What is Singulair?

Singulair, also known as montelukast, is a prescription medication used in the treatment of asthma and seasonal allergies. It belongs to a class of drugs called leukotriene receptor antagonists. Singulair works by blocking certain chemicals called leukotrienes, which are responsible for causing inflammation and constriction of airways. By inhibiting leukotrienes, Singulair helps improve breathing, reduce asthma symptoms, and alleviate allergy symptoms such as sneezing and runny nose. It is typically taken orally, once daily, and the dosage may vary based on age and condition being treated. Singulair is often used as part of a comprehensive treatment plan that may include other asthma or allergy medications. Regular consultation with a healthcare professional is important for personalized guidance, potential side effects, and monitoring treatment effectiveness.

Singulair (Montelukast)

Prescription Required.

Product of Canada.

Shipped from Canada.

Prescription Required.Product of Canada.Shipped from Canada.

What is Singulair?

Singulair, also known by its generic name, Montelukast, belongs to a group of drugs named leukotriene receptor antagonists and was approved by the U.S. Food and Drug Administration (FDA) in 1998. It is used in the treatment of asthma symptoms.

It is prescribed for adults and children who are at least a year old. Adults, and children aged at least 6, who are looking to prevent exercise-induced asthma (exercise-induced bronchoconstriction) are prescribed Singulair. Singulair is also prescribed for adults and children aged at least 2 who are suffering from seasonal allergies or to adults and children aged at least 6 months who suffer from allergies throughout the year.

Singulair can be taken alone or combined with other asthma medicines and normally begins working within a day.

How does it work?

Singulair works by preventing asthma symptoms and helping to manage seasonal allergy symptoms (seasonal allergic rhinitis or hay fever). It blocks the results of leukotrienes, a substance naturally produced by the body. The body produces leukotrienes in response to triggers that affect the lungs’ airways, causing them to narrow and swell.

Once an asthma attack has begun, Singulair should not be used to relieve it. It should instead be used to prevent attacks and manage asthma. Instead of using Singulair to relieve the effects of an asthma attack, patients should have fast-acting medication to relieve the effects of asthma.

Appearance & ingredients

Singulair comes in a variety of forms and doses.

The 10 mg tablets are beige, coated, and square-shaped with rounded edges. On one side the code “MSD 117” is visible while the other side features “SINGULAIR”. Each one contains 10.4 mg of montelukast sodium. Its other ingredients consist of:

  • croscarmellose sodium
  • hydroxypropyl cellulose
  • lactose monohydrate
  • magnesium stearate
  • microcrystalline cellulose
  • film-coating:
    • carnauba wax
    • hydroxypropyl cellulose
    • hydroxypropyl methylcellulose
    • red ferric oxide
    • titanium dioxide
    • yellow ferric oxide

The chewable tablets are pink in color and are available in 4 mg and 5 mg doses. The 4 mg tablet features the code “MSD 711” on one side and the 5 mg tablet features “MSD 275”. For both doses, their other sides read: “SINGULAIR”. The 4 mg tablets are oval and contain 4.2 mg of montelukast sodium, while the 5 mg tablets are round and contain 5.2 mg of montelukast sodium. Each tablet’s nonmedicinal ingredients include:

  • aspartame
  • cherry flavor
  • croscarmellose sodium
  • hydroxypropyl cellulose
  • magnesium stearate
  • mannitol
  • microcrystalline cellulose
  • red ferric oxide

Singulair also comes as packets of white and coarse granules with each foil packet containing 4 mg of free-flowing homogeneous solid. Each packet contains 4.2 mg of montelukast sodium. The nonmedicinal ingredients include:

  • hydroxypropyl cellulose
  • magnesium stearate
  • mannitol


For adults and children aged 15 and over who are dealing with asthma, the recommended dose is a single 10 mg tablet once in the evening.

A chewable 5 mg dose is recommended for children aged between 6 and 14 once in the evening.

For children aged between 2 and 5, a chewable 4 mg tablet is the recommended dose once in the evening or a 4 mg packet of granules.

The granules should be taken orally, directly in the mouth, or mixed with soft food at room temperature, such as apple sauce. The foil packet should be left sealed until it is ready for use. Once the packet is opened, the oral granules should be taken within 15 minutes. The oral granules mixed with food should not be stored for later use. The granules should not be mixed with liquids.


If you think you or anyone else may have had an overdose of Singulair, you should seek emergency medical attention.

