WASHINGTON (AP) ¿ U.S. regulators said Friday that new labels on popular asthma drugs like Merck's Singulair must highlight language about suicidal behavior, depression and anxiety seen in a small number of patients.

After 15 months of investigation, the Food and Drug Administration said Merck & Co. Inc. and Cornerstone Therapeutics, both based in the United States, and London-based AstraZeneca will have to raise label warnings about psychiatric problems reported by a handful of patients taking their drugs.

"Patients and healthcare professionals should be aware of the potential for neuropsychiatric events with these medications," the FDA said in a posting to its Web site.

A spokeswoman for Merck said the language already appears in Singulair's label, but will be raised to the "precautions" section. It's now listed in a section about various side effects reported by patients.

"We've been working with the FDA since Singulair came to market and every time we update the label it's in cooperation with them," said Merck spokeswoman Pamela Eisele.

Singulair was Merck's best-selling product last year, with U.S. sales of $3.5 billion.

A spokesman for AstraZeneca said new labeling on its drug would only mention two psychiatric problems: depression and insomnia.

A spokesman for Cornerstone Therapeutics had no immediate comment Friday evening.

FDA regulators began reviewing a handful of reports about mood changes, suicidal behavior and suicide in patients who had taken Singulair. The agency also launched probes into other drugs in the class, including AstraZeneca PLC's Accolate and Cornerstone Therapeutics Inc.'s Zyflo.

Earlier this year, the agency said company studies of the three drugs did not show an increased risk of suicidal behavior, though they were not designed to detect such problems. An FDA spokeswoman said Friday the agency is monitoring ongoing reports of suicide and other psychiatric problems among patients.

"We did move this language to the 'precautions' section to highlight that we're continuing to see these things," said FDA spokeswoman Karen Riley.

The exact language of the labeling updates has not been released, but the FDA said it could mention a slew of psychiatric problems, including: "agitation, aggression, anxiousness, dream abnormalities and hallucinations, depression, insomnia, irritability, restlessness, suicidal thinking and behavior ¿ including suicide ¿ and tremors."

In general, the FDA has started notifying the public earlier about possible safety issues with drugs after the agency came under fire for acting too slowly on drugs like Merck's painkiller Vioxx, which was removed from the market in 2004 because it doubled the risk of heart attack and stroke.

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