What is Montelukast (Singulair)? Montelukast contains leukotriene inhibitors. Leukotrienes are chemicals released by the body when breathing in an allergen. These chemicals cause swelling and inflammation of the lungs and constrict the muscles around the airways, leading to asthma symptoms. Montelukast is used to prevent asthma attacks in adults and children as young as 12 months. It is also used to relieve runny nose and sneezing due to allergies in adults and children as young as 6 months.











