Yet another Merck drug is under the FDA scanner.
The US body says it is investigating a possible link between Merck's best-selling drug Singulair and suicide.
The agency said it was reviewing a handful of reports involving mood changes, suicidal behavior and suicide in patients who had taken Singulair, the popular allergy and asthma drug.
Merck has updated the drug's labeling four times in the last year to include information on a range of reported side effects, including tremors, anxiousness, depression and suicidal behavior.
The F.D.A. said it had asked the company, based in Whitehouse, N.J., to dig deeper into its data on Singulair for evidence of possible links to suicide.
The agency said it had not established a "causal relationship" between Merck's drug and suicidal behavior. An agency spokeswoman said the review was prompted by three or four suicide reports it had received since last October.
It could take up to nine months before agency scientists can draw any conclusions, the F.D.A. said in a posting to its Web site.
Merck officials stressed that the agency's inquiry was based on reports, not clinical studies, which were the standard tool for evaluating drug safety. The company said none of the 11,000 patients enrolled in 40 Singulair trials had committed suicide.
Millions of patients in the United States take Singulair, which was first approved in 1998 and had sales of $4.3 billion last year.