Montelukast is a selective antagonist of the leukotriene D (LTD) receptor. In patients with asthma, montelukast 5 to 250 mg/day attenuated LTD-induced bronchoconstriction and, at a dosage of 10mg, significantly reduced early and late airway response to allergen (dust mite extract) relative to placebo.
In studies evaluating the effects of various dosages of montelukast on exercise-induced bronchoconstriction the optimal dose of the drug was found to be 10mg.
Montelukast 10 mg/day controlled asthma significantly more effectively than placebo in a 3-month randomised double-blind study. In a 9-month open extension of this trial, during which patients were randomised to treatment with montelukast 10 mg/day or beclomethasone (
400 µg/day), daytime symptom score and 
-agonist use decreased to a similar extent in each group.
In a further study, treatment with montelukast 10 mg/day permitted clinically significant tapering of corticosteroid dosage in patients with stable asthma.
Montelukast (5 mg/day) has also demonstrated efficacy in childhood asthma.
The tolerability profile of montelukast was similar to that of placebo in placebo-controlled clinical trials in adults and children; the most common adverse event was headache.