Naltrexone is generally well tolerated, but like all medications, it has the potential to cause side effects. The frequency of serious side effects is very low. The most common side effects are gastrointestinal, including upset stomach, nausea, vomiting, and diarrhea. The frequency of side effects is below:

• nausea (10%)
• headache (7%)
• dizziness (4%)
• nervousness (4%)
• fatigue (4%)
• insomnia (3%)
• vomiting (3%)
• anxiety (2%)
• somnolence (2%)

Most likely, you won’t have any side effects, but if you do, they usually go away with continued use. There are a few things that can be done, if a side effect persists:

1. Lower the dose. This will give the body time to adjust to the new medication. Once you feel comfortable, you can try increasing it back to a more therapeutic dose.
2. Divide the dose. Instead of taking 50 mg once daily, you could take 25 mg twice daily.
3. Take with food.
4. Combine the naltrexone with an over-the-counter medication that addresses the side effect. Usually this means taking Pepto-Bismol.

It is in Pregnancy Category C, which officially means, “Animal reproduction studies have shown an adverse effect on the fetus and there are no adequate and well-controlled studies in humans, but potential benefits may warrant use of the drug in pregnant women despite potential risks.”

For obvious reasons, it is not easy to design a conclusive study that involves giving pregnant woman various medications.