Naltrexone
Naltrexone blocks the receptors that make alcohol and opioids rewarding, so a drink or a dose just doesn't land the same — taken daily as a pill or monthly as a shot.
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Is Naltrexone the Right Way Off Opioids?
If you are weighing naltrexone, the medicine behind the monthly Vivitrol shot, you are already doing the hardest part: looking for a way out instead of a way to keep using. Here is the plain version. Naltrexone is an opioid blocker, not an opioid. It parks on the same receptors that heroin, fentanyl, and prescription painkillers act on and shuts the door, so if you do use, you feel little or nothing.
It carries no high of its own, which means there is nothing in it to get hooked on and nothing worth selling. That makes the old worry about “trading one addiction for another” simply not apply here.
There is one catch that decides almost everything, and an honest guide leads with it: you have to be fully off opioids before your first dose, or it throws you into sudden, severe withdrawal. Below is the whole picture, so you can have a real conversation with a provider instead of a guess.
- Naltrexone blocks opioids, it is not one. It occupies opioid receptors so other opioids cannot work, with no high, no abuse potential, and no street value.
- You must be fully opioid-free before the first dose. Starting too soon triggers sudden, severe withdrawal, so the usual wait is 7 to 10 days, longer for fentanyl, which means a medical detox is the on-ramp.
- Keep naloxone (Narcan) on hand. If you stop naltrexone and go back to opioids your tolerance is gone and overdose is more likely, and Narcan reverses it.
What Naltrexone Is and How the Block Works
Naltrexone is a competitive opioid antagonist — a precise way of saying it competes with opioids for the same docking points in the brain and wins[1]. When naltrexone is sitting on those mu-opioid receptors, a dose of heroin or oxycodone cannot attach. No euphoria, no sedation, no reward[1].
That is the opposite approach from the other two main opioid-addiction medicines. Buprenorphine (Suboxone) and methadone are agonists — they gently switch the receptors on, which is what calms cravings and withdrawal. Naltrexone never switches anything on. It does not ease cravings the way those medicines do; what it does is take the payoff out of using, so over time the pull to use tends to fade.
Why a Pure Blocker Has No Abuse Potential
Two things follow from naltrexone being a pure blocker, and both are genuine advantages:
- There is nothing to abuse and nothing to divert. Because there is no opioid in it, you cannot get high on naltrexone and it has no street value.
- Stopping it causes no withdrawal. Your body does not become dependent on it the way it does on an opioid, so the medicine itself is easy to be done with.
This is also why the “trading addictions” myth does not even apply to naltrexone. That worry gets aimed at methadone and buprenorphine because they are opioids; naltrexone is not one. It has no abuse potential at all, so the objection has nowhere to land.
One practical note: while naltrexone is in your system, standard opioid painkillers may not work, because the same blockade that stops a high also blocks pain relief. Animal research shows long-term naltrexone shifts how the body responds to opioids[2]. Tell any doctor or dentist you are on it, and wear a medical alert if you can.
The Monthly Shot Versus the Daily Pill
Naltrexone comes in two forms, and the difference is mostly about one thing: whether you have to remember it every single day. Adherence is what decides everything here.
Why Oral Naltrexone Often Falls Short
Oral naltrexone is a 50 mg tablet taken daily. It is cheap and easy to get, and when a person takes it, the block works. The trouble is real life. Daily pill-taking asks for daily motivation, and motivation comes and goes, especially early in recovery.
The large Cochrane review of oral naltrexone pooled thirteen studies and found it did not beat placebo on the main outcomes, with only about 28% of people staying in treatment[3]. The drug was not the failure. Sticking to it was.
How Vivitrol Solves the Adherence Problem
The injectable form, extended-release naltrexone sold as Vivitrol, was built to fix exactly that. It is a single shot into the muscle that keeps the receptors blocked for about a month, so the daily decision disappears for four weeks at a time[4].
That one change moves the numbers a lot:
- A randomized trial found the injection roughly doubled six-month retention compared with the daily pill — 57% versus 28%[5].
- The 2025 Cochrane review of 22 studies and 3,416 people likewise found the long-acting form holds people in treatment better than the oral one[6].
- The shot is only as good as showing up for it. In studies run on protocol, about 47% of people took every scheduled injection; in ordinary clinical records that dropped to about 10%[7].
