Montelukast (Singulair) is a generic prescription medication used to:

  • help prevent exercise-induced bronchoconstriction (formerly called exercise-induced asthma) in adults and children ages 6 years and older
  • treat asthma in adults and children ages 15 years and older
  • treat symptoms of allergic rhinitis in adults and children ages 15 years and older who either can’t use other treatments, or who didn’t get enough relief from other treatments

Montelukast is typically a long-term treatment. You will likely take it long term if you and your doctor agree that it’s safe and working well to treat your condition.

Montelukast comes as an oral tablet. It also comes in chewable tablets and granules, but this article does not cover them.

As with other drugs, montelukast can cause side effects. Read on to learn about potential common, mild, and serious side effects.

For a general overview of montelukast, including details about its uses, refer to this article. Your doctor can also tell you more about montelukast.

Montelukast can cause certain side effects, some of which are more common than others. These side effects may be temporary, lasting a few days to weeks. However, if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

These are just a few of the more common side effects reported by people who took montelukast in clinical trials:

Mild side effects can occur with montelukast use. This list doesn’t include all possible mild side effects of the drug. For more information, you can refer to montelukast’s prescribing information.

Mild side effects that have been reported with montelukast include:

These side effects may be temporary, lasting a few days to weeks. However, if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks side effects of the medication. If you develop a side effect while taking Montelukast and want to tell the FDA about it, visit MedWatch.

* For more information about this side effect, see “Montelukast: Side effect specifics” below.

Montelukast may cause serious side effects, although they’re rare. The list below may not include all possible serious side effects of the drug. For more information, you can refer to montelukast’s prescribing information.

If you develop serious side effects while taking montelukast, call your doctor right away. If the side effects seem life threatening or you think you’re having a medical emergency, immediately call 911 or your local emergency number.

Serious side effects that have been reported (and are discussed in more detail below) include:

* For more information about this side effect, see “Montelukast: Side effect specifics” below.
† Montelukast has a boxed warning for this side effect. This is a serious warning from the Food and Drug Administration (FDA). To learn more, see the “Montelukast: Side effect specifics” section below.
‡ An allergic reaction is possible after using montelukast. However, it’s not clear whether this side effect occurred in clinical trials. To learn more, see the “Montelukast: Side effect specifics” section below.

Montelukast may cause several side effects. Here are some frequently asked questions about the drug’s side effects and their answers.

Does montelukast 10 mg cause different side effects in adults vs. children?

No, it’s not expected to. In clinical trials, different side effects weren’t reported in adults versus children taking the 10-milligram (mg) tablet.

To learn more about side effects montelukast can cause, talk with your pharmacist or doctor. Your child’s pediatrician can explain possible side effects of the drug in children.

Is weight gain or weight loss a side effect of montelukast?

No, weight gain and weight loss are not expected side effects of montelukast. These weight changes weren’t reported side effects in the drug’s clinical trials.

Some treatments for asthma may cause weight gain. Specifically, oral steroids, such as Rayos (prednisone), can cause this side effect. However, montelukast is not a steroid.

If montelukast works well to treat your asthma symptoms, it may become easier to exercise. This could lead to weight loss. However, in most cases, this weight loss shouldn’t be severe. If you experience unexplained weight loss, contact your doctor. They can help determine what may be causing your weight loss.

Talk with your doctor if you have concerns about weight management. They can recommend ways to maintain a weight that’s healthy for you.

Can montelukast cause hair loss?

No, it’s not expected to. Hair loss wasn’t reported as a side effect in montelukast’s clinical trials.

However, some studies suggest a possible link between hair loss and certain conditions montelukast is prescribed to treat. Specifically, people with allergic rhinitis or asthma may be more likely to experience hair loss than people without either condition. However, more research is necessary to know for sure whether either condition can cause hair loss.

If you have any concerns about hair loss and montelukast, talk with your doctor. They can help determine what may be causing your hair loss.

Learn more about some of the side effects that montelukast may cause, including a boxed warning about the risk of serious behavior or mood changes. To find out how often side effects occurred in clinical trials, see the prescribing information for montelukast.

Risk of serious behavior or mood changes

Montelukast has a boxed warning for the risk of serious behavior or mood changes. This is a serious warning from the Food and Drug Administration (FDA). It alerts doctors and patients about drug effects that may be dangerous.

Psychiatric and mental health side effects have been reported with montelukast since the drug was approved for use. Because these reports happened outside of clinical trials, it’s not clear exactly how often they occur. However, they’re believed to be rare.

