Naltrexone: What It Is Used For and How It Works

Naltrexone at a glance

Two approved uses, three off-label or combination uses

For alcohol, the American Psychiatric Association recommends offering naltrexone or acamprosate to people with moderate to severe alcohol use disorder who prefer medication or have not improved with other treatment.¹⁴ Disulfiram, off-label topiramate and the other pills to stop drinking are compared on their own page.

For LDN, a 2026 review of 105 studies found that early positive results from uncontrolled studies "were rarely replicated in placebo-controlled trials."¹¹

How naltrexone works: it blocks opioid receptors

Naltrexone attaches to the body's opioid receptors, most tightly to the mu receptor, and does not switch them on.³ It competes with opioids for those receptors. While it is in place, heroin and opioid painkillers have little or no effect. In studies, a 50 mg tablet blocked the effects of 25 mg of injected heroin for as long as 24 hours; doubling or tripling the dose stretched that to about 48 or 72 hours.²

The block can be overpowered. Someone who takes large amounts of opioids to get past it can have a fatal overdose.²

Alcohol. How naltrexone lowers drinking is not fully understood; animal research points to the body's own opioid system.² The working explanation is that it blocks the opioid receptors involved in the rewarding effects of drinking.⁵ In laboratory studies, people on naltrexone reported less craving and less stimulation from alcohol, and more sedation; the effects were small.¹⁵ What drinking feels like on it is covered on drinking on naltrexone, and the alcohol research on the AUD page.

What it does not do.

• It produces no high and no opioid effect, and it was not linked to tolerance or dependence.²
• It causes no Antabuse-like reaction to alcohol.²
• In someone dependent on opioids, it sets off withdrawal (see below).²

In the body. A tablet is absorbed quickly, with peak blood levels within an hour. The liver breaks down most of it on the first pass, and its main breakdown product, 6-beta-naltrexol, is also active.²

It helps with drinking modestly; for opioids the shot has the evidence

Alcohol. The tablet label sets expectations at "a modest improvement in the outcome of conventional treatment."² Across pooled trials, 11 people needed to take naltrexone for 1 more to avoid a return to heavy drinking, and the 95% confidence interval ran from 5 to 41.⁴ Across 50 trials, heavy drinking was 17% less likely on naltrexone, with no statistically significant effect on whether people drank at all.¹⁶

Opioids. A Cochrane review of 13 trials (1,158 people) found daily pills no better than placebo, except in studies where people were made to take them.⁶ In a placebo-controlled trial of the Vivitrol shot after detox, people on it had confirmed opioid-free results in a median 90% of weeks, against 35% on placebo.¹⁷

The trials, including the negative ones, are covered one by one on does naltrexone work? When to expect a change is covered on how long naltrexone takes to work.

The FDA has approved a tablet and a shot, nothing else

Tablets. Seven generic naltrexone tablet approvals are listed as prescription products in Drugs@FDA.⁸ Why 50 mg is the only strength you will see is explained on naltrexone dosage. Former tablet brands (ReVia, Depade) and each one's status are listed on naltrexone brand names.

The shot. Vivitrol is made by Alkermes. An unbranded version distributed by Amneal is sold under the same FDA approval, so it is not a generic.¹⁸ A true generic from Teva was approved in 2023 and is now listed as discontinued.⁸ Pill and shot are compared on naltrexone vs Vivitrol.

Implants. Naltrexone pellets placed under the skin are not FDA-approved in the US: naltrexone implant.

Compounded versions. LDN capsules and some telehealth formulations are made by compounding pharmacies. Compounded drugs are not FDA-approved, and the FDA does not check their safety, effectiveness or quality before sale.^12,19 How to tell them apart is explained on generic vs compounded naltrexone.

