Sept. 1 (Bloomberg) -- U.S. researchers found no evidence to support regulatory warnings that Merck & Co.'s Singulair asthma and allergy drug, taken by millions of Americans over the past decade, may be linked to depression or suicide.

The findings will be published in the Journal of Allergy and Clinical Immunology, the American Lung Association said in a statement on PRNewswire today. The study was sponsored by the association, which doesn't endorse products, it said.

American Lung Association researchers Janet Holbrook and Raida Harik-Khan re-analyzed data from patients who had taken part in Singulair's clinical trials for signals that may indicate an effect on a patient's emotional well-being. The found no deterioration in adults or children who received the Whitehouse Station, New Jersey-based company's drug. The U.S. Food and Drug Administration in March said Singulair, or montelukast, may be linked to suicide and changes in mood and behavior.

``Discovering adverse effects of a drug after it is on the market can be very difficult because the data are usually gathered from single events reported by doctors, which makes it is challenging to differentiate actual side effects from events unrelated to the drug,'' said Norman Edelman, the lung association's Chief Medical Officer, said in the statement.

``The value of this 'look back' study is that the investigators were able to compare a large group of patients given montelukast with those given a placebo, making a firm scientific conclusion possible,'' Edelman said.

Singulair was Merck's biggest product last year and the most-prescribed respiratory drug in the U.S., with worldwide sales growing 19 percent to $4.27 billion. Merck revised the drug's prescribing information in the past year to include reports of tremors, depression, suicide and anxiousness.

The FDA in March told doctors and patients to continue to use Singulair until more information becomes available. The regulator said in March it is working with the company to evaluate studies and patient reports.

To contact the reporter on this story: Angela Cullen in Frankfurt at acullen8@bloomberg.net

Last Updated: September 1, 2008 01:36 EDT