What it is

Naltrexone blocks the ability of opioids to eliminate pain and induce euphoria. This removes the rewarding aspects of opioid use that result in a desire for more. It is available in an extended release injectable form that is administered every 30 days and in tablet form, taken once a day by mouth.

The extended release injection has been the most effective form of naltrexone for treating addiction. It has helped to prevent relapse when combined with counseling and other supportive services.

Naltrexone is an Medication Assisted Treatment (MAT) option for people who are able to get through the initial 7–10 days of withdrawal and are highly motivated to prevent a return to drug use. Risk of overdose is high for people who try to use large amounts of opioids to override naltrexone’s blocking effects. There is also a high risk of overdose when people skip dosages or are at the end of a dosage cycle and go back to using the amount of opioids they used to tolerate.

What it does

Naltrexone is not a controlled substance and has no potential for abuse. People feel completely normal while taking it. When the pills were the only form of naltrexone available, people with a strong impulse to use simply stopped taking their pills, and the blocking effect no longer stood in the way. The extended release injection has been a much more successful treatment for opioid use disorder. Once it is administered, stopping the effects of medication is not an option until four weeks have passed. Recent studies of MAT with extended release, injectable naltrexone have consistently shown it reduces the chance of relapse and helps people remain abstinent from opioids. It also helps to reduce craving and to keep people in treatment longer.

However, if people addicted to opioids do not stop using them for 7-10 days before starting naltrexone, they risk bringing on withdrawal symptoms that can be quite severe. Naltrexone can also block the pain relieving effects of opioid medications. People with chronic pain problems, who sometimes need to take opioid medications, should keep this in mind when they consider their MAT options.

People have tried to override the blocking effect by taking large doses of opioids on top of naltrexone. This can result in fatal overdose. Overdose risk is high for people who return to opioid use after a period of treatment with naltrexone; in part, because their tolerance goes down while they are drug-free, and they cannot handle amounts they used to take.

Where do you get it?

Any qualified medical provider, doctor, nurse practitioner, or physician’s assistant can administer injections in their offices or prescribe naltrexone pills. No special training is required. Naltrexone is not a controlled substance; there is no potential for abuse or for dependence.


The extended release injectable form of naltrexone is typically the most expensive MAT option. However, the real cost to an individual varies depending on the state where the person lives, health insurance coverage, and other factors. The provider will have information about real cost and payment options.

Who it works for

Naltrexone works well for highly motivated people who are able to stop opioid use for 7-10 days prior to beginning treatment. It is a good option for those who are eager to eliminate all opioids. The injectable form is helpful for people who have a hard time keeping up with daily pills. Since it is approved for treating alcohol problems as well, people taking naltrexone may find it also helps them avoid drinking. People who need to take opioid medications for chronic pain may not be good candidates for naltrexone.

Research outcomes

The extended release injectable form naltrexone was approved for treating opioid use disorder in 2010, so a limited number of long-term studies have been completed. Results so far suggest that the extended release injection, used in combination with counseling and other supports, reduces craving and helps prevent relapse. It helps people to maintain abstinence from opioid drugs and to stay in treatment longer.

Starting naltrexone

Naltrexone treatment for opioid use disorder cannot begin until at least 7–10 days after the last opioid use, without risking immediate and severe withdrawal symptoms. It does not help with detoxification from opioids or help withdrawal symptoms. Providers often request a urine sample to make sure people are free of opioids before starting naltrexone. Some providers administer a small amount of naltrexone or a related medication to test the response. If there is no adverse reaction they will administer the full dose by injection and check periodically, to make sure it is well tolerated, before patients leave the office or treatment center.

Side effects

Most people do not have many side effects from naltrexone, but soreness in the area of the injection is very common. Other side effects can include stomach pain or nausea, diarrhea, and difficulty sleeping.


Some warnings are listed below. For complete information, see the list of websites at the end of this section.

  • High risk of overdose if people use opioids to override blocking effect.
  • Moderate to high risk of overdose due to lowered tolerance.
  • Risk of causing severe withdrawal in opioid dependent patients who have not stopped using for 7-10 days.
  • Risk of canceling pain relieving effects if opioid pain medication is given in a medical emergency.
  • Risk of depression and suicidal thoughts.
  • Risk of severe injection site reaction.

All medications can interact with alcohol, other prescription and over-the-counter medications, as well as vitamins, herbs, and supplements. If you use alcohol or other drugs in addition to opioids, your situation may be more complex. Talk to your doctor about all the medications and substances you use. To learn more about medication interactions, visit: Avoiding Drug Interactions.

Risks to others

All medications should be stored in a locked cabinet out of reach of children or pets. Excess medication should be disposed of properly. Medications should only be taken by the person they were prescribed for.

How long do I need to take it?

Deciding how long to take naltrexone is an individual choice. Like other medications used for MAT, it is safe to stay on it for long-term treatment. There is no withdrawal from naltrexone. It can be stopped at any time. However, when a long-acting injection is given, it stays in effect for a 30-day period. Some research has shown that many people return to drug use when they stop taking naltrexone, skip doses, or are at the end of a dosing cycle. When this takes place, there is a risk of increased sensitivity to the effects of opioids and a heightened risk of overdose. Generally, people need to remain in treatment a minimum of 90 days in order to benefit.


There is no research on safety of use during pregnancy or breastfeeding. It is not recommended to use naltrexone during pregnancy until there is more research about its safety.


Naltrexone is safe to use with HIV medications. There is low potential for HIV drug interactions.

Hepatitis and liver disease

People with a history of liver disease who are considering naltrexone should talk it over with their doctor. They often recommend liver function tests before treatment begins. Very large doses of naltrexone can cause liver damage, but studies show it is safe at the recommended dose, even for people with hepatitis who are taking Interferon. Talk with your doctor about your situation.


Naltrexone can keep opioid pain medications from working. It may bring on severe withdrawal symptoms in people physically dependent on opioid pain medication, unless they have stopped all opioids for at least 7-10 days beforehand. Non-opioid medications taken for pain relief can be used safely with naltrexone at all times. If you have chronic pain, and are considering naltrexone for MAT, talk with your doctor. If you use naltrexone for MAT and have to take opioid pain medication for medical reasons:

  • Inform medical staff that you are using naltrexone.
  • Stop taking naltrexone before starting to take a prescribed pain medication.
  • Do not use naltrexone while using the pain medication.
  • Restart naltrexone 7 days after the last dose of pain medication.

Legal issues

Naltrexone is not a controlled substance and legal issues are usually not a concern.

For more information

More about naltrexone

FDA approved package inserts and product labelling

The Facts about Naltrexone for Treatment of Opioid Addiction


I want to stop using opioids, but I don't want to use a medication that is an opioid. What are my options for treatment?