After several reports of suicide, asthma and allergy drug Singulair is being investigated by Health Canada and the FDA for a possible link to mood changes and suicidal behaviour in patients using this drug.
Links
[1] http://www.fda.gov/cder/drug/early_comm/montelukast.htm
[2] http://www.merck.com/newsroom/press_releases/product/2008_0327.html