Monthly Naltrexone Injection Outperformed Standard Care in Review

Anyone finishing medical detox from opioids faces a decision about how to proceed with their recovery care, and a Cochrane review of 22 trials gives it some shape. Compared to standard care, meaning counseling and referrals without medication, the monthly naltrexone injection reduced illicit opioid use. That is the clearest result in the review, and for someone weighing medication-assisted treatment after withdrawal, it is the one worth knowing first.

The comparisons against other medications are more complicated, and the review is careful about how much weight each one can carry.

Why Medical Detox Matters Here

Naltrexone is the one opioid use disorder medication that cannot be started during withdrawal. It is an antagonist, blocking opioid receptors rather than occupying them, and giving it to someone with opioids still in their system will trigger precipitated withdrawal, an abrupt and severe onset of symptoms.

That is why the trials recruited people in outpatient settings after residential treatment, detoxification, or incarceration. Naltrexone sits on the far side of detox, and getting there safely requires clinical supervision. Injected intramuscularly, it blocks opioid effects for about a month. Implant formulations can last up to six months but are not approved in the United States.

The window right after withdrawal is also the most dangerous one. Tolerance falls during detox, so if you relapse and return to your previous dose, you have a sharply elevated overdose risk. Whatever medication follows detox, the handoff is where planning matters most.

What the Review Found

The review, published in the Cochrane Database of Systematic Reviews in May 2025, identified 22 randomized trials with 3,416 participants. Nine compared sustained-release naltrexone with treatment as usual, six with placebo, five with oral naltrexone, three with opioid agonist treatment, and one with a psychosocial intervention.

Against treatment as usual, the injection reduced illicit opioid use, with a risk ratio of 0.72 and a number needed to treat of six, across four trials and 479 participants. It also reduced serious adverse events when treatment discontinuation, overdose, and death were pooled into one category, with a risk ratio of 0.59 and a number needed to treat of 14, across six trials and 1,009 participants.

Two caveats belong with that second figure. Analyzed separately rather than pooled, overdose and death showed no significant difference. And treatment as usual varied widely across the trials, with some studies offering participants little more than a list of community resources.

How Naltrexone Injections Compare With Methadone and Buprenorphine

Here the direction reverses. The review found moderate-certainty evidence that sustained-release naltrexone probably increases in-treatment illicit opioid use slightly compared with opioid agonist treatment, with a risk ratio of 1.15 in a single trial of 570 participants.

Moderate certainty is the highest confidence rating attached to any comparison in this review, so this is not a marginal finding. On retention in treatment and on how many patients accepted the treatment, the evidence against agonists was rated very uncertain. Serious adverse events may increase slightly, though that estimate carried low certainty and its confidence interval crossed the line of no effect.

For most people leaving detox, this points toward buprenorphine or methadone as the stronger first option.

Naltrexone Injection Versus Daily Pills

The injection also reduced illicit opioid use compared with oral naltrexone, with a risk ratio of 0.65. That fits the long-standing concern that a daily pill is hard to sustain and that missed doses erase the protection.

It is the thinnest result in the review, though. It rests on one trial of 69 participants at low certainty, so it should be read as consistent with expectation rather than as strong evidence.

Understanding Medication-Assisted Treatment Options

Buprenorphine is a partial opioid agonist and methadone is a full agonist. Both occupy opioid receptors, easing withdrawal symptoms and cravings without producing the effects of illicit opioids at therapeutic doses.

Naltrexone works in the opposite direction, blocking the receptor entirely. It carries no risk of dependence or diversion (misuse), and the monthly injection removes the daily adherence problem.

None of these types of medication-assisted treatment is a lesser form of recovery. Naltrexone remains a reasonable option for people who have completed withdrawal and prefer an antagonist, or who cannot take an agonist. The review argues for informed sequencing rather than against any medication. One more figure puts the whole comparison in perspective: of the 4.8 million people in the United States with opioid use disorder in 2024, only 17 percent received any medication for it.

Finding Medical Detox

If you are considering naltrexone, ask any program you contact how it handles the transition.

– Ask whether the program initiates medication-assisted treatment during or immediately after withdrawal management

– Ask how long it requires you to be opioid free before a naltrexone injection, and how it monitors for precipitated withdrawal

– Ask whether buprenorphine and methadone are also available, so the choice is actually a choice

– Ask what happens at discharge, since the post-detox window carries the highest overdose risk

Never attempt alcohol or benzodiazepine withdrawal without medical supervision, because withdrawal from either can be life threatening. Opioid withdrawal is rarely fatal on its own, but the overdose risk that follows it is why supervised detox and a planned medication handoff matter.

Detox.com’s directory lists medically supervised detox programs by state and city, filterable by level of care and medication offered.

If you are in crisis, call or text 988.