Naltrexone and Vivitrol, Explained

Key takeaway

Naltrexone blocks opioid receptors. The daily pill is used for alcohol use disorder. Vivitrol is the monthly shot a clinician gives. The FDA says starting it too soon after opioid use can cause severe withdrawal, and that overdose risk rises if opioids are used during or after treatment. Do not start it at home.

Last updated: Mon Oct 05 2026 00:00:00 GMT+0000 (Coordinated Universal Time)

You have heard that a shot can block opioids, and you are trying to figure out whether you can start it the morning after you use. You cannot. Naltrexone is not an opioid. It blocks opioid receptors. SAMHSA says it blocks the euphoric and sedative effects of opioids such as heroin, morphine, and codeine, and that it reduces and suppresses opioid craving. The same medicine is used in alcohol treatment, where SAMHSA says it blocks the effects and feelings of alcohol, reduces craving, and reduces the amount people drink. Vivitrol is the brand name of the extended-release injection. The FDA says a health care provider must prepare and give that injection. What follows is the two forms, the two conditions, and the overdose risk if you start too soon or use opioids around the blockade. It does not give a dose, a home induction, or a way to inject it yourself.

If breathing is slow or the person will not wake, call 911 and use naloxone if you have it. How to respond is the overdose guide. For a mental health crisis, including suicidal thoughts, call or text 988. The FDA says patients on Vivitrol should be monitored for depression or suicidal thinking.

Two forms, and they are not approved for the same job

SAMHSA says any practitioner licensed to prescribe can prescribe naltrexone. The pill is taken daily and is described for alcohol use disorder. The extended-release injection is given every four weeks, or once a month, by a practitioner, and is approved for alcohol use disorder and for opioid use disorder. SAMHSA is explicit that the pill also blocks opioid receptors, and that only the long-acting injection is FDA-approved as a medication for opioid use disorder. Do not treat a tablet bottle as if it were the monthly shot. The FDA label says Vivitrol must be prepared and administered by a health care provider, as a deep muscle injection. It is not a shot you mix at home.

NIDA says any clinician with prescribing authority can prescribe naltrexone, and that when people stay on it, it can work as well as buprenorphine at preventing a return to opioid use. Starting it is harder, because other opioids usually have to stop first. How it compares with methadone and buprenorphine is the medication FAQ. Those other doors are the methadone guide and the Suboxone guide. The medicine in front of you is the blocker.

SAMHSA says naltrexone is one part of a comprehensive plan that includes counseling and other therapies. The FDA says the same thing in its own words: treatment should be part of a comprehensive management program that includes psychosocial support. The medicine alone is not the whole treatment. SAMHSA also says it is not a recommended option for anyone younger than 18, or for patients with certain other health conditions that a practitioner has to sort out. The FDA label says safety and efficacy of Vivitrol have not been established in children.

Alcohol, after withdrawal is already treated

The FDA indication for alcohol dependence is narrow at the start. Vivitrol is for patients who have been able to abstain from alcohol in an outpatient setting before treatment begins. Patients should not be actively drinking when the first injection is given. Section 5.10 of the label says use of Vivitrol does not eliminate or diminish alcohol withdrawal symptoms. NIAAA's consumer handout makes the same point for the alcohol medicines as a group: naltrexone, acamprosate, and disulfiram do not help withdrawal symptoms. Withdrawal medicines are a different decision, made by a clinician.

SAMHSA says that when naltrexone is started for alcohol use disorder, the person must not be physically dependent on alcohol or other substances. Practitioners typically wait until after detox, to avoid strong side effects such as nausea and vomiting. Once drinking has stopped, SAMHSA says naltrexone can help people maintain that stop, and that it reduces craving and the amount consumed. How long you stay on it is the prescriber's decision. Do not pick a stop date from a leftover vial, and do not start a second month from one either.

Tell the prescriber about liver or kidney disease, bleeding problems, pregnancy, and every other medicine. The FDA label describes hepatitis with Vivitrol and says to stop it if signs of acute hepatitis appear. Ongoing stomach pain, dark urine, or yellowing of the eyes are reasons to call the prescriber. A blood test still belongs in a clinic.

Opioids: do not start this after recent use on your own

The FDA indication for opioid dependence is prevention of relapse after opioid detoxification. It is not a medicine for withdrawal itself. Vivitrol is contraindicated in people with current physiologic opioid dependence, people in acute opioid withdrawal, and people receiving opioid analgesics. That includes people being treated for alcohol dependence who also use opioids. The label says they should tell the prescriber about any recent opioid use, including tramadol.

The opioid-free interval in the label is a minimum of 7 to 10 days, to avoid precipitated withdrawal that may be severe enough to require hospitalization. People transitioning from buprenorphine or methadone may be vulnerable for as long as two weeks. Review of cases after the drug was marketed found withdrawal severe enough for hospital admission and, in some cases, intensive care. There is no completely reliable way for a patient to know the wait was long enough. A negative drug screen or a naloxone challenge does not erase the risk, especially when someone is leaving buprenorphine. If a faster switch is appropriate, the FDA says it belongs in a medical setting where precipitated withdrawal can be managed. Faster does not mean unsupervised.

