Montelukast: what it treats, how to take it, side effects
Last updated September 3, 2026.
Montelukast is a daily pill that blocks the body chemicals behind asthma symptoms and allergies. You may know it as Singulair. It is a leukotriene receptor antagonist - a preventer, never a rescue - and it carries a boxed warning about serious mental health changes.
What does it treat?
Prevention of wheezing, difficulty breathing, chest tightness, and coughing from asthma in adults and children 12 months and older; prevention of exercise-induced breathing difficulty (a dose at least 2 hours before exercise); and seasonal or perennial allergic rhinitis - but only in people who cannot be treated with other medications, per MedlinePlus. One line that matters: it does not treat a sudden asthma attack. Your short-acting inhaler handles those.
How do you take it?
Once a day, with or without food, same time each day - in the evening for asthma (the label's adult dose is one 10 mg tablet), any consistent time for allergies. For exercise-induced symptoms, take it at least 2 hours before, and never double up if you already had a dose in 24 hours. Granules for young children go directly in the mouth or mixed into a teaspoon of cold or room-temperature baby formula, breast milk, applesauce, soft carrots, ice cream, or rice, used within 15 minutes. Keep taking all your other asthma medications unless your doctor says otherwise. Missed dose: skip it - never take more than one dose in 24 hours.
Side effects to know
- Common: headache, heartburn, stomach pain, tiredness, and diarrhea.
- Serious - the boxed warning: montelukast may cause serious or life-threatening mental health changes, even in people with no history of mental illness. Stop taking it and call your doctor right away for agitation, aggressive behavior, anxiety, irritability, attention or memory problems, confusion, unusual dreams, hallucinations, repeating thoughts you cannot control, depression, insomnia, restlessness, sleepwalking, suicidal thoughts or actions, or tremor. Family should know this list too. Also serious: allergic reactions - trouble breathing or swallowing, swelling of the face, throat, tongue, lips, or eyes, hoarseness, itching, rash, hives.
Who should not take it?
Tell your doctor if you have or have ever had any mental illness - though the warning applies even without one. Flag liver disease, and mention gemfibrozil, phenobarbital, and rifampin, which can change levels. If your asthma is made worse by aspirin, do not take aspirin or other NSAIDs while on montelukast. The chewable tablets contain aspartame, which matters for PKU. Pregnant, planning pregnancy, or breastfeeding: tell your doctor first.
When is it an emergency?
Trouble breathing or swallowing, or facial or throat swelling, is a 911 call. Any mental health change - especially thoughts of harming or killing yourself - means stopping the medication and calling your doctor right away; you can also call or text 988, the Suicide and Crisis Lifeline, any time. For an overdose, call Poison Control at 1-800-222-1222. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
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Common questions
Why does montelukast have a boxed warning?
Because of mental health. MedlinePlus's warning says montelukast may cause serious or life-threatening mental health changes - during treatment or after stopping - even in people with no history of mental illness: agitation, aggression, anxiety, hallucinations, depression, sleepwalking, suicidal thoughts or actions. Stop the medication and call your doctor right away if any appear, and make sure family knows the signs.
Can montelukast stop an asthma attack in progress?
No. MedlinePlus says do not use montelukast to treat a sudden attack of asthma symptoms - your doctor prescribes a short-acting inhaler for that. Montelukast is daily prevention; it lowers the odds and severity of attacks over time but does nothing for one already happening.
Why do I take montelukast at night?
The label recommends evening dosing for asthma - one 10 mg tablet once daily in the evening for adults - since symptoms and airway inflammation tend to peak overnight. For allergic rhinitis, the label says morning or evening both work, so your doctor can individualize it. Whatever time you pick, keep it consistent.
Can I take montelukast only when my allergies flare?
It is built as a daily controller, not an as-needed pill - MedlinePlus says it controls symptoms but does not cure them, and to continue taking it even if you feel well. If your allergies are occasional, ask your doctor whether daily montelukast is even the right tool; it is reserved for people who cannot be treated with other allergy medications.
Can I drink alcohol while taking montelukast?
Neither the FDA label nor MedlinePlus lists a specific alcohol interaction for montelukast. Given the medication's mental health warning, anything that affects mood, sleep, or judgment is worth a cautious conversation with your doctor.
Is montelukast a steroid?
No. It is a leukotriene receptor antagonist - it blocks the action of substances in the body that cause asthma and allergy symptoms, per MedlinePlus. It works alongside inhaled steroids, not as one, and you should not stop any other asthma medication unless your doctor tells you to.