Your child needs to take the medicine called montelukast (say: mon-te-LOO-kast). This information sheet explains what montelukast does, how to give it, and what side effects or problems your child may have when he or she takes this medicine.

What is montelukast?

Montelukast is a medicine that improves asthma symptoms and helps prevent asthma attacks. It is also used to prevent breathing difficulties caused by exercise. Your child may use montelukast to treat seasonal allergies. It is not for use in an acute asthma attack. 

Montelukast works by blocking the action of substances in the body that cause the symptoms of asthma and allergies.

You may hear montelukast called by its brand name, Singulair®. Montelukast comes as a tablet, a chewable tablet, and granules to be taken by mouth.

Before giving montelukast to your child…

Your child should not take montelukast if he or she has had any unusual or allergic reaction to montelukast.

Talk with your doctor or pharmacist if your child has any of the following conditions. Precautions may need to be taken with this medicine if your child has:

  • phenylketonuria (PKU): chewable tablets contain phenylalanine
  • liver disease

How should you give your child montelukast?

Follow these instructions when giving your child montelukast:

  • Give your child this medicine exactly as your child’s doctor or pharmacist tells you to.
  • Give your child this medicine at the same time every evening, unless your child’s doctor tells you otherwise.
  • Montelukast may be given with or without food.
  • Continue to give montelukast to your child even when he/she is not having asthma symptoms. Do not stop giving your child this medicine unless your child’s doctor tells you to.

If your child is taking regular montelukast tablets, they should be swallowed whole. Do not break, crush, or chew them.

If your child is taking the chewable tablets, they should be chewed before your child swallows them.

If your child is taking the oral granules, do not open the packet until ready to use. There are several ways that you can give the granules to your child. Choose the one that works best for you and your child. You may either:

  • Pour all of the granules directly from the packet into your child's mouth to be swallowed, OR
  • Put the granules directly on a spoon, then into the child's mouth, OR
  • Mix all of the contents of the granules into a spoonful of cold or room temperature soft food such as baby formula, applesauce, ice-cream. You should not mix the granules with any other foods or liquids, but your child may drink any liquid right after he or she takes the granules. Be sure your child takes the entire spoonful of the granules/food mixture immediately (within 15 minutes).

Never store any granules/food mixture for use at a later time.

What should you do if your child misses a dose of montelukast?

  • Give the missed dose as soon as you remember.
  • If it is almost time for the next dose, skip the missed dose. Give the next dose at the regular time.
  • Do not give your child two doses to make up for one missed dose.

How long does montelukast take to work?

It usually takes one day for this medicine to work.

What are the possible side effects of montelukast?

Your child may have some of these side effects while he or she takes montelukast. Check with your child's doctor if your child continues to have any of these side effects, and they do not go away, or they bother your child:

  • headache, dizziness
  • upset stomach: either watery bowel movements, nausea, or stomach pain
  • tiredness, weakness
  • sore throat, cough
  • unusual dreams, trouble sleeping
  • runny or stuffy nose

Most of the following side effects are not common, but they may be a sign of a serious problem.   

Call your child's doctor right away or take your child to the Emergency Department if your child has any of these side effects:

  • signs of a severe allergic reaction: difficulty breathing or swallowing; swelling of the face, lips, tongue, or throat; itching, rash, or hives
  • signs of liver problems: severe nausea or vomiting, abdominal pain, yellowing of the skin and eyes
  • combination of the following symptoms that are persistent or worsening: flu-like symptoms, pins and needles sensation or numbness in the arms or legs, pain and swelling of the sinuses, joint pain

What safety measures should you take when your child is using montelukast?

Do not use montelukast to treat a sudden attack of asthma symptoms. Talk to your child’s doctor about how to treat symptoms of an asthma attack. If your child’s asthma symptoms get worse or your child has asthma attacks more often, be sure to call your doctor.

Check with your child’s doctor or pharmacist before you give your child any other medicines, even medicines that you can buy without a doctor’s order (prescription).

There are some medicines that should not be taken together with montelukast, or in some cases, the dose of montelukast or the other medicine may need to be adjusted. It is important that you tell your doctor and pharmacist if your child takes any other medications, including:

If your child has phenylketonuria (PKU), do not use the chewable tablet form of montelukast. The regular tablets may be used. 

What other important information should you know about montelukast?

Make sure you always have enough montelukast to last through weekends, holidays, and vacations. Call your pharmacy at least 2 days before your child runs out of medicine to order refills.

Keep montelukast at room temperature in a cool, dry place away from sunlight. Do not store it in the bathroom or kitchen.

Do not share your child’s medicine with others. Do not give anyone else’s medicine to your child.

Do not keep any medicines that are out of date. Check with your pharmacist about the best way to throw away outdated or leftover medicines.

Keep a list of all medications your child is on and show the list to the doctor or pharmacist.

Keep montelukast out of your child’s sight and reach and locked up in a safe place. If your child takes too much montelukast, call the Ontario Poison Centre at one of these numbers. These calls are free.

  • Call 416-813-5900 if you live in Toronto.
  • Call 1-800-268-9017 if you live somewhere else in Ontario.
  • If you live outside of Ontario, call your local Poison Information Centre.

Disclaimer: The information in this Family Med-aid is accurate at the time of printing. It provides a summary of information about montelukast and does not contain all possible information about this medicine. Not all side effects are listed. If you have any questions or want more information about montelukast, speak to your healthcare provider. 

Jennifer Drynan-Arsenault, BSc, RPh, ACPR