Naltrexone Dosage: Label Doses for Alcohol, Opioids and Vivitrol, and What's Off-Label

Naltrexone dosage at a glance

50 mg is the only tablet strength in the FDA's drug directory

Every single-ingredient naltrexone tablet in the FDA's National Drug Code directory is a 50 mg film-coated tablet. The other listings are bulk powder, extended-release injection kits, and Contrave.³ Drugs@FDA also shows 25 mg and 100 mg naltrexone tablets approved for one maker, but neither strength appears in the directory's current listings.¹⁰ The original brand, ReVia, is no longer sold, so the tablets you get are generic naltrexone hydrochloride.^3,5

In clinical studies, one 50 mg tablet blocked the effects of 25 mg of injected heroin for up to 24 hours. Other data suggest that twice the dose blocks for 48 hours and three times the dose for about 72 hours.¹ Those numbers are the basis for the supervised schedules below. How long the drug itself lasts is a separate question, covered in how long naltrexone stays in your system.

The 25 mg starting dose for opioid use disorder is half a tablet.¹¹ The SpecGx tablet has a full score line across the middle.¹ Other makers' tablets may differ, so ask your pharmacist whether yours can be split.

Alcohol use disorder: one 50 mg tablet a day

The tablet label and the VA/DoD guideline both give this dose for most people.^1,4 The alcohol trials behind the label used it for up to 12 weeks, and "other dose regimens or durations of therapy were not evaluated" in them.¹

Higher doses appear in research. COMBINE, a US trial of 1,383 people who had recently stopped drinking, gave 100 mg a day for 16 weeks and found naltrexone lowered the risk of a heavy drinking day.¹² That is twice the label dose, and the label does not list it for alcohol. How naltrexone compared with acamprosate in that trial is on naltrexone vs acamprosate. How COMBINE fits with the other trials is shown on naltrexone success rates.

Starting on the shot. People should not be actively drinking at the first Vivitrol injection, and naltrexone does not ease alcohol withdrawal symptoms.²

For the wider picture of alcohol treatment, see naltrexone for alcohol use disorder.

Opioid use disorder: opioid-free first, then 25 mg

Naltrexone can set off sudden (precipitated) withdrawal in anyone who still has opioids in their body. That includes people taking it for alcohol who also use opioids.¹ So both forms start after an opioid-free gap:

No test is completely reliable for showing someone has been off opioids long enough. A naloxone challenge (a small dose of naloxone given to check for withdrawal) can help. If it brings on withdrawal, the label says not to start yet and to repeat the challenge in 24 hours.¹ What sudden withdrawal looks like is covered in naltrexone side effects.

The label then starts with 25 mg. If no withdrawal signs appear, the dose goes to 50 mg a day, which blocks injected opioids well enough.¹ The smaller first dose may reduce nausea, and 50 mg can start on day 2.¹¹

The tablet works for opioid use disorder "only when given as part of a comprehensive plan of management" that includes some way of making sure doses are taken.¹ A SAMHSA prescriber advisory says research shows the monthly shot's "treatment outcomes are far superior to oral naltrexone, which makes it the preferred antagonist for treating OUD."¹⁸

Supervised schedules use bigger doses on fewer days

When someone watches each dose being taken, the tablet label allows three other patterns: 50 mg on weekdays with 100 mg on Saturday, 100 mg every other day, or 150 mg every third day.¹

TIP 63 describes a three-day week adding up to 350 mg, such as 100 mg on Monday and Wednesday and 150 mg on Friday, which a spouse can observe.¹¹

These schedules have two trade-offs. With longer gaps between doses, the opioid block may be weaker. And single doses above 50 mg may carry a higher risk of liver injury.¹

Taking too much. In one study, people who took 800 mg a day for up to a week showed no signs of toxicity. Liver risk grows with dose over longer periods, though. At 300 mg a day in a placebo-controlled study, 19% (5 of 26) developed raised liver enzymes, against none on placebo.¹

Vivitrol is one 380 mg dose every 4 weeks

Vivitrol is naltrexone in slow-release microspheres. A health care provider gives it as a deep injection into the buttock muscle every 4 weeks or once a month, switching sides each time.² The 380 mg vial is the only strength sold.²

A 190 mg dose was tested in the main alcohol trial. It cut heavy drinking days by 17%, which missed statistical significance, while 380 mg cut them by 25%.¹⁹

Other label points on the shot²:

• No trial run on tablets is needed first.
• The opioid-free gap matches the tablet's.
• Switching from tablets to the shot has not been studied in a systematic way.
• One shot blocks opioids for about 28 days.

Amneal sells an unbranded Vivitrol kit under the same approval, with the same dosing.²⁰ For more on the shot, see Vivitrol and naltrexone vs Vivitrol.

