Get emergency medical help if you have signs of an allergic reaction to naltrexone: hives; chest pain, wheezing, difficult breathing; feeling light-headed; swelling of your face, lips, tongue, or throat.
Using opioid medicine while you are receiving this medicine could stimulate opioid withdrawal symptoms. Common withdrawal symptoms are yawning, sweating, fever, stomach pain, vomiting, diarrhea, watery eyes, runny nose, goose bumps, body aches, shaking, muscle twitching, trouble sleeping, and feeling restless or anxious.
Call your doctor at once if you have:
weak or shallow breathing;
new or worsening cough, wheezing, trouble breathing;
severe pain, swelling, blistering, skin changes, a dark scab, or a hard lump where the medicine was injected;
liver problems - stomach pain (upper right side), dark urine, tiredness, jaundice (yellowing of the skin or eyes); or
symptoms of depression - unusual mood or behavior changes, loss of interest in things you once enjoyed, crying, new sleep problems, thoughts about hurting yourself.
You may feel nauseated the first time you receive this medicine. You may also have a headache, tiredness, joint and muscle pain, loss of appetite, and vomiting.
Common naltrexone side effects may include:
nausea, vomiting, loss of appetite;
joint pain, muscle cramps;
dizziness, drowsiness;
sleep problems (insomnia);
tooth pain; or
cold symptoms such as stuffy nose, sneezing, sore throat.
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
 Naltrexone side effects (more detail)
