Drooling, drowsiness, dizziness, headache, shaking (tremor), vision problems (e.g., blurred vision) and constipation may occur. Many of these effects (especially drowsiness) lessen as your body gets used to the medication. If any of these effects persist or worsen, contact your doctor or pharmacist promptly. To prevent constipation, maintain a diet adequate in fiber, drink plenty of water, and exercise. If you become constipated while using this drug, consult your pharmacist for help in selecting a laxative (e.g., stimulant-type with stool softener). 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: facial/muscle twitching, signs of infection (e.g., severe tiredness, fever, persistent sore throat), seizures, uncontrollable movements, change in the amount of urine. Seek immediate medical attention if any of these rare but very serious side effects occur: high fever, fast/irregular heartbeat, muscle stiffness, mental/mood changes, difficulty breathing with exercise, swollen legs/feet, sudden weakness, pain/redness/swelling of the arms/legs, chest pain, dark urine, persistent nausea/vomiting, stomach/abdominal pain, yellowing of eyes/skin. A very serious allergic reaction to this drug is unlikely, but seek immediate medical attention if it occurs. Symptoms of a serious allergic reaction may include: 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.