Buy Singulair online, a prescription medication used to treat the following conditions: asthma, including exercise-induced asthma, allergic rhinitis (irritated, stuffy, itchy, or runny nose due to allergies). Generic Singulair belongs to a class of medications called leukotriene modifiers. Leukotrienes are substances produced by the body in response to allergens or other problems. In the lungs, they provoke swelling and inflammation in the airways and constriction of the muscles of the respiratory tract. In the nose, leukotrienes are liberated after exposure to allergens (substances that cause allergies), leading to allergy symptoms. This med works by blocking leukotriene receptors, preventing these chemicals from causing allergy or asthma symptoms.