What is Singulair? Singulair is used regularly to prevent the wheezing and shortness of breath caused by asthma and decrease the number of asthma attacks. Singulair 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 rescue inhaler. This medication is also used to relieve symptoms of hay fever and allergic rhinitis (such as sneezing, stuffy/runny/itchy nose).