WASHINGTON (AP) -- The Food and Drug Administration said Thursday it is investigating a possible link between Merck's best-selling Singulair and suicide.
FDA said it is reviewing reports of mood changes, suicidal behavior and suicide in patients who have taken the popular allergy drug.
Merck has updated the drug's labeling four times in the past year to include information on a range of side effects: tremors, anxiousness, depression and suicidal behavior.
FDA said it asked the Whitehouse, N.J.-based company to dig deeper into its data on Singulair for more evidence of possible links to suicide. It could take up to nine months before agency scientists can draw any conclusions, FDA said in a posting to its Web site.
Merck officials stressed that FDA's inquiry is based on a small number of suicide reports and not clinical studies, which are used to evaluate drug safety. The company said none of the 11,000 patients enrolled in 40 Singulair trials has committed suicide.
"We have no indication that anything about the mechanism of Singulair is consistent with these events," said George Philip, director of research and product development. "But because suicide is a life-threatening event we thought it was important to provide this information in the product label."
Merck said it recently added reports of suicide to Singulair's label, which already listed suicidal thinking and behavior as possible side effects.
With sales of $4.3 billion last year, Singulair is used by millions of patients in the U.S, according to Merck. First approved in 1998, it's part of a class of asthma and allergy drugs that includes AstraZeneca's Accolate and Critical Therapeutics's Zyflo.
FDA said it is also reviewing reports of side effects with those drugs. Their labeling does not contain reports of suicide.
Shares of Merck & Co. Inc. fell 4 cents to $44.67 in midday trading.