Mental health and psychiatric side effects reported since the montelukast was approved include:

In most cases, these reactions happened during treatment with montelukast. However, it’s possible for symptoms to appear for the first time after you stop treatment.

What you can do

Before you start taking montelukast, tell your doctor about your treatment goals and medical history. They can discuss the possible risks and benefits of this treatment option with you.

Certain mental health conditions can increase your risk of the above side effects during treatment. Due to this risk, doctors typically will not prescribe montelukast if you have a history of severe mental health conditions.

If your doctor prescribes montelukast, they’ll closely monitor for changes in your behavior or mood during treatment. It may also be helpful to tell close friends or family that you’re taking montelukast. This way, they can help monitor for any changes in your behavior or mood.

Immediately tell your doctor if you notice any of the above symptoms while taking montelukast. These side effects typically go away shortly after stopping treatment, though they can last for longer periods. However, long-term mental and psychiatric side effects are rare.

Your doctor will likely monitor your symptoms closely after stopping treatment until you no longer experience symptoms related to your mood and behavior.

Cough

It’s possible to experience a cough as a side effect while taking montelukast. It’s one of the most common side effects reported in the drug’s clinical trials.

A cough can also be a symptom of conditions montelukast is prescribed to treat, including asthma. If your cough is a symptom of your condition, it may ease as you continue taking the drug.

What you can do

If you develop a mild cough while taking montelukast, a home remedy or over-the-counter (OTC) treatment may be effective in treating your symptoms. Some examples include:

There are several possible causes for a cough. While taking montelukast, let your doctor know if you develop a cough that bothers you or won’t go away. Your doctor will likely want to check for other possible causes. If montelukast is causing your cough and it doesn’t go away with treatment, your doctor will likely recommend that you stop taking the medication.

Liver problems

Liver problems have been reported in clinical trials and since montelukast was approved for use.

In clinical trials, the only liver problem reported was mildly elevated liver enzyme levels. A severe increase in liver enzyme levels can be a sign of liver damage. However, liver damage wasn’t reported in montelukast’s clinical trials.

More serious liver problems, including liver injury, have been reported since the drug was approved for use. However, most serious liver side effects occurred in people with preexisting risk factors for liver problems. For example, these risk factors included hepatitis and heavy alcohol consumption.

Symptoms of liver problems can include:

What you can do

Your doctor may check your liver health before prescribing montelukast. This may include a blood test to check your liver enzyme levels.

If you notice the above symptoms while taking montelukast, contact your doctor right away.

Increased eosinophil level

Treatment with montelukast can cause an increased level of eosinophils, which is a type of white blood cell. However, this wasn’t common in the drug’s clinical trials. In most cases, a mildly increased eosinophil count won’t cause symptoms.

Rarely, an increased eosinophil level can lead to severe vasculitis (swelling throughout your blood vessels). Severe vasculitis is also called Churg-Strauss syndrome. Symptoms can include:

People taking montelukast to treat asthma may have a higher risk of this side effect. Your risk may also be higher if you’re currently taking a steroid and stop or reduce your dosage. (Prednisone is an example of a steroid medication.) This risk is the same for all conditions montelukast is prescribed to treat.

What you can do

Let your doctor know if you have any symptoms of vasculitis described above while taking montelukast. They’ll likely have you stop taking montelukast and recommend treatment options for your vasculitis.

Allergic reaction

As with most drugs, montelukast can cause an allergic reaction in some people. However, this side effect wasn’t common in clinical trials.

Symptoms can be mild or serious and can include:

  • skin rash
  • itching
  • flushing
  • swelling under your skin, typically in your eyelids, lips, hands, or feet
  • swelling of your mouth, tongue, or throat, which can make it hard to breathe

Life threatening allergic skin reactions, including Stevens-Johnson syndrome, have been reported with montelukast since the drug was approved. Symptoms can include:

  • discolored skin patches that blister and peel in various areas, such as the eyes, genitals, mouth, and throat
  • raw, painful areas of skin
  • body aches
  • fever
  • general sense of feeling unwell
  • flu-like symptoms, such as a cough

What you can do

For mild symptoms of an allergic reaction, call your doctor right away. They may recommend ways to ease your symptoms and determine whether you should keep taking Montelukast. However, if your symptoms are serious and you think you’re having a medical emergency, immediately call 911 or your local emergency number.

