Epilepsy pills. Box and blister packs of Phenobarbitone pills used to treat epilepsy. Each pill contains 30 milligrams of the barbiturate drug phenobarbitone (or phenobarbital). Seizures in epilepsy are caused by uncontrolled and excessive electrical brain activity. Barbiturate drugs reduce brain activity, reducing the occurrence of seizures. They may also cause sedation, depression and addiction.