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Singulair side effects and how to avoid them

Singulair side effects include flu-like symptoms, stomach upset, and increased risk of infection

Common Singulair side effects | Increased risk of infection | Stomach upset | Serious side effects | Mental health problems | Withdrawal | How long do side effects last? | Warnings | Interactions | How to avoid side effects

Singulair (brand name of montelukast) is an FDA-approved prescription medication used for the treatment and prevention of asthma and treatment of allergic rhinitis (hay fever) symptoms including runny nose and sneezing. Singulair can also be used to prevent exercise-induced bronchoconstriction. The medication should be taken daily to work at its best, but it can also be taken as needed for exercise-induced bronchoconstriction. It is not intended as a rescue asthma medication and will not treat sudden asthma attacks. Those with asthma should talk to their healthcare provider about using Singulair along with a rescue inhaler.

In general, Singulair is well-tolerated for most people. Singulair could come with side effects, which include headaches, fever or flu-like symptoms, and stomach pain. Some side effects can be serious and should be talked about with a doctor before taking Singulair.

The medication works well for many asthma patients, but it is not a cure. In studies, Singulair has been found to increase the FEV₁, forced expiratory volume, of patients with asthma. This means these patients experienced improved airflow and improvements in their breathing. And in studies for allergic rhinitis, Singulair has been found to show a significant reduction in daytime nasal symptoms for these patients. These symptoms include nasal congestion, runny nose, nasal itching, and sneezing. 

RELATED: Are you using the best medicine for seasonal allergic rhinitis?

Common side effects of Singulair

There is always a risk of side effects when taking medication, and this remains true with Singulair. Commonly experienced side effects include:

  • Headache
  • Fever
  • Flu-like symptoms
  • Stomach pain
  • Sore throat
  • Cough
  • Diarrhea
  • Nausea
  • Ear infection
  • Indigestion
  • Rash
  • Hives
  • Sinus infection
  • Sleep disturbances
  • Anxiety
  • Irritability
  • Restlessness
  • Tremors

Increased risk of infection

Singulair could increase a person’s chance of an upper respiratory infection, flu-like symptoms, sinus infection, or ear infection. This medication works to prevent the inflammatory process of leukotrienes which are inflammatory chemicals in the body that are often released when triggered by an allergen. Because Singulair works on this chemical involved in the body’s immune pathway, there is the possibility for interference in the body’s immune response.

Signs of an upper respiratory infection include a sore throat, stuffy nose, cough, painful swallowing, and sneezing. Signs of an ear infection include ear pain, fever, hearing difficulties, and fluid drainage from the ears. If an infection is suspected, it’s best for patients to contact their doctors for treatment. It’s important for those taking Singulair to be aware of the signs of infection.

Stomach upset

Some people taking Singulair may experience stomach upset including stomach pain, nausea, indigestion, or diarrhea. There are a few strategies patients can try to lessen stomach upset while taking Singulair. Since Singulair can be taken with or without food, eating a snack with the dose of Singulair may help to settle the stomach and lessen upset. Another strategy is taking the Singulair dose as close to bedtime as possible. The goal is for patients to rest in bed and fall asleep before nausea develops.

Serious side effects of Singulair

Serious side effects of Singulair include:

  • Neuropsychiatric disorders (aggressive behaviors, depression, hallucinations, insomnia, suicidal thoughts)
  • Serious allergic reaction
  • Eosinophil-related inflammation (hepatic eosinophilic infiltration)
  • Pulmonary eosinophilia
  • Churg-Strauss syndrome (a disorder characterized by blood vessel inflammation and reduced blood flow to organs/tissues)
  • Thrombocytopenia (low platelet count)

Mental health problems

Behavior and mood-related changes are known serious side effects of taking Singulair. These changes in behavior may lead to anxiety-like feelings. Other mood-related symptoms that have been reported in patients taking Singulair include agitation, aggressiveness, bad dreams, hallucinations, trouble sleeping, tremors, memory problems, obsessive-compulsive disorder, depression, and suicidal thoughts. Patients should notify their healthcare provider if they notice any changes in their behavior or mood while taking Singulair. For free and confidential support, there is the National Suicide Prevention Lifeline: 1-800-273-8255.

