Montelukast: what it does and what to watch
Also known as: montelukast sodium · Leukotriene receptor antagonist · Updated 2026-08-19 · Educational — not medical advice
In plain language: Montelukast blocks leukotrienes, chemical messengers the immune system releases that tighten airway muscles and trigger swelling and mucus production. By keeping leukotrienes from docking onto their receptors, it helps keep airways calmer and less reactive over time, though it works too slowly to relieve a sudden asthma attack in progress.
What it's used for
- Long-term control of asthma
- Prevention of exercise-induced breathing symptoms
- Seasonal allergic rhinitis symptoms
Common side effects
- Headache
- Stomach pain
- Fatigue
- Cough
- Fever (more common in children)
Get medical help if…
Get medical help if you or your child notice mood or behavior changes, such as agitation, aggression, anxiety, depression, sleep disturbances, or thoughts of self-harm; these are recognized boxed-warning effects that warrant prompt evaluation
Get medical help if you develop hives, facial swelling, or breathing difficulty (possible allergic reaction)
Get medical help if you notice yellowing of the skin or eyes, which can indicate liver involvement
Get medical help if asthma symptoms worsen or rescue inhaler use increases, since montelukast is not a rescue treatment
Lab values it can move
Few guides tell you this part: medicines show up in blood work. If you take Montelukast and a value below looks off on your report, this may be part of the story — never stop a medicine without your doctor.
Montelukast is processed by the liver, and uncommon cases of elevated ALT have been reported, so this marker offers a way to check how the liver is handling the medication over time.
SGPT (ALT)Good to know
- Montelukast is a daily preventer, not a rescue medicine; it won't stop a breathing attack that has already started
- Be alert for any new mood, behavior, or sleep changes in yourself or a child taking it, and discuss them with a healthcare provider promptly
- Continue any prescribed rescue inhaler as directed, since montelukast doesn't replace it
- Mention any liver conditions before starting, given its route of processing
Questions people ask
Why does montelukast carry a warning about mood changes?
Regulatory agencies added a boxed warning after reports linking montelukast to behavioral and mood changes, including agitation, anxiety, depression, sleep problems, and, rarely, suicidal thoughts, particularly noted in children and teenagers. It doesn't happen to everyone, but knowing the signs means changes can be caught and discussed with a healthcare provider quickly.
Can montelukast stop an asthma attack once it starts?
No. Montelukast works gradually in the background to reduce airway inflammation and reactivity over days to weeks, so it has no role in relieving a breathing attack that's already underway. Rescue inhalers remain the tool for sudden symptoms, and montelukast is meant to reduce how often those episodes occur.
Taking Montelukast? See what your blood work says.
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