Overall, four people in the drug-treated groups committed suicide, and none in the placebo groups.

What that means: For every 1,000 patients, about two more drug-treated patients experienced suicidal thoughts than placebo-takers, FDA concluded.

Anti-seizure drugs are used for a variety of illnesses in addition to epilepsy, including migraines and psychiatric diseases. The FDA found that drug-treated patients were at increased risk no matter their diagnosis but that the risk was highest for epilepsy patients.

The FDA analyzed data from 11 well-known anti-seizure drugs, including Neurontin, Tegretol and Depakote, but the agency said it expected the risk applied to every epilepsy drug. The FDA said it would work with manufacturers to add the warning to product labels.