Naltrexone is a proven medication for alcohol and opioid addiction, though its effectiveness varies considerably depending on the substance involved, the formulation used, and whether a person can get through the often-difficult initiation phase. For alcohol use disorder, it works best at reducing heavy drinking days and cravings rather than enforcing total abstinence. For opioid use disorder, the long-acting injectable form roughly doubles six-month treatment retention compared with daily pills, but getting started on it is harder than starting buprenorphine, the main alternative. The picture gets more interesting when you look at the conditions where naltrexone is being tested but not yet standard practice, from gambling disorder to methamphetamine dependence, and when you factor in genetics that seem to sort people into responders and non-responders.
How It Works in Plain Terms
Naltrexone blocks opioid receptors in the brain, particularly the mu-opioid receptor. When you drink alcohol, your brain releases endorphins that bind to those receptors and produce a pleasurable buzz. Naltrexone sits on those receptors first, so the reward signal is dampened. You still feel the alcohol’s sedative effects, but the euphoric lift is muted. Over time, this blunting of reward weakens the learned association between drinking and pleasure, which reduces cravings and makes it easier to stop after one or two drinks instead of spiraling into a binge.
For opioid use disorder, the mechanism is more straightforward: naltrexone physically blocks heroin, fentanyl, or prescription opioids from activating the same receptors. If someone relapses while on naltrexone, they feel little to no high. That knowledge alone can deter use. The drug is approved at standard doses of 50 to 150 mg per day for both alcohol and opioid use disorders, though it is also available as a monthly injection (extended-release naltrexone, sold as Vivitrol) that removes the daily compliance problem.
Naltrexone for Alcohol Use Disorder
The evidence for naltrexone in alcohol dependence is solid, but it helps in a specific way. A meta-analysis comparing naltrexone with acamprosate, the other major medication for alcohol use disorder, found that naltrexone had a larger effect on reducing heavy drinking and craving, while acamprosate was better at helping people stay completely abstinent.1PubMed Central. Meta-analysis of naltrexone and acamprosate for treating alcohol use disorders: when are these medications most helpful? In practical terms, naltrexone is the better choice for someone whose goal is to cut back on dangerous drinking, while acamprosate may be a better fit for someone who has already stopped and wants to stay stopped.
One of the more useful findings is that naltrexone does not require full detoxification before you start it. A clinical trial of 121 people who were still actively drinking found that those who received naltrexone alongside cognitive coping skills had the best outcomes, and that a “targeted” approach, taking the medication only when craving hit, was effective at maintaining reduced drinking over a 20-week follow-up period.2PubMed. Targeted use of naltrexone without prior detoxification in the treatment of alcohol dependence: a factorial double-blind, placebo-controlled trial This finding has been replicated and expanded on, leading some researchers to propose that naltrexone should be given to people who are still drinking, with instructions to take it specifically when they anticipate drinking.3Alcohol and Alcoholism. Evidence about the use of naltrexone and for different ways of using it in the treatment of alcoholism This approach, sometimes called the Sinclair Method, reframes naltrexone not as a medication you take while abstinent but as a tool that gradually extinguishes the pleasure response to alcohol over months of targeted use.
Naltrexone for Opioid Use Disorder
Using naltrexone for opioid addiction presents a paradox: the drug works well once it is on board, but getting someone onto it safely is the hard part. Because naltrexone blocks opioid receptors, giving it to someone who still has opioids in their system triggers severe withdrawal, sometimes within minutes.4PubMed. Withdrawal syndrome caused by naltrexone in opioid abusers That means a person needs to be fully detoxified, typically seven to ten days opioid-free, before starting. During that gap, relapse risk is extremely high, and many people never make it to the first dose.
