Montelukast (Singulair) is a drug that relieves allergy symptoms and is also used to prevent asthma attacks. It reduces congestion in your nose and also cuts down on sneezing, itching, and eye allergies. For people with allergies and asthma, it helps keep airways to your lungs open.
It works by stopping the action of a chemical called leukotriene, which causes your nasal passages to swell and make a lot of mucus. The same chemical is also responsible for tightening airways when you have asthma, making it harder to breathe.