Side effects

If you are concerned about experiencing side effects from taking Singulair, you should talk it over with your doctor and weigh up the risks against the benefits. Many of these side effects may disappear over time or can be managed. Your pharmacist should be able to make recommendations for managing these side effects, however, you should contact your doctor if they become severe or significantly uncomfortable.

The side effects of Singulair are not experienced by everyone who takes it, but at least 1% of people taking this medication have experienced those listed below.

  • abdominal or stomach pain
  • abnormal dreams
  • bedwetting (for children)
  • diarrhea
  • dizziness
  • drowsiness
  • fatigue
  • fever
  • headache
  • muscle aches or cramps
  • scaly and itchy skin
  • skin rash
  • symptoms of a cold (i.e., sore throat, runny nose, nasal congestion)
  • thirst
  • trouble sleeping
  • weakness or unusual tiredness

More serious side effects

These serious side effects are rare but can cause serious issues if they are not addressed. If you experience any of these, you should see your doctor as soon as possible.

  • aggressive behavior, such as a bad temper
  • asthma symptoms
  • behavior changes, such as:
    • anxiety
    • irritability
    • aggressiveness
    • hostility
  • disorientation
  • hyperactivity
  • memory problems
  • rapid or irregular heartbeat
  • red lumps under the skin, mostly on the shins
  • respiratory tract infection
  • restlessness
  • hallucinations
  • signs of clotting problems, such as:
    • unusual nosebleeds
    • bruising
    • blood in urine
    • coughing blood
    • bleeding gums
    • cuts that won’t stop bleeding
  • signs of depression, such as:
    • poor concentration
    • changes in weight
    • changes in sleep
    • decreased interest in activities
    • thoughts of suicide
  • signs of liver problems, such as
  • nausea
  • vomiting
  • diarrhea
  • loss of appetite
  • weight loss
  • jaundiced skin or yellowing whites of the eyes
  • dark urine, pale stools
  • sleepwalking
  • swelling
  • tremor
  • trouble paying attention
  • uncontrolled muscle movement

Side effects requiring urgent medical attention

If you experience any of the following side effects, discontinue the treatment and immediately seek the attention of a medical professional.

  • breathing problems that worsen
  • seizures
  • signs of a severe allergic reaction, such as:
    • abdominal cramps
    • difficulty breathing
    • nausea and vomiting
    • swelling of the face and throat
  • signs of a severe skin reaction, such as:
    • blistering
    • peeling
    • a large rash
    • a fast-spreading rash
    • uncomfortable rash with fever
  • symptoms of Churg-Strauss syndrome, such as:
    • persistent or worsening flu-like symptoms
    • a rash
    • pins and needles
    • numbness of the arms or legs
    • joint pain
    • severe sinusitis
  • thoughts of self-harm or suicide

Side effects other than those listed above are possible. If any symptoms develop that worry you whilst taking Singulair, you should discuss them with your doctor.

Warnings & Precautions

Always check the ingredients of any medication you take for anything you may be allergic to. You should not take Singulair if you are allergic to any of the ingredients in it.

Make sure your doctor is aware of any medical conditions or allergies you have as this may impact whether or not they recommend Singulair for you.

Controlling asthma and asthma attacks

Singulair has not been found to treat asthma attacks, so you should not use it for that. Instead, you should always have your asthma medication ready for an acute attack.

You should not suddenly stop using Singulair without discussing it with your doctor, even if you think you have your asthma under control. You need to take it daily in order for it to have a positive impact unless your doctor has recommended otherwise.

If you do not believe your asthma symptoms are getting better, or feel they are worsening, whilst using Singulair, you should discuss it with your doctor. If you notice that acetylsalicylic acid (ASA) makes your asthma worse, you should not take ASA or any nonsteroidal anti-inflammatory medications (NSAIDs), such as ibuprofen, ketoprofen, or naproxen. If you find that exercise makes your asthma worse, you should carry on taking the medications before exercise as prescribed by your doctor.

Changes in behavior

Changed behavior has been reported in people who have been taking Singulair. If you experience or notice any of the following you should contact your doctor as soon as you can.

  • aggression
  • hostility
  • anxiousness
  • disorientation
  • decreased memory
  • disturbed sleep
  • suicidal thoughts


Before you take Singulair, you should let your doctor know if you are depressed or have a history of depression as mood swings and depression symptoms have been connected with Singulair. Your doctor should let you know how it might impact your condition, how the dosing of the medication and its effectiveness may be affected by your condition, and whether you may need to be monitored. The symptoms of depression may include:

  • poor concentration
  • changes in weight
  • changes in sleep
  • decreased interest in activities

If you notice any of these in yourself or anyone else who is taking Singulair, you should get in touch with your doctor as soon as you can.


