Montelukast is used to prevent the symptoms of asthma. It's usually prescribed when asthma is mild and can stop it from getting worse.

It can also help people with asthma who have breathing difficulties when they exercise (exercise-induced asthma) and seasonal allergies, such as sneezing, itchiness and a blocked or runny nose (allergic rhinitis).

Montelukast is sometimes given to people without asthma to treat hives (urticaria) that last for a long time (more than 6 weeks).

• Montelukast helps stop your airways from narrowing (caused by inflammation). This makes breathing easier and prevents asthma attacks.
• Most people take montelukast once a day in the evening.
• If you take it for asthma, it's important to take it even when you have no symptoms.
• Montelukast is used alongside your inhalers or other asthma medicine.
• Some common side effects include headaches and feeling or being sick.

Montelukast can be taken by adults and children from 6 months of age.

Montelukast is not suitable for people with certain health problems.

Check with your doctor before taking montelukast if:

• you have had an allergic reaction to montelukast or any other medicine in the past
• you have a rare hereditary problem of galactose intolerance (including Lapp lactase deficiency or glucose-galactose malabsorption)

Always follow your doctor's instructions about how and when to take montelukast.

Dosage

Most people take montelukast once a day in the evening to prevent asthma or allergy symptoms. However, if exercise makes your asthma worse, your doctor might tell you to take montelukast 2 hours before you exercise. Never take more than 1 dose a day.

The usual dose for:

• adults and children aged 15 years and older – one 10mg tablet
• children aged 6 to 14 years – one 5mg chewable tablet
• children from 6 months old to 5 years – 4mg (this can be granules or as a chewable tablet)

How to take non-chewable tablets

You can take montelukast non-chewable tablets with or without food

Swallow tablets whole with water, juice or milk. Do not chew these tablets.

How to take chewable tablets

It's important to take chewable tablets at least 1 hour before food, or 2 hours after food. This is so the medicine is absorbed into your body properly.

Chewable tablets can be chewed or sucked. You or your child can have a drink of water or squash afterwards.

How to give granules to a child

Montelukast granules come in a sachet with 4mg of granules inside (one dose). They can be put directly on your child's tongue. You can also mix the granules with a spoonful of cold, soft food, such as yoghurt or ice-cream.

Make sure your child takes the whole dose immediately (or within 15 minutes).

It's important to not dissolve the granules in a drink. You can give your child a drink afterwards.

What if I forget to take it?

If you or your child misses a dose of montelukast, skip the missed dose and take your next dose the following day at the usual time.

Do not take a double dose to make up for a forgotten dose.

If you forget doses often, it may help to set an alarm to remind you. You could also ask a pharmacist for advice on other ways to help you remember to take your medicine.

What if I take too much?

If you need to go to hospital, do not drive yourself. Get someone else to drive you or call for an ambulance. Find your nearest A&E.

Take the montelukast packet or leaflet inside it plus any remaining medicine with you.

Like all medicines, montelukast can cause side effects, although not everyone gets them.

Common side effects

These side effects can affect more than 1 in 100 people.

Talk to a pharmacist or doctor if these side effects bother you or do not go away:

• diarrhoea
• high temperature
• headaches
• stomach ache, feeling or being sick (nausea or vomiting)
• a mild rash

Serious side effects

Contact a doctor immediately if:

• you notice mood changes and you become depressed, aggressive or you're thinking of harming yourself
• you see things which are not there (hallucinations)
• you're finding it harder than usual to concentrate or remember things
• your speech changes or you start stuttering
• you have shaking or trembling in any part of your body
• you have an unusual or fast heartbeat
• you get yellow skin or the whites of your eyes become yellow – this could be a sign of liver problems

Serious allergic reaction

It is possible to have a serious allergic reaction (anaphylaxis) to montelukast.

These are not all the side effects of montelukast. For a full list see the leaflet inside your medicines packet.

What to do about:

• diarrhoea – drink plenty of fluids, such as water or squash to prevent dehydration. Signs of dehydration include peeing less than usual or having dark, strong-smelling pee. Do not take any medicines to treat diarrhoea without speaking to a pharmacist or doctor.
• high temperature – paracetamol will help to bring the temperature down. Drink plenty of fluids. See your doctor if it lasts for more than a few days.
• headaches – make sure you rest and drink plenty of fluids. Do not drink too much alcohol. Ask your pharmacist to recommend a painkiller. Headaches should usually go away after the first week of taking montelukast. Talk to your doctor if headaches last longer than a week or are severe.
• stomach ache, feeling or being sick – stick to simple meals and do not eat rich or spicy food. If you're being sick, try having small, frequent sips of water or squash to avoid dehydration. Do not take any other medicines to treat vomiting without speaking to a pharmacist or doctor. Putting a heat pad or covered hot water bottle on your stomach may also help
• a mild rash – it may help to take an antihistamine, which you can buy from a pharmacy. Check with the pharmacist to see what type is right for you. If the rash gets worse, or does not get better after a week, speak to your doctor.

Montelukast and pregnancy

It's important for you and your baby to stay well when you're pregnant. If montelukast stops your asthma getting worse, you can keep taking it, even when you are pregnant.

The risks of having serious asthma attacks during pregnancy are much worse than the risks of using montelukast. Asthma attacks can prevent your unborn baby from getting enough oxygen.

Speak to your doctor if you become pregnant while you are taking montelukast.

Montelukast and breastfeeding

If your doctor or health visitor says your baby is healthy, you can take montelukast while you're breastfeeding.

Montelukast passes into breast milk in small amounts. The benefits of the medicine are greater than the small risk of side effects in your baby.

If you notice that your baby is not feeding as well as usual, seems unusually sleep, or if you have any other concerns about your baby, talk to a health visitor or doctor immediately.

Find out more about how montelukast can affect you and your baby during pregnancy on the Best Use of Medicines in Pregnancy (BUMPS) website.

Tell your doctor if you are taking any of the following medicines:

• epilepsy medicines such as phenobarbital and phenytoin
• rifampicin (for tuberculosis)
• gemfibrozil (for high-cholesterol)

It's usually safe to take everyday painkillers with montelukast. However, do not take non-steroidal anti-inflammatory drugs (NSAIDs) such as aspirin or ibuprofen if they have ever made your asthma symptoms worse.

Mixing montelukast with herbal remedies and supplements

There's very little information about taking herbal medicines and supplements with montelukast. Ask a pharmacist for advice.