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Montelukast is a leukotriene receptor antagonist that reduces airway swelling and inflammation. It is used for asthma and, in some circumstances, allergies. It does not treat an acute asthma attack. The FDA advises reserving its use for hay fever for people whose other treatments have not worked or are not tolerated.
Does it replace my inhalers?
No. Keep using your preventer and reliever inhalers as directed. Stopping a preventer may make asthma worse.
What are the common side effects?
Stomach pain, diarrhoea, headache, mild rash, high temperature and feeling sick can occur.
What is the mood and behaviour warning?
Serious mood, behaviour and sleep changes have been reported, including nightmares, agitation, depression and suicidal thoughts or actions. Stop montelukast and contact a healthcare professional immediately if new or worsening symptoms occur. Tell family and carers what to watch for.
Seek emergency help if you or your child are in immediate danger of self-harm. Do not wait for a website reply.
Who should tell their doctor first?
Tell your doctor if you have a mental health condition such as depression or anxiety, are pregnant or breastfeeding, have galactose intolerance, or have reacted to a medicine before.
When should I get help?
Contact your doctor urgently for shaking, a fast or unusual heartbeat, speech changes, pins and needles, numbness or yellowing of the eyes. Call your local emergency number (000 in Australia) for a severe allergic reaction.
Doses and formulations vary. Follow your prescriber, pharmacist and the leaflet supplied with your exact medicine. In Australia, call 000 for a medical emergency or the Poisons Information Centre on 13 11 26 for suspected poisoning or overdose. Outside Australia, use your local emergency and poison-information services.
Sources: Asthma + Lung UK: Montelukast; TGA montelukast safety warning; FDA boxed warning. General education does not replace individual medical advice. Updated November 2026.
Read more in our Health Guides. For website or catalogue questions, contact support; urgent medical concerns need a healthcare service.