The takeaway is simple: if naltrexone is the path you choose, the monthly Vivitrol injection is almost always the better version, because it removes the daily-adherence problem that sinks the pill. Oral naltrexone can still make sense for someone with strong outside accountability — a monitored professional, say — but for most people the shot is the one with the evidence behind it.
You Have to Be Fully Opioid-Free Before the First Dose
This is the part that decides whether naltrexone will fit you, so here it is straight. Because naltrexone shoves opioids off their receptors, taking it while you still have opioids in your body sets off precipitated withdrawal — a fast, brutal version of dope sickness that comes on harder than natural withdrawal.
To avoid that, you have to be genuinely off opioids before the first dose, usually 7 to 10 days, and longer for fentanyl, which lingers in the body’s fat and clears more slowly than heroin or pills.
The Opioid-Free Window Is the Real Barrier
That waiting period, not the medicine, is the obstacle. Getting through a week-plus of withdrawal before you are even allowed to start is hard, and many people never reach the first dose.
A systematic review made the gap plain:
- When people still had to detox first, about 63% got successfully started on the injection[7].
- When people were already detoxed, that jumped to about 85%[7].
The barrier also lands hardest on the people who are using most heavily. Outpatient initiation succeeds for roughly 74% of people whose main opioid was prescription pills, but only about 23% of people injecting heroin[8].
Detox Is the On-Ramp, Not a Dead End
The honest implication: if you are still actively using, getting onto naltrexone usually means a medical detox first — and doing that withdrawal in a supervised setting is far easier and safer than white-knuckling it at home. Medications can make withdrawal far gentler than the agony you are bracing for.
So if the opioid-free window is the thing standing between you and naltrexone, that is a reason to get into detox, not a reason to put off treatment. Detox is the on-ramp. Once you are through it, the door to naltrexone is open.
How Naltrexone Compares With Buprenorphine and Methadone
It helps to be direct about where naltrexone stands against the other medicines, because the differences are real and they shape your decision.
Once People Are On It, Naltrexone Works
When people get on naltrexone and stay on it, it does the job:
- It cuts illicit opioid use compared with no medication — strong, high-certainty evidence[6].
- A Norwegian trial that started everyone after detox found the Vivitrol shot about as effective as buprenorphine-naloxone on staying in treatment and on clean urine tests[9].
- When patients chose it themselves, 61% completed 24 weeks of treatment in a real-world follow-up[10].
The catch is the word “after.” Those results come once the induction barrier is cleared. In the real world, where many people show up still using, that barrier is the whole problem.
Why Buprenorphine and Methadone Start Easier
Here is the plain comparison:
- Buprenorphine and methadone can be started right away, often the same day you walk in, while you still have opioids on board, because they are agonists.
- Naltrexone cannot — it needs the opioid-free window first.
That single fact means buprenorphine and methadone are usually the lower-barrier choice for someone actively using heroin or fentanyl. Head to head against agonist treatment, the 2025 Cochrane review even found naltrexone may allow slightly more in-treatment opioid use[6]. Patient fit matters too: in one analysis, people experiencing homelessness actually did better on the Vivitrol shot than on buprenorphine[11].
So naltrexone is not a universal stand-in for the agonist medicines — it is the right tool for specific people, and the wrong first move for someone who cannot realistically clear the opioid-free window. None of these is “trading one addiction for another.” They are medicine. If you want to understand the option most people start with, learn how buprenorphine treatment works, or compare the two agonists head to head in Suboxone versus methadone.
Who Naltrexone Fits Best
Naltrexone is not the default first choice for everyone, but it is genuinely the best choice for several kinds of people:
- People who want nothing with any opioid activity in it. Some people are firmly done with anything that touches an opioid receptor, and that preference is legitimate. Naltrexone honors it while still being real, evidence-based treatment.
- People who have already finished detox. If you have gotten through withdrawal — through a detox program, a hospital stay, or time in custody — the hardest part is behind you and the Vivitrol shot becomes a strong option[7].
- People leaving jail, prison, or reentry programs. Time in custody means an enforced opioid-free stretch, which clears the induction hurdle automatically. A meta-analysis of 11 studies and 1,045 justice-involved people found naltrexone improved retention, reduced reincarceration, and cut opioid relapse[12]. Release is also a moment of very high overdose risk, because tolerance drops during custody, and a shot given at the gate buys a protected window.
