Hyperplasia of the upper gums, a consequence of long-term use of the drug phenytoin in treating epilepsy. Overactive growth of the gums is a recognised side effect of phenytoin. Phenytoin is an anticonvulsant which reduces the severity of seizures in Grand mal epilepsy. Its mechanism of action involves increasing the membrane binding of calcium to stabilise excitable membranes & to decrease the availability of calcium for its role in the passage of nerve impulses.