See also Warning, How to Use, and Precautions sections.
Nausea, vomiting, constipation, stomach pain, headache, dizziness, trouble sleeping, increased sweating, flushing, and dry mouth or strange taste in the mouth may occur. If any of these effects persist or worsen, tell your doctor or pharmacist promptly.
Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.
Tell your doctor right away if you have any serious side effects, including: mental/mood changes (anxiety, agitation, confusion, memory loss), uncontrolled movements (tremor), ringing in the ears, fainting, severe headache, fast/pounding/irregular heartbeat, chest pain.
Get medical help right away if you have any very serious side effects, including: eye pain/swelling/redness, widened pupils, vision changes (such as seeing rainbow around lights at night).
If you have been taking opioid medications regularly, you could have withdrawal symptoms within minutes after taking naltrexone. Tell your doctor right away if you have any of the following symptoms of opioid withdrawal: mental/mood changes (such as anxiety/irritability), fast breathing, yawning, sweating, watering eyes, goose bumps, muscle twitching.
This drug may rarely cause seizures. Get medical help right away if you have a seizure. If you have a seizure while taking bupropion, you should not take this drug again.
Naltrexone may rarely cause serious (possibly fatal) liver disease. The risk is increased when larger doses are used. Discuss the risks and benefits with your doctor. Stop using this medication and tell your doctor right away if you have symptoms of liver damage, including: persistent nausea/vomiting, loss of appetite, severe stomach/abdominal pain, yellowing eyes/skin, dark urine.
A very serious allergic reaction to this drug is rare. However, get medical help right away if you notice any symptoms of a serious allergic reaction, including: rash, itching/swelling (especially of the face/tongue/throat), painful sores in the mouth/around the eyes, severe dizziness, trouble breathing.
This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.
In the US -
Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088 or at www.fda.gov/medwatch.
In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.