If your asthma symptoms are not well controlled with a preventer inhaler, your GP may prescribe montelukast as an ‘add-on’ treatment

Health advice > Inhalers, medicines and treatments > Add-on asthma treatments

Find out how montelukast works as an add-on treatment for asthma, what the benefits are, and what important side effects to look out for.

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What is montelukast?

Montelukast is a type of medicine known as a leukotriene receptor antagonist.

Most people with asthma do not need montelukast, but it can be a useful add-on treatment to take alongside your usual preventer inhaler. Montelukast is not a steroid - it works in a different way to reduce inflammation.

Your GP or asthma nurse may prescribe montelukast (brand name Singulair) if you’re still getting asthma symptoms even though you’ve been taking your preventer inhaler as prescribed.

Is it suitable for everyone? 

Montelukast is suitable for most people with asthma. It is more commonly prescribed to children from six years old

Before taking montelukast, tell your GP if:

  • you have other health conditions
  • you’re taking any other medicines
  • you’re pregnant or planning to get pregnant
  • you’re breastfeeding.

How do you take it? 

Montelukast comes as a tablet, a chewy tablet, or granules.

  • Montelukast tablets to swallow with water are for adults and children over 15.
  • Chewable tablets are available for children aged two to 14.
  • Granules are available for younger children. These can either be sprinkled directly into the child’s mouth, or placed on a spoonful of cold (or room temperature) food, for example pureed fruit or yogurt.


Keep taking your preventer inhaler

Do not stop taking your preventer inhaler, even if you notice your asthma symptoms improving after taking montelukast. 

If you stop taking your preventer inhaler it could cause your symptoms to get worse again. 

How does montelukast help asthma?

Montelukast can help people with asthma whose symptoms are not well controlled with a preventer inhaler alone. For some people it is a good alternative to higher doses of inhaled steroids.  

If you take montelukast as prescribed it can help your asthma by:

  • calming the inflammation in your airways so it’s easier to breathe
  • improving asthma symptoms
  • reducing the need for your reliever inhaler
  • stopping airways narrowing triggered by exercise
  • blocking chemicals called leukotrienes which make your airways inflamed when you have an allergic reaction, for example to pollen (hay fever).

Your GP or asthma nurse should review your treatment four to eight weeks after you start taking montelukast.

If montelukast has had no effect after you’ve been taking it for four to eight weeks, you can talk about other treatment options.

Don’t stop taking it before speaking to your GP or asthma nurse. Your asthma symptoms may get worse and you may increase your risk of an asthma attack.

Side effects of montelukast

Like all medicines, montelukast can cause side effects. Often, side effects can go, or improve, after two to three weeks of taking the medicine. 

  • Common side effects (affecting around 1 in 10 to 1 in 100 people) include diarrhoea, stomach-ache, sore throats and infections.
  • Less common side effects (affecting around 1 in 100 to 1 in 1000 people) include sleep issues such as insomnia, nightmares or sleepwalking, and mood changes such as anxiety, depression, and irritability.
  • Very rare potential side effects (affecting fewer than 1 in 10,000 people) include severe mental health disturbances and suicidal thoughts.

“Severe mental distress is an extremely rare side effect, but where it has happened it is extremely worrying and upsetting,” says Dr Andy Whittamore, Asthma UK’s in-house GP.

  • If you, or your child, show signs that montelukast is affecting your mood talk to your GP or asthma nurse as soon as possible.
  • If you or your child show signs of extreme distress, or have suicidal thoughts, stop taking the medicine immediately. Call 999 or go to A&E.

Always read the patient information leaflet so you’re aware of what side effects to look out for, and when you need to go straight back to your GP or asthma nurse.

You can report any serious side effects yourself through the yellow card scheme. Or you can ask your doctor to do it for you.


Get help urgently if montelukast is affecting your mood

If you feel extremely distressed, or suicidal, stop taking the medicine. Get immediate help by calling 999 or going to your nearest A&E.



You can call our Helpline on 0300 222 5800 to speak to a respiratory nurse specialist, Monday to Friday, 9am-5pm. Or you can WhatsApp them on 07378 606728.


Last updated April 2021

Next review due April 2024

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