In 2020, the Food and Drug Administration put out a boxed warning pertaining to the serious risk of mental health side effects of Singulair based on reports they have received. This decision was made based on the FDA’s review of many case reports and the results of their observational study. Patients and their healthcare providers should discuss the risks and benefits before taking Singulair. Those who have a history of mental illness may need to avoid taking this medication. It’s important for patients and their healthcare providers to know that some people have reported experiencing behavior or mood changes after discontinuing Singulair.

Withdrawal symptoms

Singulair is unlikely to t cause withdrawal symptoms. The manufacturer states that in their clinical studies there were no signs of rebound worsening asthma in adults after 12 weeks of continuous use of Singulair. It’s important for patients to discuss stopping Singulair with their healthcare provider before discontinuing it. 

How long do Singulair side effects last?

Some Singulair side effects will go away on their own over time. This includes headaches, an upset stomach, and indigestion. Some side effects may last longer than others or cause complications.

More severe side effects may require immediate medical attention including fever, difficulty breathing, difficulty swallowing, agitation, depression, mood changes, hives, and confusion.

A doctor should always be contacted if someone has severe side effects. A doctor will help control the symptoms and determine if the medication needs to be discontinued. Emergency services should be contacted if a person’s asthma gets worse or develops into severe shortness of breath with wheezing and a new cough (within the past three days). 

Singulair contraindications and warnings

Singulair may not be right for everyone and does carry a risk for all patients. A doctor will evaluate the benefits versus the risks before prescribing this medication.

People should not take Singulair if they are allergic to montelukast or any of the ingredients it contains. Some people may have difficulty taking the drug and should discuss possible alternative treatments with their doctors.


The standard adult dosing of Singulair is a 10 mg tablet by mouth once daily. It is possible to take too much of this medication, which could result in serious adverse reactions. According to the manufacturer, the majority of Singulair overdose cases do not result in severe adverse reactions. Symptoms of overdose include:

  • Abdominal pain and/or vomiting
  • Excessive drowsiness
  • Thirst
  • Headache
  • Agitation

People should call Poison Control or seek immediate emergency medical attention if they suspect an overdose.

Pregnancy and breastfeeding

Singulair may be used in pregnant women if their healthcare providers determine the use is necessary. For pregnant women with asthma, it is important that their asthmatic symptoms are well controlled throughout their pregnancy. This may mean that healthcare providers will continue a woman’s asthma therapy during her pregnancy, including Singulair. Research has not shown any signs of toxicity to unborn children of pregnant women taking Singulair.

Singulair is present in breast milk, so nursing mothers should discuss with their doctors if they should continue taking this medication while nursing. The manufacturer of Singulair advises caution when nursing, but for healthcare providers to discuss the benefits versus the risks with patients.

Restrictions and cautions

  •  Singulair is not meant to treat severe asthma exacerbations, like an asthma attack. People with asthma should have rescue inhalers available for severe asthma symptoms. 
  • Use extreme caution in patients with phenylketonuria (PKU), as the 4 mg and 5 mg chewable tablet forms are harmful to patients with this disorder. These chewable forms of Singulair contain phenylalanine.
  • Consider using an alternative medication in patients with a history of mental illness or psychosis, as Singulair has a black box warning. This warning is for serious neuropsychiatric events including agitation, aggression, depression, anxiety, disorientation, and hallucinations. Suicidal thoughts and behaviors have been reported while taking this medication. People should speak with their doctor immediately if they experience any behavior changes while taking Singulair.

