Montelukast is a prescription medication which is available only under the brand name Singulair. This medication belongs to a class of drugs known as leukotriene receptor antagonists. Here's how Singulair works: Leukotrienes are chemicals that are made in the body when it is exposed to an allergen. The result is inflammation of the airways. This medication enters the body and prevents certain cells from binding to create these leukotrienes, thereby lowering the risk of asthma or allergy attacks. Singulair is most commonly used in the prevention of asthma and seasonal allergic rhinitis, or hay fever. It can also treat exercise-induced broncho-constriction, which is a narrowing of the airways during intense physical activity. Singulair is available for infants as young as six months in oral granules, and for children in chewable tablets of 4 and 5 milligrams. A 10 milligram tablet is also available for older children and adults. This medication is generally taken once a day for allergy and asthma attack prevention. People with exercise-induced broncho-constriction usually take Singulair two hours before working-out. The most commonly reported side effects of Singulair include headache, dizziness, and mouth pain, but please ask your doctor for a complete list. Also, tell your doctor IMMEDIATELY if you experience worsening allergy or asthma symptoms, or other significant changes. Singulair should be used with caution in people who are taking Rifampin for tuberculosis. Ask your doctor for a full list of medications and conditions that should not be combined with Singulair. Singulair can be effective for preventing the symptoms of asthma and allergies. However, this medication must always be used under the direct care of a physician. Please ask for and review all of the patient information provided by your doctor before taking Singulair.