Singulair for allergies: what is it and how does it work?

Reviewed by Chimene Richa, MD, 

Written by Michael Martin 

Reviewed by Chimene Richa, MD, 

Written by Michael Martin 

last updated: Jul 02, 2021

3 min read

Many people are familiar with over-the-counter allergy medications like Claritin and Allegra. However, some people need something stronger, including prescription drugs like Singulair for their allergies. But before you start this drug, here’s some information about Singulair and how it works. 


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What is Singulair?

Singulair, the brand name of montelukast sodium, is made by the pharmaceutical company Merck and is only available by prescription. It helps people with allergy or asthma symptoms to breathe easier. 

Singulair is approved by the U.S. Food and Drug Administration (FDA) to treat the following conditions (FDA, 2020-a):

  • Asthma, a long-term health condition that involves inflammation and narrowing in your lung airways, leading to wheezing, difficulty breathing, chest tightness, and coughing

  • Exercise-induced bronchoconstriction (EIB), or tightening of the airways during exercise

  • Perennial allergic rhinitis or seasonal allergic rhinitis (hay fever) symptoms, including sneezing, nasal congestion, runny nose, and more

While the FDA approves Singulair for the treatment of asthma, healthcare providers sometimes use it for “off-label” uses. Off-label means that a drug is being used to treat a condition other than its FDA-approved ones. Off-label uses of Singulair include (UptoDate, n.d.):

  • Lung problems due to aspirin

  • Hypersensitivity reactions

  • Prevent chemotherapy reactions

  • Hives (urticaria)

Singulair dosing

Singulair comes in an oral 10 mg tablet and 4 mg or 5 mg chewable tablet forms. The chewable form contains aspartame, which is made from phenylalanine, an amino acid. People with phenylketonuria (PKU) cannot break down phenylalanine and should talk with their healthcare provider before starting Singulair (FDA, 2020-a).

There are also oral granules that you can take by mixing them with a spoonful of room temperature applesauce or ice cream (or in baby formula for children over 6–12 months of age (UptoDate, n.d.)

The typical Singulair dose is 10 mg, usually taken once per day. 

How does Singulair work?

Singulair belongs to a group of medications called leukotriene receptor antagonists (LTRA). When you encounter an allergen (like pollen, etc.) that you are allergic to, your immune system releases chemicals called leukotrienes. 

Leukotrienes cause the smooth muscle of your airways to constrict, encourage airway swelling, and lead to other physical changes that contribute to the symptoms of allergic asthma and allergic rhinitis. LTRA medications like Singulair block leukotriene receptors on the cells, which can help prevent allergic symptoms (Wermuth, 2021).

OC Singulair for allergies: what is it and how does it work? image 6b6d2d2f-c307-47bd-bdb5-8b13d44d66c9

People may also use Singulair before they work out to prevent breathing problems during exercise, known as exercise-induced bronchospasm or bronchoconstriction (tightening of the airways during exercise). 

Singulair can help people who experience bronchospasms or asthma reduce the number of times they have to use their quick-relief asthma medication or a rescue inhaler. Singulair is an asthma controller medicine or preventer medicine because people who use it need to take it regularly, not just when an acute asthma attack strikes (Wermuth, 2021).

Possible side effects and risks of Singulair

Singular carries a boxed warning from the FDA (the most serious warning they apply to medications) because it may cause serious side effects like agitation, disorientation, depression, trouble sleeping, and suicidal thoughts and behavior (including suicide). Families and healthcare providers should be on the lookout for these changes. Consider using Singulair only after other allergic rhinitis treatments have been tried. Discuss the risks and benefits of starting Singulair with your healthcare provider (FDA, 2020-b). 

Singulair may cause side effects, and in some people, the side effects can be serious. Some of the most common side effects include upper respiratory infections, flu, fever, headache, sore throat, cough, and stomach pain (FDA, 2020-a). 

Additional (but less common) side effects include an increased tendency to bleed, low blood platelet count, allergic reactions, dizziness, drowsiness, numbness or pins and needles, seizures, and heart palpitations. People may also experience heartburn or indigestion, vomiting, hepatitis, bruising, and/or skin reactions. In some cases, people may have pain in their joints or muscles, muscle cramps, tiredness, and swelling, and in children, bed-wetting may occur.

If you experience any adverse effects while taking Singulair, it’s important to talk to your healthcare provider. People who have asthma and experience worsening symptoms when they take aspirin should avoid aspirin and non-steroidal anti-inflammatory drugs (NSAIDs) while taking Singulair. 

People who are allergic to aspirin or have a condition called phenylketonuria should talk to their healthcare providers to get medical advice about the possible pros and cons of taking Singulair. Tell your provider about any other medical conditions you may have. Women who are pregnant or plan to become pregnant should also discuss using Singulair with their healthcare provider. Lastly, while there is little risk to the baby if you are breastfeeding, know that Singulair is present in breast milk. Discuss this with your healthcare provider. 

There are a few drug interactions to mention. Taking Singulair with gemfibrozil may increase your blood concentration of Singulair. Conversely, drugs like lumacaftor and ivacaftor may lower Singulair levels. 


If you have any medical questions or concerns, please talk to your healthcare provider. The articles on Health Guide are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis, or treatment.

How we reviewed this article

Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

Current version

July 02, 2021

Written by

Michael Martin

Fact checked by

Chimene Richa, MD

About the medical reviewer

Dr. Richa is a board-certified Ophthalmologist and medical writer for Ro.