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Naltrexone: 7 things you should know

Medically reviewed by Carmen Pope, BPharm. Last updated on July 25, 2023.

1. How it works

  • Naltrexone may be used to treat opioid addiction or dependence or alcohol addiction.
  • Naltrexone reversibly binds to the mu opioid receptor which blocks the effects of opioids (also called narcotics). Examples of opioids include morphine, heroin, and codeine.
  • How naltrexone works in alcoholism is not completely understood; however, some experts believe it works by blocking the effects of naturally occurring opioids (such as endorphins).
  • Do not confuse naltrexone with naloxone (Narcan), which strips the opioid from the opioid receptor and is used for the emergency treatment of opioid overdose.
  • Naltrexone belongs to a class of medicines called opioid antagonists.

2. Upsides

  • When used to treat opioid (narcotic) addiction or dependence, naltrexone blocks the euphoric effects (feelings of well-being) of opioids, so the user gains no psychological benefit from the opioid. It also helps to reduce cravings. Naltrexone will precipitate withdrawal symptoms in people physically dependent on opioids.
  • Naltrexone is also used in the treatment of alcohol addiction and has also been shown to improve abstention rates, reduce the number of drinking days, and reduce the risk of relapse. It also reduces alcohol cravings.
  • Naltrexone itself does not cause physical or psychological dependence and is not considered a drug of abuse. Tolerance to naltrexone's effect does not appear to occur.
  • Apart from its opioid-blocking effects and some pupillary constriction (a decrease in the size of the pupil of the eye), naltrexon has few, if any, other reported effects.
  • Naltrexone is available in combination with morphine to prevent the misuse of morphine. Naltrexone blocks feelings of well-being that can contribute to the abuse of morphine.
  • Naltrexone is available as oral tablets and an extended-release IM injectable preparation.
  • Generic naltrexone is available.

3. Downsides

If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:

  • Nausea, headaches, depression, fatigue, insomnia, anxiety, and sleepiness are the most common side effects reported. Generally, naltrexone is well-tolerated in people who are genuinely opioid-free.
  • Naltrexone is not aversive therapy and does not cause any specific reactions when combined with opioids or alcohol; however, it may precipitate withdrawal symptoms when used with opioids, and these may be severe enough to warrant hospitalization. The use of naltrexone does not diminish or eliminate opioid withdrawal symptoms. A naltrexone challenge test may need to be performed if there is any suspicion of opioid dependence.
  • People who are dependent on opiate drugs should stop taking the opioid seven to ten days before starting naltrexone. Treatment with naltrexone should not be attempted otherwise.
  • Avoid in people currently using opioids, with certain types of liver disease, or with chronic pain who rely on opioid painkillers.
  • May not be suitable for people with kidney disease, liver disease, receiving or dependent on opioid analgesics. May cause hepatitis or significant liver dysfunction.
  • Requires good compliance to be effective. May increase vulnerability to opioids once the detoxification process is complete, which means a lower dose of opioids may cause life-threatening intoxication.
  • Does not affect the use of cocaine or other non-opioid drugs of abuse.
  • Naltrexone should only be given as part of a well-managed addiction treatment plan.
  • Only use during pregnancy if the benefits outweigh the risks. Animal studies have shown an adverse effect on the fetus but there are no adequate and well-controlled studies in humans. Excreted into breastmilk; either discontinue the drug or discontinue breastfeeding.

Note: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. View complete list of side effects

4. Bottom Line

Naltrexone is used as an adjunct to social and psychotherapy in the treatment of opioid and alcohol addiction. People taking naltrexone need to have completely stopped taking all types of opioids seven to ten days before starting naltrexone.

5. Tips

  • Take naltrexone exactly as directed by your doctor. Do not take more or less than recommended. An overdose of naltrexone has been associated with liver injury.
  • Naltrexone should be used in addition to comprehensive social and psychotherapeutic measures to reduce opioid or alcohol addiction.
  • Always carry identification that alerts medical personnel to the fact you are taking naltrexone. A naltrexone medication card is available from most treatment centers for this purpose.
  • If you try and self-administer opioids while taking naltrexone, you will not perceive any effect.
  • If you attempt to overcome the naltrexone blockade with large doses of opioids, you may die or suffer serious injury, including coma.
  • Stop naltrexone and see your doctor immediately if you develop abdominal pain lasting more than a few days, white bowel movements, dark urine, or yellowing of your eyes.
  • Talk to your doctor or pharmacist before self-administering any cough or cold remedies or pain-relieving treatments because some of these may contain codeine or other opioid-like ingredients that may interact with naltrexone.
  • Naltrexone may affect your ability to drive or operate machinery. Do not perform any kind of hazardous task if naltrexone affects you like this.
  • Tell your doctor if you are breastfeeding, pregnant, or intending to become pregnant because naltrexone may not be suitable for you.

6. Response and effectiveness

  • Peak plasma levels of naltrexone and its active metabolite occur within an hour of oral administration. The duration of naltrexone's effect depends on the dosage of naltrexone. Studies have shown that 50mg of naltrexone will block the effects of 25mg of heroin administered intravenously for up to 24 hours; doubling the naltrexone dose extends the blockade to 48 hours.

7. Interactions

Medicines that interact with naltrexone may either decrease its effect, affect how long it works, increase side effects, or have less of an effect when taken with naltrexone. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.

Common medications that may interact with naltrexone include:

  • disulfiram, used in the management of alcohol abuse
  • all medications that have sedation as a side effect, including antidepressants, first-generation antihistamines, antipsychotics, anti-anxiety medications
  • any medication that also contains an opioid, such as codeine, hydrocodone, loperamide, methadone, morphine, or oxycodone. This includes pain relievers, anti-diarrheal medications, or cough and cold preparations.

Avoid drinking alcohol or taking illegal or recreational drugs while taking naltrexone.

Note that this list is not all-inclusive and includes only common medications that may interact with naltrexone. You should refer to the prescribing information for naltrexone for a complete list of interactions.


Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use naltrexone only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Copyright 1996-2023 Revision date: July 25, 2023.