Montelukast (Singulair) Side Effects: Mental Health Warnings and More

In March 2020, the FDA took the unusual step of adding a boxed warning — often called a “black box” warning, the most serious type of drug warning — to montelukast (Singulair) for neuropsychiatric side effects including suicidal thoughts, aggression, and depression. This decision fundamentally changed how doctors prescribe this widely used asthma and allergy medication. Understanding montelukast side effects is now more important than ever, as the drug remains useful for the right patients but carries risks that were previously underappreciated. Montelukast is dispensed only with a prescription, and both patients and caregivers need to know what to watch for. Explore more medication information in our medical conditions guide.

The FDA Boxed Warning Explained

The FDA’s boxed warning, announced on March 4, 2020, was prompted by decades of post-marketing reports linking montelukast to serious mental health and behavioral changes. The warning notes that montelukast can cause agitation (including aggressive behavior or hostility), attention problems, vivid or abnormal dreams, depression, disorientation or confusion, anxiousness, hallucinations, irritability, memory problems, obsessive-compulsive symptoms, restlessness, sleepwalking, stuttering, tremor, insomnia, and suicidal thoughts and actions (including suicide).

The FDA specifically advises that, for allergic rhinitis (hay fever), montelukast “should be reserved for those who are not treated effectively with or cannot tolerate other allergy medicines,” because safer over-the-counter antihistamines and nasal sprays are available. For asthma, the benefits may outweigh the risks for some patients, but the decision requires a careful risk-benefit discussion with a prescriber. The warning is relevant across age groups, including young children for whom the medication is approved.

These neuropsychiatric events have occurred during treatment and after discontinuation. Some reports describe symptoms appearing within days of starting montelukast, while others emerged after months or years of use. The unpredictable timing is exactly why the FDA urges patients and caregivers to stay alert throughout treatment and to talk with a health care professional right away if behavior or mood changes appear.

Common Montelukast Side Effects

Setting aside the neuropsychiatric concerns, montelukast has a relatively mild common side-effect profile for most people. Reported montelukast side effects that are generally milder include:

Headache is among the most commonly reported side effects. Upper respiratory infection symptoms such as cough, nasal congestion, and sore throat are also reported. Abdominal (stomach) pain, heartburn, tiredness, and diarrhea occur in some users. Influenza-like symptoms including fatigue and general malaise have also been noted. According to MedlinePlus, many of these milder effects do not require stopping the medicine, but you should tell your prescriber if they are severe or do not go away.

In children, the most common side effects mirror those in adults, with diarrhea, ear infections (otitis media), pharyngitis, and nausea additionally noted according to the Mayo Clinic. Exact frequencies vary between sources, so treat any percentage figures you see online as approximate and verify current details with your pharmacist or the FDA-approved labeling.

Mental Health Side Effects in Detail

The mental health side effects of montelukast deserve detailed attention because they can be subtle at first and are sometimes attributed to other causes before the medication connection is recognized.

Sleep disturbances and vivid dreams are among the earliest reported neuropsychiatric effects. Parents frequently report that children on montelukast experience nightmares, night terrors, or difficulty falling asleep. In adults, vivid or disturbing dreams and insomnia are common complaints. Sleepwalking has also been documented.

Behavioral changes in children can include increased aggression, irritability, hyperactivity, and attention difficulties. Some parents and teachers notice personality changes that may initially be attributed to developmental stages or other factors, which can delay recognizing the medication as a possible cause.

Depression and anxiety in adults may develop gradually. Patients report feeling increasingly anxious, hopeless, or emotionally flat while taking montelukast. Because depression and anxiety are common conditions, the connection to montelukast is not always immediately apparent, especially if the medication was started months earlier.

Suicidal thoughts and behavior are the most serious reported effects. While rare in absolute terms, the FDA determined these reports were significant enough to warrant the highest level of warning. Any emergence of suicidal thinking in a person taking montelukast should prompt immediate medical evaluation. If there is any immediate danger, call 911 or go to the nearest emergency department; for thoughts of suicide or a mental-health crisis, call or text 988.

Who Is at Higher Risk?

Research has not definitively identified which patients are most susceptible to neuropsychiatric montelukast side effects, but certain patterns have emerged. Children appear to experience behavioral side effects at notable rates. Patients with a pre-existing history of depression, anxiety, or other mental health conditions may be more vulnerable. Some case reports suggest a possible genetic component related to leukotriene metabolism, but this is not established well enough to guide clinical testing.