SAMHSA says not to start naltrexone if you currently use opioids, are physically dependent, or are in withdrawal. Symptoms it lists include anxiety, sleeplessness, sweating, muscle aches, and stomach cramps. Feeling mostly okay is not a clearance. Do not swallow a tablet or seek an injection to see what happens.

Patients on naltrexone should tell the practitioner about every medicine. Opioid cough, cold, diarrhea, and pain products can be blocked or can interact with the start. SAMHSA also says patients taking naltrexone should not use other opioids or illicit drugs, and should not add sedatives or tranquilizers. Pain care is harder while the blockade is in place. NIDA says clinicians may advise stopping naltrexone before surgery if opioid pain medicine is likely afterward. Do not stop the injection the night before an operation without the prescriber.

The overdose risk is why the timing matters

SAMHSA and the FDA describe the same trap.

Naltrexone blocks opioids. Trying to overcome that block by taking large amounts can cause serious injury, coma, or death. After a dose, the block fades. At the end of the month, after a missed injection, or after the medicine is stopped, tolerance is lower than it was before treatment. An amount you used in the past, or a smaller amount, can be fatal. SAMHSA says people who discontinue naltrexone or return to use after abstinence may have a reduced tolerance, so the same or even lower doses of opioids can be life-threatening. Tell family what that sensitivity means. The FDA says clinicians should strongly consider recommending or prescribing naloxone or nalmefene at the first injection and at each one after, because a return to opioid use is still possible.

Naltrexone is not addictive, and SAMHSA says stopping it does not cause withdrawal symptoms. That sentence is about the medicine itself. It is not permission to stop and then use. Keep naloxone where someone else can reach it. You cannot give it to yourself if you have stopped breathing.

Serious injection-site reactions can occur, including intense pain, swelling, lumps, open wounds, and tissue injury that has required surgery. SAMHSA lists those, along with allergic reactions such as rash, swelling of the face or tongue, wheezing, chest pain, and feeling faint. Trouble breathing, swelling of the face or throat, or chest pain needs emergency help. Call the prescriber for a worsening injection site. Do not inject a corrective dose yourself.

Programs can be located on FindTreatment.gov. SAMHSA's National Helpline is 1-800-662-HELP (4357). Call or text (800) 653-9376 if you need help finding a prescriber who can talk through naltrexone after a real opioid-free assessment.

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Common Questions

What is the difference between naltrexone pills and Vivitrol?

Both contain naltrexone, which blocks opioid receptors. SAMHSA says the pill can be taken daily for alcohol use disorder, and that the extended-release injection is given about once a month by a practitioner for alcohol use disorder and for opioid use disorder. SAMHSA also says that while the pill blocks opioid receptors, only the long-acting injection is FDA-approved as a medicine for opioid use disorder. Vivitrol is that injection. A clinician prepares and gives it. It is not a shot you mix at home.

Can I take the first dose the day after I use opioids?

No. The FDA says patients should be opioid-free before Vivitrol, including people being treated for alcohol dependence, because starting too soon can precipitate withdrawal severe enough to need a hospital. It recommends a minimum of 7 to 10 days off short-acting opioids. People leaving buprenorphine or methadone may be vulnerable for as long as two weeks. SAMHSA's wait is in the same range: at least 7 days after short-acting opioids and 10 to 14 days after long-acting ones. A clinician manages that gap. Do not test a dose alone.

Will naltrexone stop alcohol withdrawal?

No. The FDA label says Vivitrol does not eliminate or diminish alcohol withdrawal symptoms. Patients should not be actively drinking when the first injection is given, and the alcohol indication is for people who have been able to abstain in outpatient care before they start. SAMHSA says practitioners usually wait until after alcohol detox, because starting sooner can bring nausea and vomiting. Withdrawal care is a different medicine, chosen by a clinician.

Why is overdose a risk if the medicine blocks opioids?

Two ways, in both the FDA label and SAMHSA's description. Trying to overcome the blockade with large amounts of opioids can cause serious injury, coma, or death. Tolerance also falls. At the end of a dosing interval, after a missed dose, or after the medicine is stopped, an opioid amount that used to be familiar, or a smaller amount, can be fatal. The FDA says to strongly consider naloxone or nalmefene for that emergency. Call 911. Do not try to break through the block.

Is naltrexone addictive?

SAMHSA says naltrexone is not an opioid, is not addictive, and does not cause withdrawal symptoms when it is stopped. Stopping it is still dangerous if you then use opioids, because tolerance is lower. NIDA says it blocks opioid receptors so opioids cannot produce pleasure, and that evidence suggests it reduces opioid craving. It is also approved for alcohol use disorder. It is one part of a plan that includes counseling. It is not a cure, and it is not a dose you set yourself.