The landmark X:BOT trial, a large randomized comparison of extended-release injectable naltrexone and buprenorphine-naloxone, captured this problem clearly. Only about 72% of participants assigned to naltrexone successfully received their first injection, compared with 94% who started buprenorphine. Looking at all participants who were randomly assigned, relapse rates at 24 weeks were higher for naltrexone (65%) than buprenorphine (57%), and almost all of that gap was explained by early relapse among people who never got through induction. Among those who did successfully start, the two medications performed equally well.5PubMed Central. Comparative effectiveness of extended-release naltrexone versus buprenorphine-naloxone for opioid relapse prevention (X:BOT): a multicentre, open-label, randomised controlled trial
That “once you’re on it, it works” pattern has shown up in other studies as well. A separate randomized trial found that patients receiving extended-release naltrexone had a substantially lower risk of relapse to illicit opioids compared with those on buprenorphine-naloxone over longer follow-up, with the naltrexone group showing a stable low relapse risk over time.6PubMed. Risk of Relapse Among Opioid-Dependent Patients Treated With Extended-Release Naltrexone or Buprenorphine-Naloxone: A Randomized Clinical Trial The difference from the X:BOT findings likely reflects study design, setting, and how induction was handled, but the broader point holds: naltrexone is not inferior to buprenorphine pharmacologically, it is inferior logistically.
Why the Injectable Version Changes the Equation
Oral naltrexone for opioid addiction has a grim track record for adherence. A large meta-analysis and meta-regression found that about half of people on oral naltrexone dropped out within the first month, rising to roughly 61% by three months and 71% by six months. The injectable formulation had much better retention: about 26% dropped out at one month and 47% at three months.7PubMed Central. Factors associated with the percentage of individuals who initiate and discontinue naltrexone as a relapse prevention pharmacotherapy in opioid use disorder: A systematic review, meta-analysis and meta-regression One key reason is obvious: a pill can be skipped when cravings hit, but an injection received at a clinic lasts about 30 days regardless of what the person decides on any given morning.
A randomized trial directly comparing the two formulations found that patients receiving the injectable form had twice the rate of six-month treatment retention compared with those on daily pills.8PubMed Central. A Randomized Trial Comparing Extended-Release Injectable Suspension and Oral Naltrexone, Both Combined With Behavioral Therapy, for the Treatment of Opioid Use Disorder This matches what clinicians have observed for years: the pharmacology is fine, but relying on daily self-administration in a population fighting intense cravings is asking for trouble.
Supervised administration also improved oral naltrexone retention significantly, cutting dropout at three and six months by a meaningful margin compared with unsupervised use.7PubMed Central. Factors associated with the percentage of individuals who initiate and discontinue naltrexone as a relapse prevention pharmacotherapy in opioid use disorder: A systematic review, meta-analysis and meta-regression For people who cannot access the injectable version, having someone, whether a family member, pharmacist, or clinic worker, observe them taking the pill each day is the next best thing.
Does Naltrexone Prevent Overdose?
This is where the evidence gets thin and a bit concerning. While naltrexone blocks the high from opioids, the question of whether it actually prevents fatal overdoses has not been answered as clearly as you might expect. A study of commercially insured patients in the United States found that buprenorphine was associated with a roughly 60% reduction in opioid-related overdose compared with no treatment, but neither extended-release injectable naltrexone nor oral naltrexone showed a statistically significant reduction.9Drug and Alcohol Dependence. Overdose following initiation of naltrexone and buprenorphine medication treatment for opioid use disorder in a United States commercially insured cohort That does not necessarily mean naltrexone fails at overdose prevention. It could reflect the fact that people on naltrexone tend to drop out sooner, and the period after discontinuation is when overdose risk spikes, because tolerance has dropped while the person was on the medication. There was no association with overdose within four weeks of stopping any medication, but the confidence intervals were wide enough to leave room for concern.
This toleranace issue deserves emphasis. A person who has been on naltrexone for weeks or months has a dramatically lower opioid tolerance than before treatment. If they stop the medication and relapse at their old dose, the risk of fatal respiratory depression is substantial. This is not unique to naltrexone, but the abruptness of the tolerance loss makes it especially important for patients and families to understand.
