Singulair is used to treat shortness of breath, or “wheezing”, due to asthma. Singulair is a type of leukotriene inhibitor. Leukotriene is a chemical produced by the body when allergens, such as pollens, are inhaled. These chemicals cause contraction and inflammation of the lungs and muscles around the airways in the body, causing asthma and breathing problems. Singulair’s total revenue since its approval in 1998 is $47.38 billion.