Washington, D.C. ? Epilepsy drugs used by millions of people may increase the risk of suicidal thoughts or behavior, the Food and Drug Administration warned Thursday in an alert to doctors.

The FDA analyzed almost 200 studies of 11 anti-seizure drugs, some that have been on the market for decades. The studies tracked almost 28,000 people given the medications and another 16,000 given dummy pills.

Very rarely were suicidal thoughts or behavior reported. Still, the FDA found that drug-treated patients did face about twice the risk: 0.43 percent of drug-treated patients experienced suicidal thoughts or behavior, compared with 0.22 percent of placebo-takers.

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, the FDA concluded.

An FDA spokeswoman said only that patients should ask a doctor before making medication changes.