Common side effects may include headache, agitation, drowsiness, constipation, dry mouth, upset stomach, vomiting and diarrhea. Serious side effects may include very stiff (rigid) muscles, high fever, tremors, sweating, confusion, fast or uneven heartbeats, slow heart rate, feeling like you might pass out; twitching or uncontrollable movements of your eyes, lips, tongue, face, arms, or legs; trouble speaking or swallowing; dry mouth, thirst, feeling very hot (with or without sweating), urinating less than usual or not at all;high blood sugar(increased thirst, loss of appetite, fruity breath odor, increased urination, drowsiness, dry skin, nausea, and vomiting); sudden numbness or weakness, confusion, or problems with vision, speech, or balance; fever, chills, body aches, flu symptoms, sores in your mouth and throat; swelling in your hands or feet; changes in personality, unusual thoughts or behavior, hallucinations, or thoughts about hurting yourself; or upper stomach pain, itching, loss of appetite, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes). This is not a complete list of side effects and others may occur. Call your doctor for medical advice about additional side effects that you may experience.