What to do after a missed dose

Tablets. The tablet label has no missed-dose instruction, and MedlinePlus says to take a missed dose when you remember.¹ If it is almost time for the next one, skip the missed dose and carry on as usual. Don't take a double dose to make up.⁵

Vivitrol. If a shot is missed, the next one should be given as soon as possible.² There are no data on restarting after a long gap, and the person must be opioid-free again first.² TIP 63 says people treated for opioid use disorder can restart after 7 to 14 days without opioids.¹¹

Why gaps matter with opioids. The opioid block fades after a missed tablet and toward the end of each month on the shot. Overdose risk is higher then. Both labels tell prescribers to make sure patients and caregivers know about overdose-reversal drugs such as naloxone and can get one.^1,2 How the two drugs differ is explained on naltrexone vs naloxone.

Liver and kidney disease call for caution but few dose rules

The tablet label has no dose-adjustment table. The Vivitrol label is more specific, and the guidelines fill some gaps.

Liver tests. Both guidelines check liver tests before starting and then from time to time: every 6 or 12 months in TIP 63, and at 6 and 12 months, then yearly, in VA/DoD.^4,11 How other guidelines schedule liver tests, and the signs of liver injury, are on naltrexone liver tests.

Age. Safe use under 18 has not been established.¹ Vivitrol's trials included few people over 65. Kidney function tends to drop with age, so its label says checking it may be useful in older adults.²

Targeted dosing (the Sinclair method) is off-label

The US label dose is daily.¹ The Sinclair method uses the same 50 mg tablet another way. In Sinclair's Finnish protocol, people took it about 1 hour before drinking, and only on days they drank.⁶ Four targeted trials also used 50 mg, each with its own trigger:

• Daily for 12 weeks, then only when craving alcohol for 20 weeks (Finland, 121 people)²²
• Before situations people judged high-risk for heavy drinking (two US trials, 153 and 163 people)^23,24
• Targeted use in a 120-person US trial, where the median participant took it about 2.5 days a week²⁵

What those trials found, and why the method's best-known success figure is not a trial result, is on our Sinclair method page. The opioid-free rule applies to targeted use too.¹ Opioid-blocking drugs also do not block the loss of coordination that comes with drinking.⁶ For when to take a tablet around drinking, see drinking on naltrexone.

Low-dose naltrexone has no approved product

No low-dose naltrexone product is FDA-approved, so every LDN use in the US is off-label.³ LDN doses come from small trials. An adult Crohn's disease trial used 4.5 mg a day for 12 weeks. A fibromyalgia trial used 6 mg a day for 12 weeks and did not beat placebo on its main pain measure.^7,8 Across naltrexone studies in general, doses have ranged from 3 mg to 250 mg.²⁶ We found no primary source for an LDN titration schedule. The evidence by condition is on low-dose naltrexone. For medicine and surgery cautions at these off-label doses, far below the 50 mg tablet, see what to avoid on LDN.

For weight loss, the approved product is Contrave

Plain naltrexone is approved for alcohol dependence and for blocking opioids. Using it alone for weight loss is off-label.¹ Contrave combines naltrexone with bupropion in 8 mg/90 mg extended-release tablets. Its label raises the dose each week until week 4, when it reaches two tablets twice a day (32 mg of naltrexone). The tablets should not be cut, chewed or crushed. Stopping is advised if weight has not dropped at least 5% after 12 weeks on the full dose. Contrave should not be taken with other naltrexone products.⁹ Separate naltrexone and bupropion tablets, and Contrave's safety rules, are covered on naltrexone and bupropion.

How long to take it, and stopping

How long. No label sets a maximum. When to expect a change, and when guidelines say to judge it, is on how long naltrexone takes to work.

• Alcohol, after a 12-week trial: in a 6-month follow-up, some benefits lasted after the pills stopped, but the effect on staying abstinent held only through the first month. Longer treatment may help some people.²⁷
• A check-in point, not an end date: the VA/DoD guideline suggests considering stopping or switching to another option if 3 months on 50 mg a day brings no clear benefit.⁴
• Opioid use disorder: the best length of tablet treatment is unknown. People on the shot can stay on it as long as it helps and they want to continue. TIP 63's expert panel calls arbitrary time limits on the shot inappropriate.¹¹

Stopping. Naltrexone does not cause physical or psychological dependence, and neither label gives a taper schedule.^1,2 MedlinePlus advises against stopping without talking to your doctor first.⁵ After opioid use, tolerance is lower than before, so using opioids after stopping can lead to overdose.¹ If you have surgery coming up, see stopping naltrexone before surgery.

Naltrexone needs a prescription but is not a controlled substance.^1,28 See is naltrexone a controlled substance? To compare online prescribers and prices, see where to get naltrexone online and naltrexone cost.

Your experience: If you've taken naltrexone on a daily, targeted or monthly-shot schedule, you can share your story on our naltrexone reviews page.

How we checked

• Doses come from the current tablet and Vivitrol labels (May 2026), SAMHSA's TIP 63 and alcohol advisory (2021), the VA/DoD 2021 dosing table, the APA 2018 guideline statements and NIAAA.^{1,2,4,11,15,18,21}
• Tablet missed-dose and time-of-day advice comes from MedlinePlus, the National Library of Medicine's drug guide.⁵
• Every dose, blocking time and opioid-free gap was checked against the saved labels and TIP 63 on October 17, 2026; where TIP 63 says one tablet blocks for 72 hours, we used the label.