Montelukast is used to prevent wheezing, difficulty breathing, chest tightness, and coughing caused by asthma in adults and children 12 months of age and older. Montelukast is also used to prevent bronchospasm (breathing difficulties) during exercise in adults and children 6 years of age and older. Montelukast is also used to treat the symptoms of seasonal (occurs only at certain times of the year), allergic rhinitis (a condition associated with sneezing and stuffy, runny or itchy nose) in adults and children 2 years of age and older, and perennial (occurs all year round) allergic rhinitis in adults and children 6 months of age and older. Montelukast should be used to treat seasonal or perennial allergic rhinitis only in adults and children who cannot be treated with other medications. Montelukast is in a class of medications called leukotriene receptor antagonists (LTRAs). It works by blocking the action of substances in the body that cause the symptoms of asthma and allergic rhinitis.