Phenobarbital is a commonly prescribed anti-convulsant, commonly used in the treatment of epilepsy and other seizure disorders. It is related to the barbituates. It was first marketed as a sedative in 1912, and it's anti-convulsant effects were first noted in experiments performed with epilepsy patients shortly thereafter. It quickly replaced bromide as it worked better and had fewer side effects. However, it was soon found that withdrawal from the drug brings on further seizures, meaning that it generally had to be used for life. It did allow institutionalized patients to be released and even return to employment.
Phenobarbitol's use as a sedative was phased out in the 1950s as benzodiazepines came into use. It's use as an anti-convulsant has also declined with the development of modern alternatives which have fewer side effects.