Side effects of carbamazepine (CBZ), valproate (VPA) and clonazepam (CZP) are rare during long-term use but rather common and usually transient during the early phases of treatment. The usual side effects of CBZ are drowsiness, dizziness, and diplopia, which are dose dependent in long-term use, but CBZ does not seem to cause cognitive disturbances, as do phenobarbital and phenytoin. Other reactions to CBZ may include leukopenia, hyponatremia, disturbances of vitamin D metabolism and fortunately rarely, agranulocytosis and hepatitis. Use of VPA can lead to gastrointestinal discomfort, weight gain, hair loss, tremor and sedation, but these side effects are rather uncommon, mild, and transient during VPA monotherapy. Potentially hazardous reactions such as hepatitis and pancreatitis have occurred in a few patients on VPA, generally with multidrug therapy. Some of the side effects are dose related. They infrequently lead to withdrawal of VPA. Side effects limited to initiation of CZP therapy include drowsiness, ataxia, and behavioral changes; they are usually transient but can lead to dose reduction or even withdrawal of the drug. Except for development of tolerance, CZP seems to be practically free of long-term side effects.