U.S. researchers re-examined data from patients who had taken part in Singulair trials, in order to track anything linking the Merck asthma and allergy drug with depression or suicide.

Researchers Janet Holbrook and Raida Harik-Khan didn’t spot any evidence connecting them, according to a statement released by the American Lung Association.

About five months ago, the U.S. Food and Drug Administration said that the consumption of Singulair, a medicine used to prevent asthma attacks in adults and children as young as 12 months old, may lead to suicide and changes in mood, as well as in behavior. The FDA's investigation may last up to nine months.

Last year, Merck & Co Inc. changed Singulair’s prescribing information, the new one including post marketing side effects such as tremors, anxiousness, depression and even suicide. The drugmaker claimed that none of the 11,000 patients in their 40 studies committed suicide, and that the investigation was activated by reports only, not studies.

As stated by Dr. Norman Edelman, the lung association's Chief Medical Officer and Professor of Preventive Medicine, Internal Medicine, and Physiology and Biophysics, “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.''

Also known as Montelukast, Singulair is available as oral tablets, chewable tablets, and oral granules. Enjoying an increased popularity, the product sales raised up to $4.3 billion in 2007.

The results of the study, which was funded by ALA, are to be published in the Journal of Allergy and Clinical Immunology.