Singulair interactions

Drug interactions are possible when taking Singulair. Some medications may alter the way this drug works, decreasing the serum levels within the body. Examples of medications that interact with Singulair include:

  • Barbiturates including pentobarbital, phenobarbital, butabarbital, and butalbital
  • Anticonvulsants including carbamazepine, fosphenytoin, phenytoin, and primidone
  • Androgen receptor inhibitors including apalutamide and enzalutamide
  • Cystic fibrosis medications including lumacaftor/ivacaftor
  • Antineoplastic agents including mitotane
  • Antimycobacterials including rifabutin and rifampin
  • St. John’s wort

How to avoid Singulair side effects

As with any medication, there are potential risks while taking Singulair. Although some side effects may not be prevented, it’s possible to minimize them by following the guidance of a doctor. Other ways to avoid side effects while taking Singulair include:

1. Tell the doctor about all medical conditions and medications

People with certain medical conditions are at higher risk of experiencing adverse effects while taking this medication. Be sure a healthcare provider is aware of any past or current medical conditions.

Singulair may interact with some medications, so it’s important for doctors to be aware of what medications are being taken before treatment. This includes any prescription drugs, over-the-counter medications, supplements, and herbal products.

2. Take Singulair as directed by the doctor

Follow the physician’s instructions when taking this medication. Read the entire label, along with the printed drug information given by the pharmacist. When used for asthma, Singulair is generally taken once daily by mouth before bed. When used for allergic rhinitis, Singulair is generally taken once daily by mouth in the morning or in the evening. For exercise-induced asthma, it may be taken in a single dose two hours before activity. It may take several weeks to see an improvement in symptoms. Always take the directed amount and avoid discontinuing without getting medical advice from a healthcare professional.

3. Be aware of changes in mood

Singulair has a black box warning for psychotic/mania symptoms, which can occur in people with depression. These symptoms may also occur in other people who take Singulair without having a history of psychiatric illness. Be aware of any changes in mood or behavior while taking this medication and report them to a doctor immediately if they’re severe or concerning. Be aware that some patients have reported these changes in behavior or mood after discontinuation of Singulair.

4. Don’t stop taking Singulair suddenly

Some side effects may be severe or intolerable. If this happens, discuss with a healthcare provider about ways to safely discontinue Singulair and options for alternative therapy.

5. Watch for signs of infection

Singulair can increase the chance of developing an upper respiratory infection, flu-like symptoms, sinus infection, or ear infection. Be aware of the symptoms of an upper respiratory infection such as a sore throat, stuffy nose, cough, painful swallowing, and sneezing. And watch for symptoms of ear infection such as ear pain, fever, hearing difficulties, and fluid drainage from the ears. If an infection is suspected, it’s best to contact a doctor for treatment.

6. Regular tablet must be swallowed whole

Drink an 8 oz glass of water when taking a Singulair tablet. Do not chew or crush. This can be taken with or without food. 

7. Chewable Singulair tablet must be chewed completely before swallowing

If taking the chewable form of this medication, be sure to chew the tablet fully before swallowing. This can be taken with or without food. People can rinse their mouth after taking the chewable tablets to rid any unpleasant flavor left behind.

8. Avoid stomach upset

Singulair may cause stomach upset including stomach pain, nausea, indigestion, or diarrhea. Singulair can be taken with or without food, so eating a snack with the dose of Singulair may help to settle the stomach and lessen upset. Additionally, the Singulair dose can be taken as close to bedtime as possible. This way people can rest in bed and fall asleep before any nausea develops.

9. Take Singulair at the same time every day

If a dose is missed, it’s important to continue with a regular schedule and take the next dose at the normal time. Never take two doses at once. It’s important to continue taking this medication every day even if a person is not actively having asthma or allergy symptoms

10. Keep Singulair at room temperature

In hot weather, do not keep Singulair in a car or any other place where it might get too hot. It’s important to avoid storing medications in bathrooms that have changes in temperature and humidity. Heat can cause the medication to lose its efficacy. Keep Singulair tablets in their original container, prescription vial, or pillbox. 

11. Avoid allergens

The best way to prevent allergy symptoms is to avoid the trigger altogether. Staying indoors on windy or high-pollen days, wearing a mask when exposed to triggers, and using air purifiers inside are some strategies for avoiding allergens.

12. Carry a rescue inhaler

Patients with asthma who use Singulair should always keep a rescue medication on hand. Singulair will not treat sudden asthma attacks. Examples of asthma rescue inhalers that contain the medication albuterol include Proair, Ventolin, and Proventil.