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Singulair: 7 things you should know

Medically reviewed by Carmen Pope, BPharm. Last updated on Nov 13, 2023.

1. How it works

  • Singulair is a brand (trade) name for montelukast which may be used for the treatment of asthma or allergic rhinitis.
  • Singulair (montelukast) works by inhibiting specific receptors in the airways called leukotriene receptors. These receptors are affected by substances released during inflammation and following exposure to an allergen. By blocking these receptors, montelukast relieves airway edema, relaxes smooth muscle, and dampens the inflammatory response.
  • Singulair belongs to the class of medicines known as oral leukotriene receptor antagonists.

2. Upsides

  • Used for the maintenance treatment of asthma in adults and children aged older than 12 months.
  • May also be used to treat exercise-induced bronchospasm (EIB) in adults and children aged six years and older. A single dose should be taken at least two hours before exercise.
  • May also be given as a preventative for seasonal allergic rhinitis (hay fever) in adults and children aged two years of age and older, and perennial allergic rhinitis in adults and children aged six months and older.
  • Available as tablets, chewable tablets, and oral granules. Granules may be dissolved in baby formula or breast milk for administration to children older than 12 months.
  • No dosage adjustment is necessary for people with kidney disease or mild-to-moderate liver disease.
  • Taken once a day.
  • May be taken with or without food.
  • Singulair is available as a generic under the name montelukast.

3. Downsides

If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:

  • A headache, abdominal pain, influenza, dyspepsia, cough, an increased bleeding tendency, a rash, and laboratory test disturbances.
  • May cause psychiatric-type effects including agitation, aggressive behavior, anxiety, depression, abnormal dreams, and hallucinations. These have been reported in people of all ages taking Singulair.
  • May cause dizziness or drowsiness and affect a person's ability to drive and operate machinery.
  • Not a treatment for an acute asthma attack. Albuterol or another short-acting bronchodilator should be used instead.
  • May not be suitable for some people including those with liver disease or a history of reaction to Singulair or other foods or dyes.
  • Singulair may interact with some other medications including carbamazepine, phenytoin, phenobarbital, rifampin, repaglinide, rosiglitazone, and paclitaxel.
  • Although no association between Singulair use during pregnancy and birth defects has been reported, weigh up the benefits versus risks before using during pregnancy. Singulair has been shown to pass into breastmilk and data available do not suggest any significant risk of adverse effects to the infant.

Note: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. View complete list of side effects

4. Bottom Line

  • Singulair is used in addition to other treatments for the maintenance treatment of asthma. It does not relieve acute attacks and may cause neuropsychiatric effects in a small number of people.

5. Tips

  • May be administered with or without food. Available as tablets, chewable tablets, and oral granules. The granules can be administered directly into the mouth or dissolved in a teaspoonful of breast milk or formula, or soft food such as applesauce, carrots, rice, or ice cream. Once the packet is opened, the contents should be taken within 15 minutes. Discard any unused portion.
  • Take once daily in the evening when used as a preventative treatment for asthma. Take Singulair daily as prescribed, even if you have no symptoms of asthma. Do not take another dose of Singulair within 24 hours of a previous dose. Do not increase or decrease the dose of Singulair without your doctor's permission and continue to take all other asthma medications as prescribed.
  • Take at least two hours before exercise when given to prevent exercise-induced bronchoconstriction. However, if you have already taken a dose of Singulair in the previous 24 hours, do not take another dose.
  • When given for allergic rhinitis, only a single dose should be taken daily but it may be dosed morning or evening depending on patient preference.
  • If you miss a dose, take it as soon as possible. But if it is almost time for your next dose, just skip that dose. Do not double up on doses.
  • Take exactly as prescribed when given for asthma, even if you are asymptomatic. Continue taking as prescribed even during an acute asthma attack, although Singulair will not treat an acute attack.
  • You should talk with your doctor beforehand about what to do if you have an acute asthma attack. This should include taking your short-acting bronchodilator medicine (commonly albuterol) as prescribed. Singulair is not for use during an acute attack. Talk to your doctor if you regularly need to take more of your acute asthma treatment.
  • Notify your doctor if you experience any neuropsychiatric effects (such as aggression, anxiety, depression, tics, thoughts of suicide, or hallucinations) while taking Singulair. Also, tell your doctor if you develop any symptoms of an allergic reaction including a rash or breathing problems; or side effects such as an abnormal heartbeat, unusual bruising, yellowing of the skin or eye, trouble sleeping or tingling or twitching in your fingers and toes.
  • Avoid driving or operating machinery if Singulair makes you drowsy or dizzy.
  • If you know you are sensitive to aspirin or other NSAIDs, continue to avoid these while taking Singulair.
  • Phenylketonurics note: The 4mg and 5mg chewable tablets contain phenylalanine.
  • Tell your doctor if you are breastfeeding, pregnant, or intending to become pregnant because they will need to discuss the risks versus benefits of using Singulair while pregnant or breastfeeding.

6. Response and effectiveness

  • Peak concentrations of Singulair are reached within three to four hours. It may take several weeks before improvements in breathing measurements, such as forced expiratory volume [FEV]) are noted.

7. Interactions

Medicines that interact with Singulair may either decrease its effect, affect how long it works, increase side effects, or have less of an effect when taken with Singulair. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.

Common medications that may interact with Singulair include:

  • anticonvulsants, such as carbamazepine, Divalproex, fosphenytoin, or phenytoin
  • antifungals, such as fluconazole, miconazole, or voriconazole
  • echinacea
  • fibrates, such as gemfibrozil
  • fluvoxamine
  • heart medications, such as amiodarone
  • HIV medications, such as efavirenz
  • isoniazid
  • metronidazole
  • nafcillin
  • phenobarbital
  • rifampin
  • St. John's wort
  • sulfamethoxazole
  • tamoxifen
  • trimethoprim
  • zafirlukast.

Note that this list is not all-inclusive and includes only common medications that may interact with Singulair. You should refer to the prescribing information for Singulair for a complete list of interactions.


Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use Singulair only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Copyright 1996-2023 Revision date: November 13, 2023.