Once-A-Month Naltrexone Injection for Substance Use Disorders

Improves Long-Term Treatment Outcomes

A woman talking to a healthcare provider.

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Naltrexone injection is a medication that is used in conjunction with other methods to treat both alcohol use disorder and opioid use disorder. The medication has become one of the most effective pharmaceutical treatments for alcohol use disorder because it works to reduce the chemical effects that alcohol has on the brain, potentially leading to decreased cravings and alcohol use. It can also be effective in the treatment of opioid dependence.


Naltrexone can be prescribed for a few different uses. These include:

  • Alcohol dependence: One of only three medications approved for the treatment of alcohol dependence, naltrexone has been used for years to help people who have already stopped drinking to avoid relapse.
  • Opioid dependence: Naltrexone has also been effective in treating people who have become addicted to prescription opioids and heroin. It is being researched for treating cocaine use disorders. It works in these conditions by blocking the effect that opioids have on the brain.
  • Other uses: Naltrexone is also used off label to treat pain caused by conditions like fibromyalgia and chronic fatigue syndrome.

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Benefits of a Monthly Injection vs. Daily Pill

Naltrexone is available as both a daily pill and a monthly injection. While both medications are effective, there are some clear benefits to a long-lasting, once-a-month injection.

Daily Naltrexone Pill

For the treatment of alcohol use disorder, naltrexone was originally prescribed as a daily pill. Naltrexone in pill form—marketed as ReVia and Depade—is still widely used.

However, there is an inherent problem with the pill form of naltrexone: it has to be taken exactly as prescribed without missing a dose. For those struggling with the effects of an alcohol use disorder, compliance with taking a daily dose can be problematic. It's easy to forget to take a dose or to intentionally skip it because of physical issues or struggles with recovery.

It was also the pill form of naltrexone that was initially approved for the treatment of opioid use disorder. For this indication, the pill is not ideal because of poor treatment adherence. Because of this, there is poor evidence supporting its benefits in reducing opioid use.

Monthly Naltrexone Injection

The Food and Drug Administration approved the once-a-month naltrexone treatment—marketed as Vivitrol—for use as a treatment for alcohol dependence in 2006. This form of naltrexone could be injected once and be slowly released into the system for a month. In 2010, the FDA also approved the use of Vivitrol to treat people with opioid dependence.

Research has found that once-a-month naltrexone is effective in reducing alcohol use. For opioid use disorder, the extended-release injectable form of naltrexone is preferred because it requires only one injection each month. Research suggests that this leads to greater medication compliance.

Before Taking

Before initiating treatment with injectable naltrexone, your healthcare provider will perform a physical exam, may determine your liver function, and conduct a drug test. Because naltrexone is an opioid antagonist, taking it may lead to opioid withdrawal if you have taken an opioid medication within the last 10 days.

It is important to be opioid-free for a certain period of time before you begin receiving naltrexone injections.

Precautions and Contraindications

You should not receive monthly naltrexone injections or take other naltrexone-containing medications if you are actively using opioids. The Substance Abuse and Mental Health Services Administration (SAMHSA) says that people who are being treated with naltrexone may have a reduced tolerance to opioids after the dose goes away.

This can lead to potentially life-threatening consequences when people take opioids at the same levels they previously used. Accidental overdose can occur, which may result in death.

Because the injection medication bypasses the first-pass metabolism by the liver, the injectable form may reduce the risk of liver toxicity. However, the Food and Drug Administration (FDA) warns of the potential for liver toxicity if naltrexone is taken at levels higher than the recommended dose. Monthly naltrexone injections should not be used by people who have acute hepatitis or liver failure. 

How to Take

If you believe that you have an alcohol or opioid use disorder or want to cut back on your use, talk to your doctor about your treatment options. Your doctor will perform an evaluation of your health and needs to determine if a monthly naltrexone injection is right for you.

If your doctor determines that this approach might be appropriate, your doctor will give you an intramuscular injection in the gluteal muscles every four weeks. You may find that medication adherence is easier than taking a daily pill because it only requires one injection each month.

Side Effects

The side effects of monthly naltrexone injections are similar to those of daily oral naltrexone. Possible side effects may include:

  • Abdominal pain
  • Back pain
  • Decreased appetite
  • Dizziness
  • Fatigue
  • Headache
  • Injection site reactions
  • Joint pain
  • Muscle aches
  • Vomiting

In one large study looking at the use of naltrexone to treat alcohol use disorder, of those taking a 380 milligram dose, 14.1% dropped out of the treatment due to side effects, including nausea, headache, and fatigue. Only 6.7% of the group receiving 190 milligrams discontinued treatment due to adverse side effects.

The study was one of the largest trials of subjects treated with medication for alcohol dependence. The researchers concluded that extended-release naltrexone was well tolerated and significantly reduced heavy drinking in actively drinking individuals.

Severe side effects can also occur in some cases. These may include:

  • Allergic reactions
  • Feelings of depression
  • Liver damage
  • Reactions at the injection site (which may be severe and require intervention)
  • Suicidal thoughts or behaviors

If you are having suicidal thoughts, contact the National Suicide Prevention Lifeline at 988 for support and assistance from a trained counselor. If you or a loved one are in immediate danger, call 911.

If you are taking naltrexone to treat alcohol use disorder or opioid use disorder, you should seek medical attention immediately if you begin to experience signs of a serious allergic reaction, including trouble breathing, difficulty swallowing, or swelling of your mouth, face, or hands.


Research suggests that naltrexone can be effective in the treatment of both alcohol use disorder and opioid use disorder.

Naltrexone to Treat Alcohol Use Disorder

One study indicated that the injection of a 380 mg dose of naltrexone resulted in a 25% reduction of heavy drinking days, while a 190 mg dose reduced heavy drinking days 17%.

Research suggests that men may respond to naltrexone treatment more than women and that those who begin treatment after a period of drug or alcohol abstinence may experience greater treatment effects.

Studies also indicate that people who are given Vivitrol injection get variable blood levels and those who get higher blood levels experience fewer cravings.

The long-acting form of naltrexone may improve treatment strategies for people with alcohol dependence by eliminating the medication compliance issue.

Naltrexone to Treat Opioid Use Disorder

One study looking at the effectiveness of monthly naltrexone for the treatment of opioid use disorder found that the medication significantly improved abstinence from opioids. Participants treated with a monthly naltrexone injection were abstinent in 90% of the weeks during the study, on average, compared to only 35% abstinence in the placebo group.

In addition to improved abstinence, those in the naltrexone group also reported decreased drug cravings and had fewer drug relapses. 

If you or a loved one are struggling with substance use or addiction, contact the Substance Abuse and Mental Health Services Administration (SAMHSA) National Helpline at 1-800-662-4357 for information on support and treatment facilities in your area.

For more mental health resources, see our National Helpline Database.

12 Sources
Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Buddy T
Buddy T is an anonymous writer and founding member of the Online Al-Anon Outreach Committee with decades of experience writing about alcoholism.