US government researchers have found that a widely prescribed asthma drug originally sold by Merck & Co may be linked to serious mental health problems for some patients, according to a scientific presentation reviewed by Reuters. The researchers found that the drug, sold under the brand name Singulair and generically as montelukast, attaches to multiple brain receptors critical to psychiatric functioning. Singulair was a blockbuster product for Merck after its launch in 1998, offering relief