Clonazepam is a drug that is used to treat panic disorder and epileptic seizures. The drug is thought to work by enhancing the effects of a naturally calming chemical in the brain. Clonazepam is taken by mouth, usually two or three times a day. Most people tolerate the drug well; however, side effects may occur. Possible side effects of clonazepam include drowsiness, coordination problems, and behavior problems.