What is montelukast and what conditions does it treat?

Montelukast, brand name Singulair, is a leukotriene receptor antagonist that blocks leukotrienes, inflammatory mediators that cause bronchoconstriction, mucus production, and airway edema. It is used for asthma prevention, exercise-induced bronchoconstriction, and allergic rhinitis. Montelukast is taken once daily and is not a rescue medication. The FDA issued a black box warning in 2020 for neuropsychiatric side effects including agitation, depression, suicidal thinking, and sleep disturbances.