The standard dose of naltrexone for alcohol use disorder is 50 mg taken once daily as an oral tablet. It’s also available as a monthly injection. But how you start, when you take it, and what to expect along the way all matter for getting the most benefit with the fewest side effects.
How Naltrexone Works for Alcohol
When you drink, your brain releases natural opioid-like chemicals (endorphins) that trigger a surge of dopamine, the neurotransmitter tied to pleasure and reward. That dopamine hit is a big part of what makes alcohol feel rewarding and what drives the urge to keep drinking. Naltrexone blocks the receptor where those endorphins land, specifically the mu-opioid receptor. With that receptor blocked, drinking simply doesn’t produce the same pleasurable buzz it normally would.
This does two things. It reduces the reward you feel while drinking, which makes it easier to stop after one or two drinks instead of continuing. And it dulls cravings triggered by environmental cues, like walking past a bar or being at a party where others are drinking. Naltrexone doesn’t make you sick if you drink (that’s a different medication, disulfiram). It just makes alcohol less appealing.
Oral Tablets: Daily Dosing
The FDA-approved dose is one 50 mg tablet per day. Most prescribers, however, don’t start you at the full dose right away. A common approach is to begin with a quarter tablet (12.5 mg) or half tablet (25 mg) for the first one to two weeks, then increase to the full 50 mg. This ramp-up period helps your body adjust and reduces the chance of nausea, which is the most common early side effect.
Women, younger patients, and people who haven’t been abstinent from alcohol for very long are especially likely to benefit from this slower start. Taking the tablet with food also helps with nausea. A light meal or snack is usually enough.
When to Take It During the Day
Naltrexone starts working within about an hour of swallowing it and reaches peak levels in one to two hours. Its craving-reducing effects are most noticeable in the six to ten hours after a dose. This means timing matters.
Most clinicians suggest taking it in the morning with breakfast. This covers daytime and early evening cravings while also reducing nausea by pairing the dose with food. If your drinking pattern tends to hit hardest in the late evening, a late-afternoon dose may work better, though this can sometimes interfere with sleep. Taking it with a full glass of water and avoiding sugary or heavy drinks right around dosing time can also ease stomach discomfort.
Some people use naltrexone only on days they plan to drink rather than daily. This “as-needed” approach, sometimes called the Sinclair Method, involves taking a tablet about one to two hours before your first drink. While this method has supporting research, the FDA-approved protocol is daily dosing. Your prescriber can help you decide which approach fits your situation.
The Monthly Injection
If taking a daily pill feels like a hassle or you’re concerned about sticking with it, there’s an extended-release injectable version (brand name Vivitrol). A healthcare provider administers 380 mg as a single intramuscular injection once every four weeks. You don’t need to remember a daily dose, and the medication stays active in your system for the full month. The injection goes into the gluteal muscle, alternating sides each month.
A meta-analysis of clinical trials found that the injectable form reduced drinking days by about two per month and heavy drinking days by about 1.2 per month compared to placebo. Trials that ran longer than three months and didn’t require patients to be abstinent beforehand showed even larger effects: roughly two fewer heavy drinking days per month.
Common Side Effects
The most frequently reported side effects are nausea, headache, dizziness, fatigue, and anxiety. Nausea tends to be worst in the first week or two and often fades as your body adjusts, particularly if you start at a lower dose and take the medication with food. Some people also experience drowsiness or trouble sleeping, and occasional vomiting.
These side effects are generally mild enough that most people can continue treatment through them. If nausea is persistent, dropping back to 25 mg for another week before trying 50 mg again is a standard adjustment.
Important Safety Requirements
Naltrexone blocks opioid receptors. If you’ve recently used any opioid, whether a prescription painkiller, heroin, or a medication like methadone or buprenorphine, taking naltrexone can throw you into sudden, severe withdrawal. You need to be completely opioid-free for 7 to 10 days after short-acting opioids and 10 to 14 days after long-acting opioids before your first dose. This applies every time you restart after a gap in treatment, too.
Liver health is the other key concern. Naltrexone is processed by the liver, and cases of elevated liver enzymes and, rarely, liver inflammation have been reported. Most prescribers will check your liver function with a blood test before starting treatment and periodically afterward. If your liver enzymes are already three to five times above normal levels, naltrexone is generally not prescribed.
While you’re on naltrexone, standard opioid painkillers won’t work effectively because the receptor is blocked. If you need pain management for surgery or an emergency, make sure every healthcare provider treating you knows you’re taking naltrexone. Non-opioid pain relief options exist, but this requires planning.
How Long Treatment Typically Lasts
There’s no single fixed timeline. Many treatment plans run for at least three to six months, with some people continuing for a year or longer. The clinical trials showing the strongest benefits tended to be those lasting beyond three months. Naltrexone works best when combined with some form of counseling or behavioral support, not as a standalone solution.
Stopping naltrexone doesn’t cause withdrawal the way stopping alcohol or opioids does. But cravings can return, so the decision to taper off is usually based on how stable your drinking patterns have become, the strength of your coping strategies, and whether environmental triggers are well managed. This is a conversation to revisit regularly with whoever is prescribing it rather than a decision to make on your own based on feeling better.