Naltrexone: what it treats, how to take it, side effects
Last updated September 3, 2026.
Naltrexone is an opiate antagonist - it decreases the craving for alcohol and blocks the effects of opioid medications and opioid street drugs. It is one leg of a three-legged stool: medication, counseling, and social support. It helps people who have already stopped stay stopped.
What does it treat?
Alcohol and opioid dependence - specifically, maintaining abstinence in people who have already stopped drinking or using. It is not for people still drinking heavily or still using, and it is not a withdrawal treatment: it does not prevent or relieve withdrawal symptoms, and it can cause or worsen them if opioids are still in your system.
How do you take it?
A tablet once a day at home with or without food, or on a supervised schedule at a clinic - daily, every other day, every third day, as the program prescribes. It only helps as long as you take it, so continue even when you feel strong. And the medication is only one leg: attend every counseling session, support meeting, and program your doctor recommends. Missed dose: take it when you remember unless the next one is close; never double up.
Side effects to know
- Common: nausea, vomiting, stomach pain or cramping, diarrhea, constipation, appetite loss, headache, dizziness, anxiety, nervousness, irritability, tearfulness, sleep trouble, energy changes, drowsiness, muscle or joint pain, and rash.
- Serious - call your doctor immediately: confusion, hallucinations, blurred vision, and severe vomiting or diarrhea.
Who should not take it?
Anyone who has taken opioids - prescription painkillers, methadone, certain cough or diarrhea medications, or street drugs - in the past 7 to 10 days: your doctor will test first, and taking naltrexone with opioids aboard triggers sudden, severe withdrawal. During treatment, opioids will not work at normal doses - and large doses trying to break through the blockade can cause serious injury, coma, or death. After treatment ends, your opioid sensitivity is higher than before - tell every future prescriber you were on naltrexone. Flag depression and kidney disease. If you become pregnant, call your doctor.
When is it an emergency?
Hallucinations, confusion, or any sign of opioid use breaking through - extreme drowsiness, slow breathing - is a 911 call. If you or someone near you may be in crisis, the 988 Suicide and Crisis Lifeline (call or text 988) is free, confidential, and 24/7. For an overdose, call Poison Control at 1-800-222-1222. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
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Common questions
Why did they test me before starting naltrexone?
Because of the 7-to-10-day rule: any opioid in your system - painkillers, methadone, certain cough or diarrhea medications, street drugs - plus naltrexone equals sudden, severe withdrawal. MedlinePlus says your doctor may order tests for recent opioid use before the first dose, and will not start it if opioids turn up. The washout window is the safety margin, not a technicality.
Why do they say opioids can kill me on naltrexone?
Two mechanisms, both from MedlinePlus. During treatment: naltrexone blocks opioid effects, so you may feel nothing at normal doses - and taking larger doses to override the block can cause serious injury, coma, or death. After treatment: your old tolerance is gone, so a dose your body once handled can now stop your breathing. Tell every prescriber, during and after, that naltrexone is or was in your life.
Why do I still need counseling if the pill blocks cravings?
The pill handles chemistry; it does not handle the reasons, the habits, the stress, or the people. MedlinePlus is explicit: naltrexone is only helpful as part of an addiction treatment program - counseling sessions, support meetings, education programs. Medication-plus-support outperforms either alone by a wide margin. The tablet makes the work possible; the work makes the sobriety durable.
Will naltrexone help with withdrawal symptoms?
No - the opposite. MedlinePlus states it does not prevent or relieve withdrawal symptoms and can cause or worsen them, which is why it starts only after withdrawal has passed. Withdrawal management is a separate phase with separate medications. Naltrexone's phase is the one after: staying stopped.
How long do I stay on naltrexone?
As long as it is helping - and it only helps while you take it, per MedlinePlus, which is why "continue even if you feel well" is written into the instructions. Months to years is normal, decided with your treatment team. The day you stop, two things matter: the protection against cravings stops, and your opioid sensitivity is higher than before treatment - both are prescriber conversations, not solo decisions.
What happens if I miss a dose of naltrexone?
Take it as soon as you remember, unless it is almost time for the next one - then skip it and never double up. On a supervised clinic schedule, a missed visit is a phone call to the clinic - the supervised dosing exists because gaps are where relapse lives, and the team would rather reschedule than lose the thread.