Montelukast sodium is a prescription medication that reduces inflammation and opens the airways by blocking chemicals in your body called leukotrienes. Sold under the brand name Singulair, it is used to manage asthma, prevent exercise-triggered breathing problems, and relieve allergy symptoms like sneezing, congestion, and a runny nose. Unlike an inhaler that delivers medication directly to your lungs, montelukast is a pill you take once a day by mouth.
How Montelukast Works in Your Body
Your immune system produces inflammatory chemicals called leukotrienes when it encounters allergens or other triggers. These chemicals latch onto receptors in your airway cells, including smooth muscle and immune cells, and cause a chain reaction: the airway lining swells, the muscles around the airways tighten, and mucus production increases. The result is the wheezing, chest tightness, and congestion familiar to people with asthma or allergies.
Montelukast works by sitting on those same receptors first, physically blocking leukotrienes from attaching. Because it occupies the receptor without activating it, the swelling, muscle contraction, and excess mucus never get triggered in the first place. Clinical studies show this translates into real improvements: reduced need for rescue inhalers, fewer asthma symptoms, lower levels of inflammatory cells in the blood, and better airflow measured by morning breathing tests.
Approved Uses
Montelukast has three distinct FDA-approved uses, each covering slightly different age ranges:
- Long-term asthma management. Approved for adults and children 12 months and older. It is used to prevent asthma attacks over time, not to stop an attack already in progress.
- Exercise-induced breathing difficulty. Approved for patients 15 years and older (the FDA label for Singulair also references age 6 and older in certain contexts). You take it at least two hours before physical activity so the drug reaches effective levels by the time you start exercising. A single dose provides significant protection for up to 24 hours.
- Allergic rhinitis (hay fever). For seasonal outdoor allergies, it is approved in patients 2 years and older. For year-round indoor allergies, it is approved down to 6 months of age. It helps with sneezing, nasal congestion, runny nose, and nasal itching.
How It Is Taken
Montelukast is a once-daily medication. The dose depends on age:
- Ages 15 and older: one 10 mg film-coated tablet
- Ages 6 to 14: one 5 mg chewable tablet
- Ages 2 to 5: one 4 mg chewable tablet or one packet of 4 mg oral granules
- Ages 6 to 23 months: one packet of 4 mg oral granules
For asthma, the tablet is typically taken in the evening. For allergic rhinitis, timing is more flexible. The drug begins working within about a day for asthma symptoms. If you notice no improvement after four to eight weeks, that is generally a sign to discuss alternatives with your prescriber. For exercise-induced symptoms, the onset is faster: protection kicks in as early as two hours after a single dose.
What Montelukast Does Not Do
Montelukast is a preventive, maintenance medication. It will not relieve an asthma attack that is already happening. You still need a fast-acting rescue inhaler for sudden symptoms. It also does not replace inhaled corticosteroids for people whose asthma requires them, though it can be added alongside other treatments to improve overall control.
Because it targets only the leukotriene pathway, montelukast addresses one piece of the inflammation puzzle. Some people respond strongly to it while others see only modest benefit, depending on how much of their symptoms are driven by leukotrienes versus other inflammatory signals.
The FDA Boxed Warning on Mental Health
In 2020, the FDA added its strongest safety warning (a boxed warning) to montelukast after reviewing reports of serious neuropsychiatric side effects. These include agitation, depression, sleep disturbances, suicidal thoughts, and behavioral changes. The effects have been reported in both adults and children.
Because of this warning, the FDA advises that montelukast should be reserved for patients with allergic rhinitis only when other allergy treatments have not worked or are not tolerated. For asthma, the benefit of breathing control may outweigh the risk, but you should be aware of potential mood or behavior changes after starting the medication. These effects can appear days to weeks into treatment and typically resolve after stopping the drug.
Common, Less Serious Side Effects
Outside of the neuropsychiatric concerns, montelukast is generally well tolerated. The most frequently reported side effects in clinical trials were upper respiratory infections, headache, sore throat, and cough. In children, ear infections and stomach upset were also common. These overlap with symptoms of the conditions being treated, so they can be easy to overlook or misattribute.