Singulair (montelukast) occupies an unusual spot in medicine cabinets: a once-daily tablet prescribed for both asthma and allergies, taken by millions including many children, that also carries the FDA's strongest safety warning. Both facts are true at once, and understanding them calmly is more useful than either ignoring the warning or panicking over it.
What Singulair is and how it works
Montelukast is a leukotriene receptor antagonist. While antihistamines block histamine, montelukast blocks leukotrienes, a different set of inflammatory messengers involved in airway tightening and allergic inflammation. That's why it's prescribed across asthma, exercise-induced breathing symptoms, and allergic rhinitis, often as a pill-based add-on when inhalers or antihistamines aren't enough on their own.
The common side effects
For most people, day-to-day side effects are mild and unremarkable:
- Headache, the most commonly reported
- Stomach upset or abdominal pain
- Cold-like upper respiratory symptoms
- Fatigue in some patients
The boxed warning, explained without panic
In March 2020, the FDA added a boxed warning, its most serious category, to montelukast for neuropsychiatric events reported in some patients: agitation, vivid dreams and sleep disturbance, anxiety, irritability, depression, and in rare cases suicidal thoughts and actions. Reports span adults and children, and in kids the changes often surfaced as behavior shifts that parents noticed before anyone connected them to the medication.
Two balanced truths: most people who take montelukast never experience these effects, and the association is serious enough that the FDA also advised reserving montelukast for allergic rhinitis only when other treatments haven't worked. The practical takeaway isn't fear, it's vigilance: know the signal, watch for it, and act early.
What to watch for, especially in kids
- New irritability, aggression, or agitation without another explanation
- Nightmares, vivid dreams, or new sleep problems
- Anxiety, low mood, or withdrawal from usual activities
- Any talk of self-harm, which warrants immediate medical contact
If you notice these, contact the prescriber promptly rather than stopping on your own. A supervised change protects the asthma or allergy control the medication was providing while the switch happens.
The families who handle montelukast well are the ones who know exactly what to watch for. The warning is not a reason to refuse a useful medicine. It is a reason to stay observant.Kayla Mardaga, NP-C, Allergy & Asthma
The bigger question: why is the allergy there at all?
Montelukast for allergic rhinitis is a pathway blocker: useful, but it manages output from an immune system that has misclassified pollen, dust, or dander as threats. The FDA's own guidance nudges toward trying other options first for allergies, and the option that actually addresses the misclassification is allergen immunotherapy. For allergic asthma specifically, treating the allergic root can reduce the trigger load on the airways, as we covered in the allergy-asthma link. And sublingual immunotherapy does it at home, without adding another daily pathway-blocker to the cabinet.
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Join Thousands Finding ReliefFrequently Asked Questions
What are the most common Singulair side effects?
The everyday side effects of montelukast are usually mild: headache, stomach upset, and upper respiratory symptoms are the most reported. The reason Singulair gets extra attention is a separate category: mood and behavior changes, which led the FDA to add a boxed warning in 2020.
What is the FDA boxed warning on Singulair?
In March 2020 the FDA added its most serious warning to montelukast for neuropsychiatric events reported in some patients, including agitation, vivid dreams, sleep disturbance, anxiety, depression, and in rare cases suicidal thoughts. The FDA also advised that for allergic rhinitis, montelukast should generally be reserved for people who have not responded adequately to other therapies.
Should I stop taking Singulair?
Not on your own. If you or your child notice mood, sleep, or behavior changes on montelukast, contact your prescriber promptly to discuss it. There are alternative strategies for both asthma and allergies, and the right move is a supervised change, not an abrupt stop.
What are alternatives to Singulair for allergies?
For allergic rhinitis, options include nasal steroid sprays, antihistamines, and allergen immunotherapy, which treats the underlying allergic response rather than blocking one inflammatory pathway. For asthma, inhaled controller options exist. The right alternative depends on why montelukast was prescribed, which is a prescriber conversation.