Please note that Singulair is not a bronchodilator and should not be used as rescue medication in acute asthmatic episodes. These chemicals cause swelling in your lungs and tightening of the muscles around your airways, which can result in asthma symptoms to your doctor immediately. Singulair is steroid-free and offers the convenience of a once-daily tablet. Singulair is a prescription tablet, approved to help control asthma in adults and to relieve symptoms of indoor as well as outdoor allergies. To help people with asthma do something that the rest of us take for granted breathe.