Lyng Pharmacy
Medicines A–Z · Leukotriene receptor antagonist

Montelukast

Also sold as Singulair · Written by the Lyng Pharmacy team, based on NHS and BNF guidance · Updated August 2026
Also sold asSingulair
Type of medicineLeukotriene receptor antagonist
Available asTablets, chewable tablets, granules
How you get itPrescription only

Montelukast is a preventer taken as a tablet rather than an inhaler, used alongside inhaled treatment in asthma. It works well for some people, particularly where allergy or exercise is a big trigger — and it carries an important warning about mood and behaviour that everyone taking it should know.

What it is used for

Preventing asthma symptoms, particularly where allergy or exercise is a major trigger, and relieving seasonal allergic rhinitis in people who also have asthma. It is often added when an inhaled steroid alone is not enough.

It is a preventer, not a reliever. It does nothing for an asthma attack — your blue inhaler does that.

How to take it

Once daily in the evening. Chewable tablets are chewed; granules can be given directly in the mouth or mixed with a spoonful of soft food such as yoghurt or apple purée, and used within 15 minutes.

Take it every day, not only on bad days. It can take a few days to show benefit.

For exercise-induced symptoms specifically, the dose is sometimes taken a couple of hours before exercise — follow what you have been told.

Mood and behaviour — the warning that matters

Montelukast can cause changes in mood and behaviour, including sleep disturbance, vivid dreams and nightmares, anxiety, agitation, depression, and rarely thoughts of self-harm. These can occur in adults and children, at any point during treatment. Stop taking it and contact your doctor promptly if any of these develop.

This is not a rare small-print caution — it is the main reason montelukast is stopped, and parents should be told to watch for it in children. If you are having a difficult time and need to talk to someone now, Samaritans are on 116 123, free, at any hour.

Other side effects

Headache, stomach ache, thirst, and cold-like symptoms are the more common ones.

Get medical advice for a rash, wheezing that worsens, or unusual bruising.

Never stop your inhaled preventer because montelukast has been added, unless your prescriber tells you to.

Always read the label. This page is general information, not advice for your situation. Doses, warnings and interactions differ between products and between people. Check the leaflet inside your medicine, and ask our pharmacist if anything is unclear — that conversation is free and takes two minutes.

Questions about Montelukast?

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Frequently asked questions

When should I take montelukast?
Once daily in the evening, every day rather than only when symptoms are bad.
Can montelukast affect mood?
Yes. Sleep disturbance, nightmares, anxiety, agitation, depression and rarely thoughts of self-harm can occur in adults and children. Stop and contact your doctor promptly if they develop.
Is montelukast a reliever inhaler replacement?
No. It is a preventer taken as a tablet. Your blue reliever inhaler is what treats symptoms and attacks.
Can children take montelukast?
Yes, in age-appropriate forms, but parents should watch closely for changes in mood, sleep or behaviour and report them promptly.

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