- People whose jobs rule out opioid-based medicines. Some licensing boards and safety-sensitive roles — certain pilots, some federal jobs, some health professionals in monitoring programs — restrict agonist medications. Naltrexone may be the only option that fits those rules.
- People who also struggle with alcohol. Because naltrexone is FDA-approved for alcohol use disorder as well, it can treat both at once[4].
It is worth being just as clear about the other side. Naltrexone is generally not the first-line pick for someone still actively injecting heroin or fentanyl as an outpatient, because so many people in that situation never clear the opioid-free window[8]. For them, buprenorphine or methadone usually offers an easier start. In pregnancy, buprenorphine is typically preferred, and naltrexone should be a specialist conversation.
The Safety Point Everyone on Naltrexone Needs to Hear
There is one safety issue too often left unsaid, and it is the most important thing here after the induction warning. It is not that naltrexone is dangerous — it is what can happen if you stop.
When you are on naltrexone, your opioid tolerance drops, because you are not using. That is good, until it isn’t. If you stop the medicine and go back to opioids at a dose that used to feel normal, that dose can now kill you. The body that once handled it no longer can, and today’s supply is laced with fentanyl, which is far stronger and less forgiving.
This is documented, not a scare story. An Australian review of 74 deaths among people who had been on naltrexone for opioid dependence found that opioid toxicity caused 86.5% of them — and in many cases naltrexone was no longer detectable in the body, meaning the person had stopped taking it before the fatal overdose[13]. The danger is the gap between stopping and returning to use.
So if you or someone you love is on naltrexone:
- Keep naloxone (Narcan) in the house and know how to use it, the way you keep a smoke detector. It reverses an opioid overdose within minutes and is sold over the counter.
- Do not treat a missed shot as a green light to use. The protection fades, and that is exactly the high-risk window.
- Call SAMHSA’s National Helpline at 1-800-662-HELP (4357) any time for free, confidential help, or call or text 988 if anyone is in crisis.
The biggest reason naltrexone looks weaker than buprenorphine in studies is the starting line, not the medicine. When researchers detox everyone first, the Vivitrol shot holds up about as well as buprenorphine[9]. The gap opens when people are still using at the start, because so many never clear the opioid-free window: about 63% get started when detox is still required, versus 85% when already detoxed[7]. The obstacle is getting on it. Once people are on it and stay on it, it works.
What to Expect From Side Effects and Monitoring
Naltrexone is well tolerated by most people, but a few things are worth knowing before you start so nothing catches you off guard.
| What to expect | What it looks like | What it means |
|---|---|---|
| Liver check before starting | A simple blood test (LFTs) | Naltrexone carries a precautionary liver warning, so a baseline test is standard care[14] |
| Early nausea or headache | Most common in the first weeks, usually mild | Tends to settle; ask your provider if it lingers |
| Injection-site reaction (Vivitrol) | Soreness, swelling, or a lump where the shot goes | Usually minor, but report severe pain or a hard knot[14] |
| Low mood | Feeling down, especially early | Worth tracking — see below |
Depression deserves real attention, not because naltrexone causes it, but because untreated low mood makes people quit. In one study, 14.2% of patients had moderate or severe depression at the start of treatment[15], and people whose mood improved after the first injection were more likely to come back for the second[16]. The lesson: pairing naltrexone with counseling or mental-health support is not an extra. It is part of what makes it work.
Take the Next Step
If you have read this far, you are not looking for a reason to keep using — you are looking for the door out. Naltrexone may be that door, especially if you have already gotten through detox or are about to, and you want a medicine with no opioid in it at all. It may also turn out that buprenorphine or methadone is the easier place to start. There is no shame in either, and the only wrong move is doing nothing.
You do not have to figure this out alone or have it all worked out before you reach for help. If your story started with painkillers, it can help to understand prescription opioids as a class and how dependence takes hold. The path is more walkable than the fear makes it look: a provider, the right medicine for your situation, and a life that gets bigger from there.
Find treatment that fits your situation →
For free, confidential help any time of day or night, call SAMHSA’s National Helpline at 1-800-662-HELP (4357). If you or someone you love is in immediate danger or having thoughts of suicide, call or text 988, or call 911. Keep naloxone close.
