Phenobarbital has been used to treat epilepsy since the early decades of the 20th century. It is still commonly used throughout the world because it is both effective and low in cost. Also, most people need to take it only once a day, so they are less likely to miss doses.

Phenobarbital is useful in controlling simple and complex partial seizures and generalized tonic-clonic seizures in patients of all ages. It has often been considered the first choice to treat certain kinds of seizures in infants.

In studies of seizure medicines, some people do better with phenobarbital and others do better with something else. It's difficult to forecast the results for any given person. Differences in side effects may be important in deciding which medicine is best for each person.

Some doctors hesitate to prescribe phenobarbital because it has a reputation for causing unwanted side effects, especially sleepiness in adults and problems with behavior or learning in children. Side effects are much more likely to be troublesome if a high dose is given, especially at the beginning. It may be necessary to increase the amount used very slowly over several months. Side effects are more common when phenobarbital is first taken or when the dose is increased, but not everyone is affected and some people can take high doses without trouble.

If seizures continue, the doctor probably will change the amount of phenobarbital prescribed. If that doesn't work, the next step may be either to prescribe a different seizure medicine by itself or to prescribe a combination of phenobarbital and another seizure medicine. Many are available. No single combination is best for everyone. Phenobarbital is often used as an "add-on" medicine for people who continue to have seizures while taking other seizure medicines. It does interact with many other medicines, so the amount taken may need to be adjusted if a combination is used.

Reviewed February 2004 by Steven C. Schachter, MD, epilepsy.com Editorial Board.