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What's the difference between naltrexone and naloxone?

Medically reviewed by Carmen Pope, BPharm. Last updated on March 30, 2023.

Official answer


Naltrexone and naloxone are both drugs called opioid antagonists. That means these medications bind to opioid receptors in the brain to block the effects of other drugs. Naltrexone is used as part of treatment for opioid or alcohol use disorder. Naloxone is used only to reverse the effects of an overdose quickly.

What is naltrexone?

Naltrexone is a drug used as part of treatment for opioid use disorder. It is given as a long-acting injection prescribed to block the pleasurable (euphoric) and relaxing (sedative) effects of an opioid drug like heroin or morphine. Naltrexone is not an opioid and is not addictive. It does not cause withdrawal symptoms when stopped suddenly.

As long as the drug is taken, the effects of opioids will be blocked and cravings for opioids will be reduced. This may help a person not use opioid drugs while continuing other treatments, like counseling.

Naltrexone may also be used to treat alcohol use disorder. This drug is given as a daily pill or as a long-acting injection. Taking naltrexone daily may reduce cravings for alcohol and help a person maintain sobriety.

Drinking alcohol stimulates the brain to produce endorphins. Endorphins bind to opioid receptors and cause the pleasurable effects of alcohol. When these receptors are blocked by naltrexone, it eliminates the pleasurable effects.

What is naloxone?

Naloxone is a short-acting drug used to reverse the effects of an opioid overdose. It can be given as a nasal spray or an injection. Naloxone treatment requires immediate medical intervention to avoid serious opioid withdrawal symptoms. Naloxone can be a life-saving medication for people at risk of an opioid overdose death.

This drug should be given at the first sign of an opioid overdose. Signs of opioid overdose include:

  • Unconsciousness
  • Slow or absent breathing
  • Pinpoint pupils
  • Blue lips or nose.

Naloxone only works against opioids like heroin, fentanyl, morphine or oxycodone. It does not block the effects of drugs like alcohol, tranquilizers, cocaine or amphetamines. If you aren't sure what a person has overdosed on, you should still give Naloxone because it won't cause additional harm.

After using naloxone, long-term treatment, including medical assistance, may be needed. So stay with the person for at least 4 hours or until help arrives.

  1. U.S. Department of Health and Human Services, Substance Abuse and Mental Health Services Administration. Naltrexone. March 21, 2023. Available at: [Accessed March 30, 2023].
  2. U.S. Department of Health and Human Services, Substance Abuse and Mental Health Services. Naloxone. January 25th, 2023. Available at: [Accessed March 30, 2023].
  3. Lifesaving Naloxone. Centers for Disease Control and Prevention. Jan 25, 2023.
  4. Acquiring Naloxone. Law Enforcement Naloxone Toolkit.,the%20drug%20by%20first%20responders.

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