Montelukast is used to control and prevent symptoms caused by asthma (such as wheezing and shortness of breath). It is also used before exercise to prevent breathing problems during exercise (bronchospasm). This medication can help decrease the number of times you need to use your quick relief inhaler. Montelukast is also used to relieve symptoms of hay fever and allergic rhinitis (such as sneezing, stuffy/runny/itchy nose). Since there are other allergy medications that may be safer (see also Warning section), this medication should be used for this condition only when you cannot take other allergy medications or they do not work well. This medication must be used regularly to be effective. It does not work right away and should not be used to relieve sudden asthma attacks or breathing problems. If an asthma attack or sudden shortness of breath occurs, use your quick-relief inhaler as prescribed. This drug works by blocking certain natural substances (leukotrienes) that may cause or worsen asthma and allergies. It helps make breathing easier by reducing swelling (inflammation) in the airways.