Naltrexone: Uses, Side Effects and Dosage

Last Updated: November 27, 2023

Editorial Policy | Research Policy

Naltrexone may be helpful for treating opioid or alcohol addiction, but it’s important to be aware of the different side effects that can result from this medication.

Naltrexone is a prescription medication that is chemically similar to naloxone. Both of these medications work to block opioid receptors in the brain, but each drug is used for different situations. Naloxone works as an opioid reversal drug that can stop an overdose, while naltrexone is used to help treat alcohol and opioid use disorders. 

If you or someone you love is struggling with opioid abuse and addiction, professional treatment that includes medications like naltrexone can help you find lasting recovery.

What Is Naltrexone?

Naltrexone is a prescription medication that is FDA-approved to treat alcohol use disorder (AUD) and opioid use disorder (OUD). Naltrexone binds to opioid receptors in the brain and blocks the euphoric feelings associated with alcohol or opioid use. The medication can also help to curb cravings. 

Dextro-Naltrexone vs. Levo-Naltrexone

Naltrexone’s chemical structure has “right” (dextro) and “left” (levo) mirror structures called enantiomers. Commercially available naltrexone is the levo (or “left”) enantiomer of naltrexone and is an opioid antagonist. This means that it essentially blocks the effects of opioids. 

Conversely, the dextro (or “right”) enantiomer has not been found to contain properties that would be helpful for alcohol or opioid addiction treatment. As a result, this version of naltrexone is not commercially available. 

Is Naltrexone a Controlled Substance?

Naltrexone is not a controlled substance. It does not cause addiction to develop, and it will not lead to withdrawal symptoms if someone abruptly stops using the medication.

Naltrexone Brand Names

Naltrexone is available as film-coated tablets under the brand name ReVia or as an injectable suspension called Vivitrol. Generic tablets are also available. 

Naltrexone Uses

Naltrexone works to block the euphoric effects of opioids and reduce cravings for alcohol and opioids. As a result, naltrexone is FDA-approved for treating opioid and alcohol addiction. Other uses for naltrexone are known as off-label uses and are not FDA-approved.

Naltrexone for Alcohol Use Disorder and Opioid Addiction

Naltrexone can be helpful for patients who have not used a short-acting opioid for at least seven days or a long-acting opioid for at least 10 to 14 days. Naltrexone can help reduce opioid cravings after the detox process is complete, but it is important to abstain from opioids while taking this medication. In the case of a relapse, it is important to know that your tolerance may have changed, creating a higher risk of overdose. 

Naltrexone can also be helpful for reducing alcohol cravings. Once you stop drinking, taking naltrexone can be a tool used to help maintain sobriety. For AUD treatment, naltrexone is typically taken for three or four months, but this can vary based on your specific situation. 

Naltrexone and Bupropion (Contrave) for Weight Loss

A combination pill containing naltrexone and bupropion is available by prescription only. This tablet is used for weight loss in overweight adults who have a weight-related comorbidity, such as diabetes. The medication is marketed under the brand name Contrave. The naltrexone in the drug works to reduce cravings, while bupropion works as a norepinephrine and dopamine reuptake inhibitor. 

While this medication has been shown to be effective for weight loss, it is not without its own risks. Bupropion can cause depression, high blood pressure and a higher risk of seizures. If someone takes opioids, naltrexone can cause sudden opioid withdrawal or overuse.

Low Dose Naltrexone 

Naltrexone is commercially available as 50 mg capsules, and the total daily dose for OUD treatment is 50 mg to 100 mg. Low-dose naltrexone (LDN) refers to doses that are much smaller, typically around 4.5 mg. 

Some hypothesize that low doses of naltrexone may have pain-relieving or anti-inflammatory properties that are not seen at higher doses. There are no large-scale human studies to evaluate this, and these uses (and LDN itself) are not FDA-approved. 

How Does Naltrexone Work?

Naltrexone and its metabolites work by binding to mu-opioid receptors in the brain to oppose the euphoric effects of opioids and alcohol. Naltrexone also antagonizes, or blocks, activity at two other brain receptors that are responsible for some of the effects of opioids and alcohol (kappa and delta receptors). By doing this, naltrexone can decrease the positive feelings associated with opioid or alcohol use and result in reduced overall use. 

How Long Does It Take for Naltrexone to Work?

Naltrexone is most often taken by mouth as a capsule. Naltrexone can antagonize (or block) opioids in as little as 15 to 30 minutes after taking a dose. The time it takes for naltrexone to decrease cravings can vary from person to person. For some, cravings decrease in the first week after starting naltrexone and further decrease in subsequent weeks. 

When combined with diet and exercise, the weight loss effects of Contrave (naltrexone/bupropion) can be seen in as little as four weeks.

If you are interested in starting low-dose naltrexone (LDN) for pain management, make sure to speak with your health care provider. There are limited studies for this off-label use, and it should be managed on a case-by-case basis. 

Naltrexone Side Effects

While naltrexone is generally well-tolerated, there is always the potential for unwanted side effects. Always speak with your health care provider if you notice unwanted side effects or allergic reactions from this medication. These may include

  • Anxiety 
  • Depression 
  • Dizziness
  • Drowsiness
  • Headaches
  • Joint stiffness
  • Muscle cramps or rigidity
  • Nausea
  • Panic attack
  • Shortness of breath
  • Sleep problems
  • Twitching 
  • Weight gain 

How Long Do Naltrexone Side Effects Last?

