Drugs used by millions of patients to control epileptic seizures must carry warnings about heightened risks of suicide, federal regulators in the United States said.

The Food and Drug Administration announcement comes almost a year after the agency first said patients taking the drugs have a slightly higher risk for suicide than those taking dummy pills.

According to the new language, only about one in 500 patients faces an increased risk of suicidal thoughts and behaviour while taking the drugs. The new warning emphasizes that the risks are about the same among all anti-seizure drugs.

The FDA advised patients to consult their doctors before making any changes to their treatment.

The agency is also requiring manufacturers to distribute pamphlets that describe the risks for patients.

"All patients who are currently taking or starting on any antiepileptic drug for any indication should be monitored for notable changes in behaviour that could indicate the emergence or worsening of suicidal thoughts or behaviour or depression," FDA said in a statement Tuesday.

The new warnings apply to 21 medications, including blockbuster products like GlaxoSmithKline's Lamictal, Johnson & Johnson's Topamax and Pfizer's Lyrica.

Health Canada review

Many of the products are also sold in Canada.

"Health Canada experts are continuing their review of all available information concerning marketed anti-epileptic drugs in Canada to develop class labelling for these products," Health Canada spokesman Philippe Laroche said in an e-mail Tuesday.

Not strongest warning

The FDA stopped short of adding its sternest warning to the medications, as it had proposed earlier in the year.

In July, a panel of outside experts recommended against adding the so-called "black box" warning, the strongest available. Those experts and other physicians cautioned the agency that a boxed warning about suicide could alarm patients and cause them to stop taking their medications.

Anti-seizure drugs are used for a variety of illnesses besides epilepsy, including migraines, certain nerve-pain disorders, and psychiatric diseases such as bipolar disorder.

London-based Glaxo said it supports the decision to add information about suicide risks to its medication. However, the company added in a statement that it "remains confident in the overall safety and efficacy profile of Lamictal based on our extensive clinical trial experience and the experience of more than five million people worldwide."

FDA said in January its analysis of nearly 200 studies of 11 different epilepsy drugs showed patients taking the treatments were more likely to have suicidal thoughts and behaviours.

Seizure drugs were the fifth bestselling class of drugs in the U.S. last year, with sales over $10 billion US, according to pharmaceutical research firm IMS Health.

Pfizer said it would work with FDA to update labelling on Lyrica and Neurontin, an older drug which is approved to treat both epilepsy and nerve pain.

"Pfizer hopes that the labelling change will further facilitate important dialogue that should always occur between patients and their doctors."

Physician groups like the American Epilepsy Society pressured FDA in recent months to take a measured approach on the warnings, arguing they could cause more harm than good if patients stop taking the drugs.

Doctors have succeeded in curbing other FDA safety warnings in recent years. In 2004, regulators added a black box warning about suicide to antidepressant drugs. However, FDA scaled back the language last year after psychiatrists said it was causing patients to stop taking their medicines, putting them at even greater risk of suicide.