If any of this lands, the next step doesn’t have to be a big one. You can find treatment now and get matched with someone who can help you find the right care and take the next step. Reaching out today is a real step forward — and one you can make right now.
Frequently asked questions
Is naltrexone an opioid?
No. Naltrexone is the opposite of an opioid. It is an antagonist, a blocker, that sits on the same receptors heroin, fentanyl, and prescription painkillers use and shuts them out[1]. It produces no high of its own, so there is nothing in it to get addicted to and nothing worth selling or diverting. Stopping it causes no withdrawal either, because your body does not become physically dependent on it. That is exactly why it appeals to people who want a medicine with no opioid activity in it at all, and it is a key difference from buprenorphine and methadone, which gently switch the receptors on.
What is the difference between Vivitrol and oral naltrexone?
They are the same medicine in two forms. Oral naltrexone is a tablet you take every day. Vivitrol is the extended-release injection, one shot into the muscle that keeps opioids blocked for about four weeks[4]. The difference matters because daily pills are hard to keep up: the large Cochrane review of oral naltrexone found only about 28% of people stayed in treatment, and it did not beat placebo[3]. The monthly shot removes that daily decision and roughly doubles how many people stay in treatment compared with the pill[5]. If you choose naltrexone, the Vivitrol injection is usually the better version.
Why do I have to be opioid-free before starting naltrexone?
Because naltrexone pushes opioids off their receptors, taking it while opioids are still in your system sets off precipitated withdrawal, a sudden, severe version of dope sickness that comes on faster and harder than natural withdrawal. To avoid that, you need to be genuinely off opioids first, usually 7 to 10 days, and longer for fentanyl, which clears the body more slowly. That waiting period is the real barrier, not the medicine: when people still have to detox first, about 63% get successfully started on the shot, versus 85% when they are already detoxed[7]. If you are still using, getting onto naltrexone usually means a medical detox first, which is far easier with help than alone.
Does naltrexone work as well as Suboxone or methadone?
When people get on it and stay on it, naltrexone works, it cuts opioid use compared with no medication[6], and a Norwegian study that detoxed everyone first found the Vivitrol shot held up about as well as buprenorphine-naloxone[9]. The honest difference is the starting line. Buprenorphine and methadone can be started the same day, even while you are still using, while naltrexone requires the opioid-free window first. So for someone actively using heroin or fentanyl, the agonist medicines are usually the lower-barrier choice. Naltrexone is the right tool for specific people, not a universal stand-in. You can read how buprenorphine works to compare.
Who is naltrexone best for?
It fits several people especially well: those who want nothing with any opioid activity in it; those who have already finished detox, since the hardest part is behind them; and those leaving jail or prison, where an enforced opioid-free stretch clears the induction hurdle and a monthly shot is easy to manage. The evidence in justice-involved people is solid, a meta-analysis of 1,045 people found naltrexone improved retention and cut relapse and reincarceration[12]. It also helps people whose jobs rule out opioid-based medicines. It is generally not the first pick for someone still actively injecting heroin or fentanyl, who often cannot clear the opioid-free window[7].
Is it dangerous to stop naltrexone?
Stopping the medicine itself causes no withdrawal, that part is easy. The danger is going back to opioids after you stop. While you are on naltrexone and not using, your tolerance drops, so a dose that once felt normal can be fatal if you relapse, and today’s fentanyl-laced supply makes that worse. A review of 74 deaths among people who had been on naltrexone found opioid toxicity caused 86.5% of them, and in many cases the person had already stopped taking the medicine before the fatal overdose[13]. The protection is simple: keep naloxone (Narcan) on hand, know how to use it, and if you are thinking about stopping, plan it with your provider. Free help is at SAMHSA, 1-800-662-HELP (4357).
Can naltrexone also treat alcohol addiction?
Yes. The same opioid blocker is FDA-approved for alcohol use disorder, and it comes in both the daily pill and the monthly Vivitrol shot for that use too[4]. For drinking, it works by taking some of the reward out of alcohol, which helps many people cut back or stop. That makes naltrexone a good fit for someone struggling with both opioids and alcohol, since one medicine can help with both. A provider can tell you whether it makes sense for your situation.
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