Reports say that Health Canada is also investigating the side effects of Singulair that reportedly is linked to Suicide.

"Merck said it recently added reports of suicide to Singulair's label, which already listed suicidal thinking and behaviour as reported side-effects," writes The Canadian Press.

Merck, in the website related to Singulair reports about the side effects of the Asthma treatment drug, writing the following:

Important Safety Information About Singulair

"SINGULAIR will not replace fast-acting inhalers for sudden symptoms. Continue to take your other asthma medicines as prescribed and have fast-acting medication available. For asthma, SINGULAIR should be taken once a day, in the evening as prescribed, whether or not you have asthma symptoms. If your symptoms get worse or you need to increase the use of your rescue inhaler, call your doctor at once.

"Side effects are generally mild and vary by age, and may include headache, ear infection, sore throat, and upper respiratory infection. Check with your doctor if you are pregnant or nursing. SINGULAIR should be taken once a day, as prescribed. SINGULAIR is available by prescription only.

"SINGULAIR has not been studied as a treatment option for both conditions in the same person.

This site (meaning Merck's site about Singulair) is intended only for residents of the United States, its territories, and Puerto Rico."

Singulair is Merck's biggest seller reports CBS. More than 31 Million prescriptions were filled in USA last year. While FDA says Singulair may have serious side effects, it will take the agency up to nine months to determine if any regulatory action is needed.