Anticonvulsant: A medication used to control (prevent) seizures (convulsions) or stop an ongoing series of seizures. There are a large number of anticonvulsant drugs today including, but not limited to: phenobarbital, phenytoin (Dilantin), carbamazepine, ethosuximide (Zarontin), clonazepam (Klonopin), diazepam (Valium), lorazepam (Ativan), and midazolam (Versed). Anticonvulsant drugs taken during pregnancy put the baby at risk of major birth defects -- growth retardation, microcephaly (a small head) and deformities of the face and fingers -- a condition known as anticonvulsant embryopathy.