Most often, mild side effects of naltrexone subside a few days after taking the medication. Typically, this can include side effects like sleep problems and muscle cramping. 

Naltrexone Dosage

Naltrexone can be used to treat a variety of conditions. As a result, the dose can differ based on why you are taking this medication.

Naltrexone Dose for Alcohol Use Disorder

Naltrexone for AUD should be initiated as 50 mg once daily. While the optimal recommended duration of therapy has not been established, studies have demonstrated safety when used for up to 12 weeks.

Naltrexone Dose for Opioid Dependence

When used for OUD, naltrexone can be taken as 50 mg once daily. However, there are also many other flexible dosing strategies. These typically include taking higher doses of naltrexone less often — for example, every other day or a few times per week. This can help some patients remember to take their medication. If this sounds like something that might help you, speak with your health care provider to talk about the risks and benefits of this strategy. 

Naltrexone Dose for Weight Loss

Naltrexone/bupropion for weight loss (Contrave) starts as a lower dose and slowly increases each week. In the first week, Contrave is dosed as one tablet daily. In the second week, one tablet is taken twice daily (morning and night). In the third week, two tablets are taken in the morning and one at night. In the fourth week and thereafter, two tablets are taken twice daily. 

Naltrexone Half-Life

The half-life of naltrexone, or the time it takes for half of one dose to be metabolized in the body, is between four and 13 hours. The half-life for Vivitrol, the extended-release naltrexone injection, is five to 10 days. Typically, it takes up to five half-lives for all traces of a medication to be removed from the body.

Naltrexone Overdose

There are some concerns about using naltrexone in patients with hepatitis or liver failure. However, in one case report, a patient took approximately 1500 mg of naltrexone and was hospitalized but experienced only stomach irritation. 

Naltrexone is most often slowly increased over time. Never take more than prescribed without first talking with your health care provider. In many instances, doses are increased on a case-by-case basis.

What To Avoid When Taking Naltrexone

Knowing the half-life of naltrexone is important because if the medication is taken with opioids, there is a risk of sudden withdrawal and overdose. There have been instances where naltrexone “wears off” before an opioid. Additionally, the amount of opioid needed to feel the same effect may have changed due to tolerance or taking naltrexone. Either of these reasons can put you or a loved one at higher risk for overdose. 

It is important to always tell your health care provider about any other medications you are taking. Medications that can harm the liver or cause sedation are typically used cautiously with naltrexone.

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Naltrexone Withdrawal

You are unlikely to experience withdrawal from naltrexone. However, if taken with opioids, naltrexone can cause opioid withdrawal. This medication is chemically similar to the opioid reversal naloxone, and it similarly blocks mu-opioid receptors in the brain. This means that if you took an opioid and naltrexone together, naltrexone would block the opioid and cause withdrawal to occur. It is important to start naltrexone at least seven to 10 days after your last opioid dose to minimize the risk of causing withdrawal in this way.

There is a common misconception that naltrexone is an opioid. Rather, naltrexone is a non-controlled medication, and taking this medication cannot cause dependence on it. However, opioid withdrawal symptoms and naltrexone side effects can be similar. When first starting this medication, you may experience cramping, diarrhea or other GI-related symptoms, but they should go away within the first few days. 

Find Addiction Treatment Programs in New Jersey

Located in Cherry Hill, New Jersey, The Recovery Village Cherry Hill at Cooper offers a variety of treatment option. In addition to medical detoxinpatientoutpatient and teletherapy programs, we also provide treatment for co-occurring disorders like depression. 

If you or someone you love is struggling with alcohol or opioid addiction, our experts are here to help. Contact us today to learn more about treatment programs that can work well for your situation. 


Substance Abuse and Mental Health Services Administration. “Naltrexone.” April 21, 2022. Accessed May 19, 2022. “Naltrexone Monograph for Professionals.” July 19, 2021. Accessed May 19, 2022.

Younger, J., et al. “The use of low-dose naltrexone (LDN) as […]nt for chronic pain.” Clinical Rheumatology, February 15, 2014. Accessed May 19, 2022.

Early, J., Whitten, J.S. “Naltrexone/Bupropion (Contrave) for Weight Loss.” American Family Physician, April 15, 2015. Accessed May 19, 2022.

Singh, D., Saadabadi, A. “Naltrexone.” StatPearls, May 2, 2022. Accessed May 19, 2022.

GoodRx. “Contrave (naltrexone / bupropion).” June 17, 2021. Accessed May 19, 2022.

Reece, A.S. “Clinical safety of 1500 mg oral naltrexone overdose.” BMJ Case Reports, 2010. Accessed May 19, 2022.

Medical Disclaimer: The Recovery Village aims to improve the quality of life for people struggling with a substance use or mental health disorder with fact-based content about the nature of behavioral health conditions, treatment options and their related outcomes. We publish material that is researched, cited, edited and reviewed by licensed medical professionals. The information we provide is not intended to be a substitute for professional medical advice, diagnosis or treatment. It should not be used in place of the advice of your physician or other qualified healthcare provider.

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