Genetics and Who Responds Best
Not everyone responds to naltrexone equally, and a growing body of research suggests that a specific genetic variation in the mu-opioid receptor gene, known as the A118G polymorphism, helps predict who will benefit most. A meta-analysis of studies in alcohol-dependent patients found that naltrexone-treated people carrying at least one copy of the G allele had about twice the odds of avoiding relapse compared with those who were homozygous for the A allele.10PubMed. Association of µ-opioid receptor (OPRM1) gene polymorphism with response to naltrexone in alcohol dependence: a systematic review and meta-analysis A separate study in heavy drinkers confirmed this pattern: naltrexone-treated participants carrying the G allele had significantly more non-hazardous drinking days, while among those without the G allele, naltrexone performed no better than placebo.11PubMed Central. Variation in Mu-Opioid Receptor Gene (OPRM1) as a Moderator of Naltrexone Treatment to Reduce Heavy Drinking in a High Functioning Cohort
Brain imaging work has added another layer: naltrexone-treated individuals with the G allele showed reduced activation in brain reward regions when exposed to alcohol cues, and that effect was further modified by variation in a dopamine transporter gene.12Neuropsychopharmacology. Interacting Effects of Naltrexone and OPRM1 and DAT1 Variation on the Neural Response to Alcohol Cues In plainer terms, the drug seems to quiet down the brain’s “want” circuits more effectively in people with a certain genetic profile. This is among the strongest examples of pharmacogenomics in addiction medicine. Whether routine genetic testing before prescribing naltrexone is worth the cost is still debated, but the science is strong enough that some clinicians check for it, especially when a first trial of naltrexone produces no noticeable benefit.
Combining Naltrexone With Therapy
Naltrexone works better when paired with structured behavioral therapy, particularly cognitive behavioral therapy. A randomized trial found that the combination of naltrexone and CBT outperformed naltrexone with other therapeutic approaches: fewer patients in the CBT-naltrexone group relapsed, and those who did had both fewer relapses and more time between them.13PubMed. Naltrexone combined with either cognitive behavioral or motivational enhancement therapy for alcohol dependence A broader meta-analysis of pharmacotherapy combined with behavioral therapy for substance use disorders supported this pattern, concluding that clinicians should favor CBT over basic clinical management when prescribing addiction medications to optimize outcomes.14JAMA Network Open. Combined Pharmacotherapy and Cognitive Behavioral Therapy for Adults With Alcohol or Substance Use Disorders: A Systematic Review and Meta-analysis
This finding is consistent with the mechanism. Naltrexone blunts the reward signal, but it does not teach a person new coping strategies for stress, social pressure, or emotional triggers. CBT fills that gap. In clinical practice, the most common setup is monthly injection visits combined with weekly or biweekly therapy sessions, though access to that full package depends heavily on insurance and geography.
Safety and the Liver Myth
A persistent concern about naltrexone is liver damage. The drug’s label has long carried a black-box warning about hepatotoxicity, based on early studies that used much higher doses than are now standard. This warning has scared clinicians away from prescribing it to exactly the patients who need it most: heavy drinkers, many of whom already have liver disease. Recent evidence suggests the fear is overblown. A systematic review and meta-analysis of randomized trials found no increased risk of serious adverse events for naltrexone compared with placebo across nearly 5,000 participants. The six adverse events that were marginally more common with naltrexone were mild in severity.15PubMed Central. Serious adverse events reported in placebo randomised controlled trials of oral naltrexone: a systematic review and meta-analysis
More striking, a large study of patients with underlying liver disease, including those with compensated cirrhosis, found that liver enzyme levels actually went down after starting naltrexone, not up, likely because people were drinking less.16PubMed Central. Naltrexone for alcohol use disorder: Hepatic safety in patients with and without liver disease A separate study focused specifically on patients with cirrhosis found that only 2% had any liver enzyme elevations during the high-risk window, and none of those cases qualified as even possible drug-induced liver injury. No deaths or new decompensations were attributed to naltrexone.17JHEP Reports. Safety of naltrexone in patients with cirrhosis The black-box warning has not been removed, but the clinical consensus has shifted: naltrexone is safe for people with liver disease, and withholding it out of hepatotoxicity fears may do more harm than good.
The most common side effects at standard doses are nausea, headache, dizziness, and fatigue. These tend to be worst in the first week or two and usually fade. Injection-site reactions, including pain, hardness, or occasionally abscess, affect a minority of patients receiving the monthly shot.
