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Singulair, also known as montelukast, is a prescription medication used to prevent symptoms of asthma, such as difficulty breathing, chest tightness, wheezing and coughing. It’s also used to prevent asthma symptoms during exercise and to relieve hay fever (allergies).

Last Modified: September 5, 2023
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Merck Sharp & Dohme Corp., a subsidiary of Merck & Co. Inc., markets Singulair in the United States. The U.S. Food and Drug Administration originally approved the drug in 1998. It’s sold under its brand name and in generic form.

“While Singulair is not a steroid and is not typically considered an immunosuppressant, it nevertheless does interfere with immune pathways by limiting the production of leukotrienes, chemicals in the body that are part of the ‘inflammatory cascade,’” Dr. Caleb Alexander, a professor at Johns Hopkins Bloomberg School of Public Health and co-director of the Center for Drug Safety and Effectiveness, told Drugwatch.

The body releases leukotrienes after coming in contact with an allergen. The chemicals cause tightening of the airway muscles and produce fluid and mucus. Singulair blocks these chemicals to help control asthma and allergy symptoms.

Singulair isn’t for sudden asthma attacks. Patients should follow instructions from their health care provider for treating asthma attacks, such as using an inhaler.

How to Take Singulair

Singulair is available in 10 mg tablets, 5 mg and 4 mg chewable tablets and 4 mg oral granules. This medicine can be used in people 12 months or older for asthma, and the dosage varies by age.

The FDA also approved it to treat exercise-induced asthma in people 6 years and older and allergic rhinitis in people 2 years and older, also called hay fever.

People can take this medication with or without food. If you miss a dose, don’t take two doses at the same time — wait until your next scheduled dose.


The recommended dose varies by age from 4 mg to 10 mg depending on age and may include tablets, chewable tablets and granules.

The drug’s label recommends taking the drug at night because the drug wasn’t tested in the morning during clinical trials, but the medication guide instructs people to take their medicine as prescribed by their medical providers.

“Sometimes we dose Singulair at night because many people have worse asthma symptoms at night than during the day,” Alexander said. “However, many people take Singulair during the morning rather than evening, and what works for one person may not work for another. In other words, there is no one-size-fits-all approach, and it’s more important to take it regularly than it is to take it at a certain hour of the day.”

Preventing Exercise-Induced Bronchoconstriction

In addition to treating asthma, Singulair can help people with breathing problems brought on by exercise. People should take the drug at least two hours before exercise, according to the drug’s label.

People 15 years of age and older take one 10 mg tablet. Children six to 14 years of age take one 5 mg chewable tablet.

Don’t take another dose within 24 hours of the previous dose. If you are already taking Singulair for asthma, don’t take an additional dose before exercise.

Allergic Rhinitis (Hay Fever)

People treating allergies should take Singulair once daily in the morning or evening. In clinical trials, the drug worked just as well regardless of the time of day or if taken with or without food.

The drug can also be taken as needed for perennial allergies as recommended by a medical provider.

Recommended doses:
  • Adults and adolescents 15 years of age and older, one 10-mg tablet
  • Children six to 14 years of age, one 5-mg chewable tablet
  • Children two to five years of age, one 4-mg chewable tablet or one packet of 4-mg oral granules

Side Effects

Most side effects associated with Singulair are mild. In general, the medication is well tolerated in people taking it for asthma or allergies, according to Alexander.

“Of course, all medicines have risks, and most medicines have rare but serious risks. In the case of Singulair, the most common adverse effects include upper respiratory infections, fevers, headaches and sore throat,” he said. “Of course, it is often difficult to know for sure whether these types of symptoms represent an adverse drug reaction or some other process.”

Singulair was tested in 2,950 adult and adolescent patients, and 1,955 people received the drug. In 2022 clinical trials, the most common side effects occurred in 5% or more of people who took Singulair.

Side effects with an incidence of 5% or more and greater than placebo in clinical trials include:
  • Upper respiratory infection
  • Fever
  • Headache
  • Pharyngitis (sore throat)
  • Cough
  • Abdominal pain
  • Diarrhea
  • Otitis media (ear inflammation or infection)
  • Influenza (flu)
  • Rhinorrhea (runny nose)
  • Sinusitis (sinus infection)

Other minor, less common side effects include body pain, fatigue, fever, indigestion, dizziness, rash and abnormal liver enzymes.

If you experience side effects, please inform your medical provider.

Drug Interactions

Singulair may interact with other substances. Make sure to tell your medical provider about all medications, supplements, herbs or vitamins you are taking.

The prescription information doesn’t list any specific drug interactions, but it recommends that people with aspirin sensitivity avoid aspirin or other nonsteroidal anti-inflammatory drugs while taking Singulair.

People who were diagnosed with a mental health disorder after taking Singulair are filing lawsuits against the drug's manufacturer.
View Lawsuits

Black Box Warning for Serious Neuropsychiatric Events

In March 2020, the FDA required Merck to place a black box warning — the agency’s most prominent warning — on Singulair drug labels warning about the risk of serious mental health problems, also called neuropsychiatric events. These include: agitation, aggression, depression, sleep disturbances, suicidal thoughts and behavior (including suicide).

“We recognize that millions of Americans suffer from asthma or allergies and rely on medication to treat these conditions. The incidence of neuropsychiatric events associated with montelukast is unknown, but some reports are serious, and many patients and health care professionals are not fully aware of these risks,” Dr. Sally Seymour, director of the Division of Pulmonary, Allergy and Rheumatology Products in the FDA’s Center for Drug Evaluation and Research, said in a statement.

The benefits of Singulair might not outweigh the risks in some people with allergic rhinitis. The FDA recommends the drug only be used in people who don’t respond to or cannot use other allergy treatments. Talk about the risks and benefits of this medication with your medical provider.

Mental health symptoms may occur in people with or without a history of mental health issues, according to the drug’s medication guide. Notify your medical provider right away if you experience changes in thoughts or behavior. Discuss Singulair alternatives that might be the right option for you.

Unusual thinking or behavior may include:
  • Agitation, including aggressive behavior or hostility
  • Attention problems
  • Bad or vivid dreams
  • Depression
  • Disorientation (confusion)
  • Feeling anxious
  • Hallucinations (seeing or hearing things that are not really there)
  • Irritability
  • Memory problems
  • Obsessive-compulsive symptoms
  • Restlessness
  • Sleep walking
  • Stuttering
  • Suicidal thoughts and actions (including suicide)
  • Tremor
  • Trouble sleeping
  • Uncontrolled muscle movements

Litigation over Side Effects

After the FDA placed the black box warning on the drug, some people filed Singulair lawsuits against Merck claiming the drugmaker failed to warn about the risk of suicidal thoughts and other neuropsychiatric problems.

One plaintiff from Wisconsin filed a lawsuit on behalf or her child in September 2020. According to her complaint, Merck ignored studies that showed Singulair could cause neuropsychiatric events.

After taking Singulair, her child was admitted to a psychiatric center and was diagnosed with “major depressive disorder, anxiety disorder, obsessive-compulsive disorder, ego-dystonic and intrusive thoughts about homicidal, suicidal, and sexual thoughts, and poor coping.”

“Originally, the Singulair label contained no warnings regarding neuropsychiatric events. Over the past 22 years Defendant has slowly and belatedly added grossly insufficient warnings regarding neuropsychiatric events to the product label,” her lawsuit claimed.

Merck hasn’t issued a statement about the lawsuits.

Please seek the advice of a medical professional before making health care decisions.