Merck's Singulair Scrutinized for Safety by FDA

U.S. regulators on Thursday said they are probing a possible connection between Merck'sSingulair asthma drug and suicidal behavior.

The FDA said it is reviewing the issue after receiving reports of mood and behavior changes, suicidal thinking and suicide in patients who took the drug, which is used to treat stuffy nose, sneezing and other allergy symptoms as well as asthma.

The agency did not say how many reports it had received. (See more in the video at left.)

While no definite link to the drug has been established, the FDA said it has asked Merck to evaluate its data for more information on the risk. The agency said it expects it to take up to nine months to finish its own review.

The FDA said it is also reviewing reports of behavioral changes in patients taking other similar drugs, including AstraZeneca'sAccolate and Critical Therapeutics Inc's Zyflo but has not yet decided whether further investigation is needed.

Merck earlier added information about the risk of tremors, depression, anxiousness and suicidal behavior to Singulair's label.

Representatives for Merck had no immediate comment.

Merck's shares were down marginally on the New York Stock Exchange.