Suicide prevention

If you know someone at immediate risk of self-harm, suicide, or hurting another person:

  • Ask the tough question: “Are you considering suicide?”
  • Listen to the person without judgment.
  • Call 911 or the local emergency number, or text TALK to 741741 to communicate with a trained crisis counselor.
  • Stay with the person until professional help arrives.
  • Try to remove any weapons, medications, or other potentially harmful objects.

If you or someone you know is having thoughts of suicide, a prevention hotline can help. The 988 Suicide and Crisis Lifeline is available 24 hours a day at 988. During a crisis, people who are hard of hearing can use their preferred relay service or dial 711 then 988.

Click here for more links and local resources.

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There are certain precautions to consider before taking montelukast. This includes a boxed warning about the risk of serious behavior or mood changes while taking the drug.

Boxed warning: Risk of serious behavior or mood changes

This drug has a boxed warning for the risk of serious behavior or mood changes. This is a serious warning from the Food and Drug Administration (FDA). For details, see the “Montelukast: Side effect specifics” section above.

Other precautions

Be sure to talk with your doctor about your health history before you take montelukast. This drug may not be the right treatment for you if you have certain medical conditions or other factors that affect your health. These are considered drug-condition or drug-factor interactions. The conditions and factors to consider include:

Sensitivity to aspirin. Aspirin and certain nonsteroidal anti-inflammatory drugs (NSAIDs) can trigger asthma symptoms in some people. This is known as aspirin sensitivity. Before you start taking montelukast, tell your doctor if you have aspirin sensitivity.

Taking montelukast does not make it safe for you to take aspirin or NSAIDS, such as ibuprofen (Advil, Motrin). Your doctor will likely recommend that you still do not take these medications.

Liver problems. Since montelukast was approved for use, there have been rare reports of liver problems. Some conditions, such as hepatitis, can be serious. In most cases, people who developed liver problems while taking montelukast had other risk factors. These risk factors included preexisting liver conditions, such as hepatitis.

If you have a liver problem, be sure to let your doctor know before you start taking montelukast. They can determine whether the drug is safe for you to take.

Allergic reaction. If you’ve had an allergic reaction to montelukast or any of its ingredients, your doctor will likely not prescribe montelukast. Taking montelukast could cause you to have another allergic reaction. Ask your doctor what other medications may be better options for you.

Alcohol with montelukast

If you drink alcohol, your doctor may advise limiting your intake while taking montelukast. While there are no specific interactions between montelukast and alcohol, both can cause liver problems.

Since montelukast was approved for use, there have been rare reports of liver problems. Some conditions, such as hepatitis, can be serious. In most cases, people who developed liver problems while taking montelukast had other risk factors, including heavy alcohol consumption. This is because both alcohol and montelukast are broken down by the liver.

Additionally, certain substances in alcohol, such as sulfites, may contribute to asthma attacks in some people.

Talk with your doctor to discuss how much alcohol, if any, is safe for you to drink while taking montelukast.

Pregnancy and breastfeeding while taking montelukast

Montelukast may be safe to take during pregnancy. In clinical trials of the drug during pregnancy, there was no reported risk of fetal harm. Additionally, unmanaged asthma, which montelukast is prescribed to treat, may increase the risk of certain pregnancy complications. These complications may include preeclampsia, preterm labor, and low birth weight.

Montelukast does pass into breast milk. However, according to clinical trials, it doesn’t cause side effects in children who are breastfed.

Talk with your doctor if you have additional questions about taking montelukast during pregnancy or while breastfeeding. They can help you weigh the risks and benefits for your specific condition.

As with most medications, montelukast can cause side effects. Most side effects are mild and go away on their own as you continue taking the medication.

Serious side effects are possible, though they are rare. The drug does have a boxed warning due to the risk of serious behavior or mood changes. A boxed warning is a serious warning from the Food and Drug Administration (FDA). It alerts doctors and patients about serious side effects a drug may cause.

If you’d like to learn more about montelukast, talk with your doctor or pharmacist. They can help answer any questions you have about side effects from taking the drug. You can also ask them about Singulair, the brand-name version of montelukast.

A generic drug and its brand-name version contain the same active ingredient, so they’re expected to have the same side effects.

Referring to the following articles about montelukast can provide you with additional information:

  • More information about montelukast. For details about other aspects of montelukast refer to this article.
  • A look at asthma and allergic rhinitis. For details about asthma and allergic rhinitis, see our asthma and allergies hub.

Disclaimer: Medical News Today has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.