Given this uncertainty, many clinicians advise particular caution in patients with a personal or family history of mental health disorders and recommend discussing these risk factors with your prescriber before starting montelukast. This is a decision to make with your clinician, not on your own.

Allergic and Immune-Related Side Effects

Rarely, montelukast has been associated with eosinophilic conditions, including eosinophilic granulomatosis with polyangiitis (formerly Churg-Strauss syndrome), a serious form of vasculitis. This has primarily been reported in patients whose oral corticosteroids were reduced as montelukast was added, raising questions about whether montelukast unmasked a pre-existing condition. Symptoms to watch for include worsening breathing, numbness or tingling in the limbs, rash, and flu-like symptoms that do not resolve; report these to your clinician promptly.

Allergic reactions to montelukast itself, including angioedema and anaphylaxis, are very rare but have been reported. More commonly, patients may experience a mild rash or hives. A severe allergic reaction — trouble breathing, swelling of the face, lips, tongue, or throat — is a medical emergency; call 911.

What to Do If You Experience Side Effects

If you or your child experience any mental health or behavioral changes while taking montelukast, contact your healthcare provider promptly — do not wait for your next scheduled appointment. The FDA advises stopping montelukast and discussing it with a health care professional right away if behavior or mood-related changes occur. Any change to your treatment — stopping, switching, or adjusting — should be directed by your prescriber, because untreated asthma can itself be dangerous. Do not restart the medicine on your own afterward.

Keep in mind that some neuropsychiatric symptoms have persisted after montelukast was stopped, though many resolve within days to weeks of discontinuation. Document the timeline of symptom onset relative to when you started or changed your montelukast, as this information helps your doctor assess causality. Reporting side effects also helps others: you or your clinician can report them to the FDA’s MedWatch program.

For context on how montelukast compares to alternative allergy treatments, see our montelukast vs cetirizine comparison. Any decision to switch medicines should be made with your clinician.

Frequently Asked Questions

Should I stop taking montelukast because of the boxed warning?

Do not stop any prescription medication without talking to your doctor. The boxed warning does not mean montelukast is unsafe for everyone; it means the decision to use it should involve a careful discussion of risks and benefits. For patients with asthma who have not responded well to other treatments, montelukast may still be the best option. For allergic rhinitis alone, alternatives like antihistamines and nasal corticosteroids should generally be tried first. If you have concerns, call your prescriber.

How quickly do montelukast mental health side effects appear?

There is no consistent timeline. Some patients report behavioral changes within the first few days, while others develop symptoms after weeks, months, or even years of use. This variability makes ongoing monitoring important throughout the entire treatment period, not just at the start.

Is montelukast safe for children?

Montelukast is FDA-approved for certain young children for asthma and allergic rhinitis, but the FDA’s updated guidance recommends that for hay fever it be reserved for children who cannot tolerate or are not helped by other treatments. Parents and caregivers should monitor closely for behavioral changes, sleep disturbances, and mood shifts, and discuss the risks and benefits with the child’s clinician. Follow only the dose the prescriber orders.

Does montelukast cause weight gain?

Weight gain is not listed as a common side effect of montelukast. Some patients report appetite changes, but clinical trial data do not show a significant association between montelukast and weight change. Discuss any unexplained weight changes with your clinician.

Can montelukast be taken with antihistamines?

Montelukast and antihistamines such as cetirizine or loratadine work through different mechanisms, and clinicians sometimes use them together for allergies not controlled by either alone. Even so, confirm any combination with your prescriber or pharmacist, and always review your full medication list with them for interactions.

The Bottom Line

Montelukast remains a valuable medication for specific patients, particularly those with asthma combined with allergies or exercise-induced bronchoconstriction who have not responded to first-line treatments. The FDA’s boxed warning does not make it a uniformly “dangerous” drug, but it does make it one that requires informed consent, appropriate patient selection, and vigilant monitoring for mood and behavior changes. If you are currently taking montelukast without issues, do not stop on your own — talk with your prescriber if you have questions. If you are considering starting it, have an honest conversation with your doctor about your mental health history, explore whether alternatives might work first, and know what behavioral and mood changes to watch for. Drug information can change, so verify current details with your pharmacist, the FDA-approved labeling, or MedlinePlus.

Sources

• U.S. Food and Drug Administration — FDA Drug Safety Communication: boxed warning for montelukast (March 4, 2020)
• MedlinePlus (U.S. National Library of Medicine) — Montelukast
• Mayo Clinic — Montelukast (oral route) side effects
• 988 Suicide & Crisis Lifeline — 988lifeline.org; Poison Control — poison.org (1-800-222-1222)