This medication may cause stomach upset, diarrhea, nausea, headache, itching and fatigue during the first few days as your body adjusts to the medication. If these symptoms persist or become severe, inform your doctor. Notify your doctor immediately if an allergic reaction occurs while taking this medication. Symptoms include: skin rash, itching, difficulty breathing, hives, chest pain, facial swelling. If you notice other effects not listed above, contact your doctor or pharmacist.