MATTHEW PERRONEWASHINGTON (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.