See also Warning section. Upset stomach, unusual tiredness, constipation, diarrhea, dizziness, lightheadedness, drowsiness, loss of appetite, or headache may occur. If any of these effects persist or worsen, tell your doctor or pharmacist promptly. If your doctor has directed you to use this medication, remember that 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: fainting, fast/pounding heartbeat, hearing changes (such as ringing in the ears), mental/mood changes (such as confusion, depression), persistent/severe headache, stomach pain, sudden/unexplained weight gain, swelling of the hands or feet, vision changes (such as blurred vision). Tell your doctor immediately if any of these rare but serious side effects occur: easy bruising/bleeding, change in amount of urine, signs of infection (such as fever, chills, persistent sore throat), symptoms of meningitis (such as unexplained stiff neck, fever). This drug may rarely cause serious (possibly fatal) liver disease. Seek immediate medical attention if you have any symptoms of liver damage, including: dark urine, stomach/abdominal pain, persistent nausea/vomiting, yellowing eyes/skin. A very serious allergic reaction to this drug is rare. However, seek immediate medical attention if you notice any symptoms of a serious allergic reaction, including: rash, itching/swelling (especially of the face/tongue/throat), 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. In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.