Stomach upset/pain, nausea, vomiting, diarrhea, constipation, loss of appetite, headache, dizziness, trouble sleeping, fever, sweating, or a 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 immediately if any of these unlikely but serious side effects occur: mental/mood changes (e.g., depression, anxiety), unusual weakness.Tell your doctor immediately if any of these rare but very serious side effects occur: vision changes, change in the amount of urine, unusual bleeding/bruising, dark urine, yellowing eyes/skin, severe stomach/abdominal pain, persistent nausea/vomiting.A very serious allergic reaction to this drug is rare. However, seek immediate medical attention if you notice any of the following symptoms of a serious allergic reaction: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing.Atovaquone can commonly cause a mild rash that is usually not serious. However, you may not be able to tell it apart from a rare rash that could be a sign of a severe allergic reaction. Therefore, seek immediate medical attention if you develop any rash.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.In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.