Opioids must be out of your system before the first dose

Opioids. Stop short-acting opioids, including tramadol, for at least 7 to 10 days first. After methadone or buprenorphine, withdrawal can be triggered for as long as 2 weeks.² Opioid cough, cold and diarrhea medicines count. A clinic may check with a urine test or a naloxone challenge, but the label says no method is completely reliable.² Withdrawal set off by naltrexone usually starts within 5 minutes, can last up to 48 hours, and has put people in hospital.² For opioid use disorder, the tablet label starts with 25 mg, then 50 mg a day if there are no withdrawal signs.²

Alcohol. Some patient pages still say you must stop drinking and finish detox before the first tablet. US guidance for clinicians says naltrexone "can be started while a patient is still drinking," and it can be continued after a relapse.^5,7 Vivitrol is different: its alcohol approval covers people who stop drinking before the first shot.³ If you drink heavily every day, stopping suddenly can be dangerous, so plan withdrawal with a clinician.

How long. England's NICE guideline starts the tablets after assisted withdrawal, stops them if drinking persists 4 to 6 weeks in, and otherwise prescribes them for up to 6 months, or longer if they are helping.²⁰ Missed doses and schedules are covered on naltrexone dosage.

Most side effects are mild; the serious risks involve opioids and the liver

In an open-label safety study of about 570 people treated for alcohol use disorder, the most common new side effects were nausea (10%), headache (7%), dizziness (4%), nervousness (4%) and tiredness (4%).² Overall, it is generally safe and well tolerated.⁷ The shot adds injection-site reactions.³ Rates against placebo, and what helps, are on naltrexone side effects and Vivitrol side effects.

• Overdose after stopping. Tolerance falls, so a smaller opioid dose than before can be fatal. Read the full warning and keep naloxone at home.²

• Liver. The label warns of hepatitis and liver injury. In placebo-controlled studies, doses up to 300 mg a day, several times the usual dose, injured the liver in a substantial share of people.² FDA removed the boxed liver warning from the ReVia tablet label in October 2013.²¹ See naltrexone liver tests.

• Mood. People taking it for alcohol or opioids should be watched for depression or suicidal thinking.² If you have thoughts of suicide, call or text 988.²²

• Medicines that may not work. Opioid painkillers, cough medicines and diarrhea medicines may have little effect. Carry a card saying you take naltrexone.² Taking it with disulfiram, which can also harm the liver, is not ordinarily recommended, and Contrave's label advises against adding other naltrexone products.^2,13

• Driving. It can cause dizziness, so wait to drive until you know how it affects you.²

Naltrexone is not naloxone, and it is not Suboxone

A tablet blocks opioids for about a day; the shot for about a month

Naltrexone's half-life is about 4 hours and 6-beta-naltrexol's about 13 hours.² One Vivitrol shot blocks opioids for about 28 days.³ Drug tests, surgery and the timing of the last dose are covered on how long naltrexone stays in your system.

Not a controlled substance, and no dependence in studies

Federal rules exclude naltrexone from the opioid schedule, so it carries none of the extra prescribing rules that apply to controlled drugs.⁹ It does not lead to physical or psychological dependence, and NIAAA lists it among the nonaddictive alcohol medicines.^2,25 It still needs a prescription. See is naltrexone a controlled substance? and is naltrexone addictive?

Any licensed prescriber can write it

No special license or registration is needed: any practitioner licensed to prescribe medicines can prescribe it.²⁶ NIAAA tells clinicians the alcohol medicines are "neither addicting nor complicated to prescribe," and that primary care can offer them.⁵ Yet in 2024, 2.5% of people in the US aged 12 and older with alcohol use disorder (about 697,000 of an estimated 28.0 million) received medication for it.^27,28

You can ask your own doctor, or compare 13 online programs, their prices and whether they use generic or compounded naltrexone on where to get naltrexone online. We have full reviews of Oar Health, Reframe, Ria Health and Sunnyside.

Naltrexone through the years

Every naltrexone page on this site

About the drug

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How we checked

• Drug facts come from the current tablet, Vivitrol and Contrave labels on DailyMed. Approval dates come from FDA application records and SAMHSA's TIP 63.^1-3,8,13
• Evidence comes from the 2023 AHRQ review, Cochrane reviews, one Vivitrol opioid trial and a 2019 laboratory meta-analysis, read as abstracts or summaries.^4,6,15-17
• Every figure was matched to a saved copy of its source on October 17, 2026.