Please consult your personal physician before taking any medication. Singulair Oral Uses: Montelukast is used as a long-term (maintenance) treatment to prevent or treat asthma. It may also be used in people older than 14 years to prevent asthma brought on by exercise (bronchospasm). This medication is also used to treat allergic rhinitis, also known as allergies or hay fever. Montelukast works by blocking certain substances (leukotrienes) in the body. This effect helps to decrease symptoms (e.g., breathing problems, sneezing, stuffy/runny/itchy nose) caused by asthma or allergies. Singulair may also be used for purposes other than those listed in this medication guide.