Beyond Alcohol and Opioids
Naltrexone is being used, with varying levels of evidence, for several other conditions that involve reward-seeking behavior. Gambling disorder is one of the better-studied applications. A double-blind trial found that 75% of participants taking naltrexone were rated as “much” or “very much” improved at the end of the study, compared with 24% on placebo.18Biological Psychiatry. Double-blind naltrexone and placebo comparison study in the treatment of pathological gambling A UK case series found that 60% of treated patients abstained from gambling entirely, with another 20% reducing their gambling to near-zero.19PubMed Central. The use of naltrexone in pathological and problem gambling: A UK case series A network meta-analysis of pharmacological treatments for gambling disorder concluded that naltrexone and the related drug nalmefene have the strongest evidence base, though both also caused notably higher dropout rates due to side effects.20Comprehensive Psychiatry. Pharmacological management of gambling disorder: A systematic review and network meta-analysis
Binge eating disorder has drawn interest as well. A study of adolescents in an eating disorder program found that about two-thirds showed a positive response to naltrexone, with reduced purging and reduced urge to purge.21PubMed Central. Naltrexone Reduces Binge Eating and Purging in Adolescents in an Eating Disorder Program A laboratory study of naltrexone combined with bupropion found that the combination reduced calories consumed, craving, and hunger in people with binge eating disorder.22Drug and Alcohol Dependence Reports. Naltrexone/bupropion for binge-eating disorder: A human laboratory investigation of mechanisms That combination, marketed as Contrave for weight loss, uses a much lower dose of naltrexone than standard addiction treatment.
Methamphetamine dependence is one of the most desperate areas for new treatments, since no medication is currently approved for it. A large trial found that the combination of naltrexone and bupropion produced a response rate of about 14%, compared with roughly 2.5% for placebo.23PubMed Central. Bupropion and Naltrexone in Methamphetamine Use Disorder Those numbers sound low, but in a field with essentially zero approved options, any treatment that outperforms placebo by that margin is worth attention. Lab studies have shown that naltrexone blunts the craving and pleasurable effects of methamphetamine, suggesting the opioid system plays a larger role in stimulant reward than previously thought.24Neuropsychopharmacology. The Effects of Naltrexone on Subjective Response to Methamphetamine in a Clinical Sample: a Double-Blind, Placebo-Controlled Laboratory Study Naltrexone has also shown reductions in craving and self-reported amphetamine use in a separate placebo-controlled trial.25PubMed. Naltrexone for the treatment of amphetamine dependence: a randomized, placebo-controlled trial
Practical Barriers to Getting Started
Even when naltrexone is the right clinical choice, logistical obstacles can derail treatment. The injectable form costs substantially more than the oral version and requires cold-chain storage, meaning clinics need a dedicated refrigerator and trained staff for intramuscular injection. A qualitative analysis of provider-level barriers found that the complexity of ordering and administering the medication, plus inconsistent insurance coverage and reimbursement, discouraged its use even when clinicians believed it would help their patients.26Journal of Substance Abuse Treatment. Extended-Release Naltrexone: A Qualitative Analysis of Barriers to Routine Use
For opioid use disorder, the detox requirement is the biggest practical hurdle. A person must be free of opioids for enough days that precipitated withdrawal will not occur, and during that waiting period, many people relapse or simply do not return. Research continues into better induction protocols, including low-dose naltrexone bridging strategies and rapid induction under sedation, but no single approach has emerged as the standard.27PubMed Central. Long-Acting Injectable Naltrexone Induction: A Randomized Trial of Outpatient Opioid Detoxification With Naltrexone Versus Buprenorphine This is why buprenorphine, which can be started while a person is still in mild withdrawal, is often the default first-line choice in emergency departments and walk-in clinics. Naltrexone works best in structured settings where the transition from active use to full opioid clearance can be supported.
Low-Dose Naltrexone Is a Different Story
You may have encountered claims about low-dose naltrexone (typically 1 to 5 mg per day) for chronic pain, autoimmune conditions, or even mood disorders. This is a genuinely different pharmacological approach from standard-dose naltrexone for addiction. At low doses, the drug is thought to briefly block opioid receptors for a few hours, potentially causing a rebound increase in endorphin production, and may have anti-inflammatory effects through entirely separate pathways involving immune cells called microglia.28PubMed Central. The use of low-dose naltrexone (LDN) as a novel anti-inflammatory treatment for chronic pain Research using laboratory models found no evidence that low-dose naltrexone works through the endorphin-boosting mechanism often attributed to it in popular accounts, complicating the story further.29eNeuro. Reported Benefits of Low-Dose Naltrexone Appear to Be Independent of the Endogenous Opioid System Involving Proopiomelanocortin Neurons and β-Endorphin The point worth keeping straight is that low-dose naltrexone is not “naltrexone for addiction at a smaller dose.” The two uses appear to involve different mechanisms, and evidence from one does not transfer to the other.