Montelukast is a prescription medication used to prevent and manage asthma, relieve allergy symptoms, and protect against breathing difficulties triggered by exercise. Sold under the brand name Singulair, it works by blocking substances in your body called leukotrienes, which cause airway swelling, mucus production, and tightening of the muscles around your airways. It comes as a standard tablet, a chewable tablet, and oral granules, making it usable across a wide age range, from infants as young as 6 months to adults.
Asthma Prevention and Treatment
The primary use of montelukast is the ongoing prevention and treatment of asthma in patients 12 months and older. It’s taken once daily in the evening and is not a rescue inhaler. Instead, it works as a controller medication, reducing the underlying inflammation that makes airways reactive in the first place. In clinical studies of young children with early asthma, four weeks of montelukast improved a key measure of lung function by about 12%, compared to just 3.5% in children taking a placebo.
Montelukast starts working within about a day, though it may take longer to reach its full effect on symptom control. It’s often prescribed alongside other asthma medications, particularly inhaled corticosteroids, rather than as a standalone treatment. For many patients, it serves as an add-on that provides extra control when inhalers alone aren’t enough.
Exercise-Induced Breathing Difficulty
Some people experience airway tightening specifically during or after exercise, a condition called exercise-induced bronchoconstriction. Montelukast is approved to prevent this in patients 6 years and older. When used for exercise protection, it’s taken at least two hours before physical activity rather than as a daily evening dose. A single 10 mg oral dose provides significant protection starting at two hours, with the benefit persisting for up to 24 hours. You should not take a second dose within 24 hours of a previous one.
Seasonal and Year-Round Allergies
Montelukast is also approved for allergic rhinitis, both the seasonal type (hay fever) and the year-round variety triggered by dust mites, pet dander, or mold. It can relieve nasal congestion, sneezing, runny nose, and itching. For seasonal allergies, it’s approved for ages 2 and up. For year-round allergies, it’s approved from 6 months of age.
That said, montelukast is not the first choice for allergies on its own. In clinical comparisons, about 87% of patients on montelukast alone reported meaningful improvement in nasal symptoms, which is comparable to an antihistamine used alone. But nasal steroid sprays tend to outperform both: in one trial, about half the montelukast group still had uncontrolled symptoms after two weeks, while only a small fraction of the nasal steroid group did. Sneezing, in particular, responded much better to the spray.
Where montelukast really shines for allergies is in combination. Pairing it with an antihistamine produced greater symptom improvement than either medication alone, especially for sneezing. Current guidelines generally recommend montelukast for allergies only when other treatments haven’t worked well enough or aren’t tolerated.
How It’s Taken
For asthma and allergies, montelukast is taken once a day in the evening. The dose depends on age:
- Adults and teens 15 and older: one 10 mg tablet
- Children 6 to 14: one 5 mg chewable tablet
- Children 2 to 5: one 4 mg chewable tablet or one packet of 4 mg oral granules
- Infants 6 to 23 months: one packet of 4 mg oral granules (for year-round allergies only at this age)
For exercise-induced breathing problems, the same age-based doses apply, but you take it at least two hours before exercise instead of on a fixed daily schedule. If you’re already taking montelukast daily for asthma, you don’t take an extra dose before exercise.
The Boxed Warning on Mental Health Effects
In March 2020, the FDA added its most serious type of warning, a boxed warning, to montelukast’s label. The warning highlights reports of mental health and behavioral side effects that have occurred in some patients. These can include agitation, aggression, depression, anxiety, vivid or disturbing dreams, trouble sleeping, irritability, confusion, hallucinations, and in rare cases, suicidal thoughts or actions. Other reported effects include attention problems, memory issues, sleepwalking, tremor, and obsessive-compulsive symptoms.
These effects have been reported in both children and adults, and they can sometimes persist after stopping the medication. Not everyone experiences them, and for many patients montelukast causes no noticeable mood or behavioral changes. But the FDA considers the risk serious enough that patients and caregivers should be actively watching for any shifts in mood, sleep, or behavior after starting the medication. If changes appear, the recommendation is to stop taking it and talk to a prescriber promptly.
This warning is the main reason montelukast is now positioned as a second-line option for allergies rather than a first choice. For asthma, where the benefits of airway control are more significant, it remains a commonly used medication, but the mental health risk is part of the conversation when deciding whether to start it.
Common Side Effects
Beyond the mental health concerns, montelukast is generally well tolerated. The most frequently reported side effects in clinical trials were upper respiratory infections, headache, and stomach pain. In children, ear infections, sore throat, and cough were also common. These tend to be mild and overlap heavily with symptoms people would experience anyway, especially during allergy or cold season, which makes it hard to separate the medication’s effects from the conditions it treats.