Naltrexone Side Effects

Common Side Effects

The most commonly reported side effects of naltrexone include:

• Nausea — the most common side effect, typically occurring in the first few days to weeks and often resolving on its own
• Fatigue or drowsiness
• Headache
• Decreased appetite
• Stomach discomfort or cramping
• Dizziness
• Sleep disturbances

Many people find that side effects are mild and resolve within the first one to two weeks. Taking naltrexone with food may help reduce nausea.

Less Common but Serious Side Effects

• Liver toxicity — naltrexone can cause liver damage at high doses; standard doses (50mg) are generally considered safe for people with normal liver function, but liver function should be monitored
• Opioid withdrawal — naltrexone will precipitate withdrawal in people who are opioid-dependent; do not take naltrexone if you have used opioids recently
• Mood changes — some people report changes in mood, including depression or anxiety, particularly in the early weeks

When to Contact a Clinician

Contact your clinician if you experience:

• Severe nausea or vomiting
• Abdominal pain, especially in the upper right area
• Yellowing of the skin or eyes (jaundice)
• Dark urine
• Significant mood changes or depression
• Signs of opioid withdrawal