings that drive addiction.
What it treats
Naltrexone is used for two main conditions:
- Opioid use disorder (heroin, prescription painkillers, and synthetic opioids)
- Alcohol use disorder
For opioid use disorder, it comes as a daily pill or as Vivitrol, a monthly injection. For alcohol use disorder, it's typically a daily pill.
How it works
Naltrexone attaches to opioid receptors without triggering them. This blocks the reward pathway that makes opioid and alcohol use feel good. The result: fewer cravings and less reinforcement if you slip.
It does not treat withdrawal symptoms. If you're physically dependent on opioids, you'll need medical detoxification or a transition medication like buprenorphine before starting naltrexone.
Side effects
Common side effects include:
- Nausea and vomiting
- Headache
- Fatigue
- Muscle aches
- Insomnia
Side effects are usually mild and fade after the first few weeks.
Important notes
Naltrexone works best paired with counselling and behavioural support. Tell your doctor about all opioid use, including prescription painkillers, before starting; naltrexone can trigger sudden withdrawal if opioids are in your system. Do not take naltrexone if you're pregnant or breastfeeding without explicit medical guidance.