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Naltrexone Side Effects

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What is Naltrexone?

Naltrexone is an FDA-approved medicine used to treat alcohol and opioid use disorders.

Medication-assisted treatment (MAT) is the use of medicines in combination with counseling and behavioral therapies. It is effective in treating severe case of opioid use disorder and alcohol use disorder.2

Any practitioner licensed to prescribe Naltrexone can administer the drug. It is available in pill form for alcoholism or as an extended-release intramuscular injectable for either opioid addiction or alcoholism.

The pill form of Naltrexone is taken daily, and the extended-release injectable is taken every four weeks or once a month.1

The long-acting injectable formulation also requires a risk evaluation and mitigation strategy to ensure that the drug's benefits outweigh its risks.

Naltrexone is not a suitable MAT option for anyone younger than 18 or those with other health conditions.

How Effective is Naltrexone for Opioid & Alcohol Use Disorder?

When starting Naltrexone for opioid use disorder, patients should wait at least 7 days after their last use of short-acting opioids. They should wait 10 to 14 days for long-acting opioids. This helps reduce the risk of withdrawal symptoms.

Patients taking Naltrexone should not: 

  • Take any other opioids or illicit drugs
  • Drink alcohol
  • Take sedatives, tranquilizers, or other drugs 
  • Take the drug without first letting their practitioner know about other medications they are taking

While the oral form of Naltrexone blocks opioid receptors, only the long-acting injectable formulation is FDA approved for opioid addiction. 

Patients who stop taking Naltrexone, or relapse after a period of abstinence, may have a reduced opioid tolerance. Taking the same or lower dose of opioids used in the past can lead to life-threatening consequences. 

When beginning Naltrexone for alcohol use disorder, patients must not be physically dependent on alcohol or other substances. To avoid intense side effects like nausea and vomiting, patients usually wait until after alcohol detox before taking Naltrexone.

Naltrexone binds to the endorphin receptors in the body. It blocks the effects of alcohol. It also reduces alcohol cravings and the amount of alcohol consumed.

Once a patient stops drinking, Naltrexone use helps them maintain sobriety. Naltrexone MAT treatment continues for 3 to 4 months. 

Practitioners must continue to assess and monitor patients who stopped taking Naltrexone. 

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How Does Naltrexone Make You Feel?

Naltrexone treatment is not addictive or psychoactive. It will not produce a high. 

This is one of the reasons why it is a popular treatment option for opioid dependence and alcohol use disorders. Like vitamins and supplements, you will not feel anything when you take it.

If you stop treatment, you will not suffer any withdrawal symptoms. As Naltrexone blocks the body from responding to endorphins, you may notice more subdued effects after drinking. 

For example, after taking Naltrexone and consuming your first drink, you may not experience the typical ‘buzz.’

As you do not experience a buzz from drinking, your cravings for another drink may diminish. Many patients say Naltrexone lessens their enjoyment of drinking.

What are the Side Effects of Naltrexone?

Naltrexone may produce certain side effects. For medical advice about side effects, call your doctor for an appointment to discuss.

Common Side Effects

Common side effects you may experience include:1

  • Nausea
  • Sleepiness
  • Headache
  • Dizziness
  • Vomiting
  • Loss of appetite
  • Painful joints
  • Muscle cramps
  • Cold symptoms such as a runny or stuffy nose
  • Trouble sleeping
  • Toothache

Rare/Less Common Side Effects

Rare and less common side effects can also occur. 

Patients should call their doctor immediately if they experience any of these rare or less common side effects at the injection site:1

  • Intense pain
  • The area feels hard
  • A large area of swelling
  • Lumps
  • Blisters
  • An open wound
  • A dark scab

Long-Term Side Effects

For some users, Naltrexone may cause some long-term side effects such as:

  • Liver damage
  • Allergic pneumonia
  • Infections or skin reactions

The risk of liver damage increases with large doses of Naltrexone and in those with a history of hepatitis or liver disease.

Serious Side Effects

Serious side effects of Naltrexone can include:1

  • Overdose
  • Dark urine
  • Stomach pain
  • Yellowing of the eyes or skin
  • Suicidal thoughts

Severe side effects of Naltrexone include the risk of opioid overdose. Accidental overdose can occur in two ways.

Naltrexone blocks the effects of opioids, including heroin or opioid pain medicines. 

Patients who try to override this blocking effect by taking large doses of opioids may experience: 

  • Severe injury
  • Coma
  • Death

After taking a dose of Naltrexone, the blocking effect slowly decreases and goes away over time. People taking Naltrexone for an opioid use disorder can also become more sensitive to the effects of opioids.

Patients should speak with their doctor for medical advice about the increased sensitivity to opioids and the risk of overdose.

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Risks & Dangers of Taking Naltrexone 

As Naltrexone may make you more sensitive to smaller doses of opioids than previously used, you should not take heroin or any narcotic drugs. 

Naltrexone may increase thoughts of suicide. Speak with your health care practitioner immediately if you start to feel more depressed or have thoughts about hurting yourself after using Naltrexone. 

Report any unusual behaviors or thoughts that trouble you, especially if they are new or worsen quickly. You should also tell your doctor if you have any sudden or intense feelings like: 

  • Nervousness
  • Restlessness
  • Violence
  • Anger
  • Fear 

Be sure to follow all your doctor's orders, too, including meeting your therapist or attending support groups.

This drug may cause some people to become dizzy, drowsy, or less alert than they usually are. If you experience any of these side effects, do not drive, use machines, or do anything else that could be dangerous if you are drowsy or are not alert.3

Never share Naltrexone with anyone else, especially someone using narcotics. This drug causes withdrawal symptoms in those using narcotics. Let all medical doctors, dentists, and pharmacists you meet with know that you are taking Naltrexone.

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How Does Naltrexone Interact With Other Drugs?

Like other medicines, Naltrexone can interact with other drugs and lead to dangerous side effects. As the drug treats alcohol and opioid addiction, patients must avoid these substances.

Before starting a treatment program with Naltrexone, patients must list any medications they are using, including over-the-counter drugs and herbal remedies.

The following drugs can adversely interact with Naltrexone:

  • Narcotic drugs, like codeine and hydrocodone
  • Diarrhea medications 
  • Disulfiram 
  • Cough medication 

Patients who must undergo laboratory tests should inform doctors and laboratory personnel that they are taking Naltrexone.

Is Naltrexone Habit-Forming?

No, Naltrexone is not a habit-forming drug. It does not cause patients to become physically or psychologically dependent.4

Updated on November 16, 2021
6 sources cited
  1. Naltrexone, Substance Abuse and Mental Health Services Administration (SAMHSA), September 2020
  2. Information about Medication-Assisted Treatment (MAT), U.S. Food & Drug Administration (FDA), February 2019
  3. Naltrexone, Mayo Clinic, February 2021
  4. 5.1. Naltrexone, National Institute on Alcohol Abuse and Alcoholism (NIH) 
  5. Kosten, Thomas R, and Tony P George. “The neurobiology of opioid dependence: implications for treatment.” Science & practice perspectives vol. 1,1 : 13-20
  6. Rosenblum, Andrew et al. “Opioids and the treatment of chronic pain: controversies, current status, and future directions.” Experimental and clinical psychopharmacology vol. 16,5 : 405-16. doi:10.1037/a0013628

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