Naltrexone: A Clinical Guide for Alcohol and Opioid Use Disorder

Naltrexone is one of the most-studied and least-used medications in addiction medicine. It is FDA-approved, non-addictive, and backed by decades of research, yet most people who could benefit from it never hear it mentioned. Fewer than 1 in 10 people with alcohol use disorder receive any FDA-approved medication for it, even though several effective options exist (NIAAA).

This guide explains what naltrexone does, how it differs from other medications, who it helps, and how it fits inside a complete treatment plan for alcohol use disorder (AUD) and opioid use disorder (OUD).

What is naltrexone and how does it work?

Naltrexone is an opioid-receptor antagonist. In plain terms, it sits on the receptors in your brain that opioids and alcohol act on, and it occupies them without switching them "on." Nothing about it produces a high.

For someone with opioid use disorder, that means opioids cannot trigger euphoria while naltrexone is active. For someone with alcohol use disorder, drinking feels flat: the reward that normally reinforces the next drink is dialed down. Over weeks of consistent use, this weakens the craving-and-reward loop that keeps the cycle going.

A key point worth repeating: naltrexone is not a controlled substance, you do not become dependent on it, and it has no street value or abuse potential (SAMHSA). This is what sets it apart from opioid-agonist medications like methadone or buprenorphine, which are also effective but work in a very different way.

Is naltrexone the same as a detox medication?

No. Naltrexone is not a treatment for withdrawal, and it does not replace medically supervised detox. In fact, starting it too soon can make things much worse, which is why timing matters so much for opioid use disorder.

What is the critical rule before starting naltrexone?

For opioid use disorder, the single most important rule is this: you must be opioid-free for a minimum of 7 to 10 days before your first dose. If naltrexone is given while opioids are still in your system, it can knock them off the receptors all at once and trigger precipitated withdrawal, which can be severe enough to require hospitalization (FDA).

People transitioning off methadone or buprenorphine may need to wait even longer. This is exactly why naltrexone is started under clinical supervision, usually after a medically managed detox, as part of medication-assisted treatment rather than on your own.

For alcohol use disorder, there is no washout period. A liver function check is standard before starting, but you do not need to wait out a drug-free window the way you do with opioids.

What are the two forms of naltrexone?

Naltrexone comes in two formulations, and the right one depends on the person.

• Oral tablet: Taken daily, inexpensive, and widely covered by insurance. The trade-off is that it relies on remembering a pill every day, and missed doses reduce its protection.
• Vivitrol (extended-release injection): Given once a month by a provider. It removes the daily decision entirely and blocks opioids for roughly 28 days per dose, which is a meaningful advantage for relapse prevention when daily adherence is hard.

Whichever form you use, naltrexone is not a quick course. Most clinicians recommend at least three to six months, and many people do best on twelve months or longer. Stopping early is the most common reason naltrexone seems "not to work" in real life.

How effective is naltrexone?

The evidence is strong, and it is worth being precise about what the research actually shows.

For alcohol use disorder, a large 2014 systematic review and meta-analysis published in JAMA pooled more than 120 trials and found that oral naltrexone at 50 mg per day meaningfully reduced return to drinking. The number needed to treat (NNT) to prevent one person from returning to any drinking was about 12, placing naltrexone among the better-supported medications for AUD (JAMA; AHRQ). An NNT of 12 means roughly one in twelve people treated gets a benefit they would not have had otherwise, which is a clinically useful result for a safe, non-addictive medication.

For opioid use disorder, extended-release naltrexone is FDA-approved to prevent relapse after detox. In head-to-head research, once a person is successfully started on it, extended-release naltrexone has performed comparably to buprenorphine-naloxone for preventing relapse (NIDA). The main real-world challenge is getting through the opioid-free window to that first injection.

What are the side effects and risks?

Most side effects are mild and tend to ease within one to two weeks. The more common ones include nausea, headache, dizziness, fatigue, nervousness, trouble sleeping, and, for the injection, soreness at the injection site (FDA).

Serious adverse events are uncommon, but two risks deserve real attention:

• Liver safety. Naltrexone is processed by the liver, so it is not used in severe liver disease or acute hepatitis. Providers check liver function before and sometimes during treatment.
• Reduced opioid tolerance. This is the one that can be life-threatening. After detox and while on naltrexone, your tolerance to opioids drops quickly. If someone relapses and uses the amount they once used, that dose can now cause a fatal overdose. This is why naloxone (overdose-reversal) kits and overdose-prevention counseling are essential parts of treatment (FDA).

When is naltrexone not the right choice?

Naltrexone is a good fit for many people, but not everyone. It is generally not appropriate when someone:

• Is still using opioids or is in the middle of withdrawal.
• Has severe liver impairment or acute hepatitis.
• Needs or prefers opioid-agonist therapy, where methadone or buprenorphine may be the better option for opioid addiction treatment.
• Has untreated mental health conditions such as PTSD or depression that need parallel care.
• Is pregnant or breastfeeding, where data are limited and decisions are individualized.

Choosing the right medication is a clinical decision made with your care team, not a one-size-fits-all rule.

What is the Sinclair Method?

You may come across the Sinclair Method, an approach where naltrexone is taken about an hour before drinking to pharmacologically "extinguish" the reward over time. It has a small evidence base in select populations, but it is an off-label dosing schedule that is not FDA-approved and remains uncommon in U.S. practice. If you are curious about it, it is a conversation to have with a clinician rather than something to try on your own.

How does naltrexone fit into recovery?

Medication is a tool, not a cure. Naltrexone removes a biological obstacle, the craving-and-reward loop, so that the rest of recovery becomes possible. It works best when it sits inside a fuller plan that includes counseling, peer support, a stable environment, and care for any co-occurring mental health or social factors.

That is how we approach it at Clear Steps Recovery. Naltrexone is offered as one part of alcohol addiction treatment and broader medication-assisted treatment, paired with therapy and a structured aftercare plan, because relapse risk is highest in the weeks right after a program ends. Our medical team, led by Dr. Richard Marasa, reviews every plan to match the medication, the form, and the length to the person.

As Dr. Marasa puts it: naltrexone does not replace the work of recovery. It removes a biological obstacle so the work of recovery becomes possible in the first place.

Talk to someone who can help

If you are wondering whether naltrexone or another medication-assisted option is right for you or a loved one, our admissions team can talk it through confidentially and without judgment, across New Hampshire and Massachusetts.