It can have serious side effects. Immediately consult your physician if you start experiencing any of the following side effects: Sleep problems (insomnia), Unusual changes in mood or behavior, Manic episodes like racing thoughts, increased energy, reckless behavior, feeling extremely happy or irritable, talking more than usual, severe sleep problems, Blurred vision, tunnel vision, eye pain or swelling, or seeing halos around lights, Anxious feeling, Dizziness, Joint pain, Dry mouth, Stuffy nose, Nausea, Constipation, Convulsions, seizure, Fast heartbeats, Severe skin reaction, Fever, Anxiety, panic attacks, aggressive, hyperactive, Suicidal thoughts