The chewable form of Singulair contains aspartame which contains phenylalanine. Patients with phenylketonuria cannot break down phenylalanine and their bodies are unable to expel it. If you have phenylketonuria, you should discuss alternatives with your doctor.


Singulair can build up in the body, resulting in side effects if you suffer from liver disease or compromised liver function. It is not yet known how safe Singulair is for people with liver problems, but you should discuss it with your doctor if your liver function is compromised. Your doctor should let you know how taking Singulair might impact your condition, how the dosing of the medication and its effectiveness may be affected by your condition, and whether you may need to be monitored. If you notice any symptoms of liver issues, you should let your doctor know as soon as possible. The symptoms include:

  • fatigue
  • feeling unwell
  • loss of appetite
  • nausea
  • jaundiced skin or yellowing whites of the eyes
  • dark urine
  • pale stools
  • abdominal pain or swelling
  • itchy skin

Pregnancy, breastfeeding, and children

You should not use Singulair during pregnancy unless you and your doctor have considered the benefits and risks. You should seek your doctor’s guidance as soon as you become aware that you are pregnant if you become pregnant while using Singulair. It is not known whether Singulair can be passed from mother to baby through breast milk. However, there is a chance that it can affect your baby if you breastfeed whilst using Singulair. You should consult your doctor about whether you should carry on breastfeeding if you are using Singulair.

Singulair has not yet been established as safe or effective for children under the age of 2.


Singulair may interact with:

  • Gemfibrozil
  • Lumacaftor and ivacaftor

Singulair is not known to interact with any foods.

Frequently Asked Questions

Singulair may be prescribed for conditions other than those mentioned above. If you do not know why your doctor has prescribed it for you, you should ask them. It is important not to stop taking Singulair without discussing it with your doctor.

It’s important that you do not give your prescribed Singulair to anyone else. Even if they have the same symptoms as you, it can be harmful to them if they have not been prescribed it.

Many things might affect the dose you are prescribed. Your weight, other medical factors, and other medications you are on can have an impact. Do not take anything other than the dose you have been given by your doctor.

It is vital that you take Singulair exactly as your doctor has prescribed, so if you miss a dose you should seek guidance from your doctor. However, do not attempt to give yourself two doses to make up for the one you missed.

An interaction does not necessarily mean you need to stop taking one. You should speak with your doctor and they will be able to help you manage your medications.

It depends on the situation, but your doctor might suggest:

  • you stop taking the medication
  • you change to a different medication
  • change your dosage of Singulair, the other medication, or both
  • leave things as they are.

Other medications may interact with Singulair, you should inform your doctor of all prescription, over-the-counter and herbal medicines. They should be made aware of any supplements you’re taking. You should also tell your doctor if you smoke, use street drugs or consume caffeine products.

Try to avoid activities or situations that could initiate an asthma attack. Try not to take aspirin or other nonsteroidal anti-inflammatory drugs (NSAIDs), such as:

  • ibuprofen
  • naproxen
  • celecoxib
  • diclofenac
  • indomethacin
  • meloxicam and others

Singulair normally stays in the system for roughly 30 hours.

Before taking Singulair, you should let your healthcare provider know if you:

  • are allergic to aspirin
  • have phenylketonuria
  • are pregnant or breastfeeding
  • are taking any other medicines, vitamins, and herbal supplements.

Singulair should be stored at 59°F to 86°F in the container it comes in, in a dry place that is away from light.

Singulair tablets normally begin to work within 2 hours of the person taking their dose. Otherwise, it begins working within a day.

Sleep problems have been reported by people using Singulair. These problems may include:

  • insomnia
  • unusual dreams
  • sleepwalking
  • talking in one’s sleep

Some people may have an allergic reaction. Symptoms of a mild allergic reaction include:

  • a rash
  • itchiness
  • temporary warmth or redness

Symptoms of a severe allergic reaction may include:

  • swelling under the skin, swollen eyelids, lips, hands, feet
  • swollen tongue, mouth, or throat
  • difficulty breathing

If you have an allergic reaction to Singulair, you should contact your doctor as soon as possible.

If your doctor and you are satisfied that Singulair is safe and effective for you, it will be a long-term treatment.