Medication-assisted treatment (MAT) is a proven program that combines drugs — like naltrexone and buprenorphine — with behavioral therapy to treat opioid use disorder. At Confidant Health, we combine evidence-based interventions such as MAT with digital resources to make healthcare more accessible.

Studies show that MAT can help 75% to 85% of users abstain from opioids. However, like most treatments, it is not free from side effects, and 46% of MAT users report quitting their program due to adverse effects.

Naltrexone is the safest FDA-approved treatment for OUD, with a discontinuation rate of 15 %. With that being said, naltrexone users can also experience side effects. In this article, we break down naltrexone's side effects and how long they take to go away.

What is Naltrexone, and How Does it Act?

Naltrexone is an FDA-approved treatment for alcohol use disorder (AUD) and opioid use disorder (OUD). It works as an opioid antagonist that occupies opioid receptors in the brain. This blocks the sedative and euphoric effects of alcohol and opioids.

Naltrexone Side Effects: A Comprehensive Overview


What Are Low-Dose Naltrexone Side Effects?

Low-dose naltrexone (1-5 mg/day) has fewer side effects than regular-dose naltrexone. On top of that, no serious side effects have been reported. 

Studies show vivid dreams — affecting 37% of users — and headaches are the most common side effects of low-dose naltrexone. In addition, 6% of patients also report difficulty sleeping. 

How Long Do Naltrexone Side Effects Last?

Half-life refers to the time in which the concentration of any drug in the blood reduces by half. The body generally eliminates 97% of a medication after a duration of 5 half-lives.

Naltrexone's half-life varies depending on its formulation. The half-life of the pill form is between 4-6 hours, meaning the body takes 20-30 hours to eliminate it.

In contrast, the half-life of the depot injection, a formulation which releases slowly over time, is 5-10 days. This means it can remain in the system for 25-50 days.

Thus, naltrexone's side effects can last from a few days to weeks (depending on the dose and the route of administration). Some patients may experience side effects for longer if they:

What to Do if You Develop Naltrexone Side Effects

Most side effects of naltrexone go away on their own within a few weeks. However, some users may experience more serious (or permanent) side effects that need immediate medical attention. 

Users should promptly seek medical help if they experience:

Serious side effects:

  • Depression

  • Suicidal thoughts

  • Injection site reactions

  • Allergic reactions (swelling of the face, lips, or tongue; skin rash; difficulty breathing)

  • Abdominal pain lasting more than a few days

  • Liver damage (evident from the yellowing of the eyes)

Side effects that won't go away:

  • Tiredness

  • Nausea

  • Sleepiness

  • Headache

  • Dizziness

  • Vomiting

  • Decreased appetite

  • Painful joints

  • Muscle cramps

  • Flu-like symptoms

  • Insomnia

  • Toothache

Frequently Asked Questions (FAQs)

Does Naltrexone Make You Feel High? 

No. Naltrexone is an opioid antagonist. This means it blocks opioid receptors without stimulating them. In other words, it cannot make users feel 'high.'

Does Naltrexone Make You Sleepy? 

Possibly. Multiple studies show naltrexone can cause drowsiness and sleepiness.

Does Naltrexone Make You Sick?  

Naltrexone is well-tolerated. However, some users may feel nauseous when using the medication.

Does Naltrexone Make You Tired?

This is uncommon. Nevertheless, up to 20% of users may experience malaise, fatigue, lethargy, and sluggishness when using the drug.

Get Naltrexone at Confidant Health!

With our state-of-the-art virtual services, access to medication-assisted treatment has never been easier.

Get in touch with us today, and take the first step on your path to recovery.