What the label lists and what reports show
Montelukast side effects
Montelukast's FDA label: “Most common adverse reactions (incidence ≥5% and greater than placebo listed in descending order of frequency): upper respiratory infection, fever, headache, pharyngitis, cough, abdominal pain, diarrhea, otitis media, influenza, rhinorrhea, sinusitis, otitis …” FAERS holds 174,997 reports naming it through July 30, 2026; the reaction reported most often, leaving out the conditions it is used for, product-use terms and outcomes, is dyspnoea (19,390 reports).
- Generic listed
- A presentation discontinued
- Boxed warning
Check it at the source: the montelukast FDA label on DailyMed (effective April 30, 2025, Organon LLC); the FDA FAERS public dashboard.
What does the patient leaflet say about side effects?
From the patient leaflet: What are the possible side effects of SINGULAIR?SINGULAIR may cause serious side effects, including: See “What is the most important information I should know about SINGULAIR?” Increase in certain white blood cells (eosinophils) and possible inflamed blood vessels throughout the body (systemic vasculitis). Rarely, this can happen in people with asthma who take SINGULAIR. This sometimes happens in people who also take a steroid medicine by mouth that is being stopped or the dose is being lowered. […]
Source: FDA drug label, Organon LLC, effective April 30, 2025 (SPL set 482dcc92-b47f-4ea6-854a-f5ac2aea7842), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsMost common adverse reactions (incidence ≥5% and greater than placebo listed in descending order of frequency): upper respiratory infection, fever, headache, pharyngitis, cough, abdominal pain, diarrhea, otitis media, influenza, rhinorrhea, sinusitis, otitis ( 6.1 ).
Table 5: Adverse Reactions Occurring in ≥1% of Patients with an Incidence Greater than that in Patients Treated with Placebo
This table is printed in the Montelukast Sodium label published by Torrent Pharmaceuticals Limited of July 28, 2026; the label quoted above does not print one.
| Reaction | Montelukast 10 mg/day (%) (n=1,955) | Placebo (%) (n=1,180) |
|---|---|---|
| Pain, abdominal | 2.9 | 2.5 |
| Asthenia/fatigue | 1.8 | 1.2 |
| Fever | 1.5 | 0.9 |
| Trauma | 1.0 | 0.8 |
| Dyspepsia | 2.1 | 1.1 |
| Pain, dental | 1.7 | 1.0 |
| Gastroenteritis, infectious | 1.5 | 0.5 |
| Headache | 18.4 | 18.1 |
| Dizziness | 1.9 | 1.4 |
| Influenza | 4.2 | 3.9 |
| Cough | 2.7 | 2.4 |
| Congestion, nasal | 1.6 | 1.3 |
| Rash | 1.6 | 1.2 |
| ALT increased | 2.1 | 2.0 |
| AST increased | 1.6 | 1.2 |
| Pyuria | 1.0 | 0.9 |
Rows and numbers as the label prints them, under its own column headings (the first rows of a longer table where it runs on). A reaction in a trial table is not necessarily caused by the medicine, and trials differ from everyday use.
From the label: adverse reactions, continuedThe following clinically significant adverse reactions are described elsewhere in the labeling: Neuropsychiatric Events [see Warnings and Precautions (5.1) ] Most common adverse reactions (incidence ≥5% and greater than placebo listed in descending order of frequency): upper respiratory infection, fever, headache, pharyngitis, cough, abdominal pain, diarrhea, otitis media, influenza, rhinorrhea, sinusitis, otitis ( 6.1 ). To report SUSPECTED ADVERSE REACTIONS, contact Organon LLC, a subsidiary of Organon & Co., Inc., at 1-844-674-3200 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. 6.1 Clinical Trials Experience Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in clinical practice. In the following description of clinical trials experience, adverse reactions are listed regardless of causality assessment. The most common adverse reactions (incidence ≥5% and greater than placebo; listed in descending order of frequency) in controlled clinical trials were: upper respiratory infection, fever, headache, pharyngitis, cough, abdominal pain, diarrhea, otitis media, influenza, rhinorrhea, sinusitis, otitis. …
Source: FDA drug label, Organon LLC, effective April 30, 2025 (SPL set 482dcc92-b47f-4ea6-854a-f5ac2aea7842), via openFDA; the full label on DailyMed
What do FAERS reports show?
174,997 reports list montelukast among the medicines taken, each a report of something that happened, not proof the medicine caused it; 7,487 are coded as a death and 47,569 as a hospital stay. Counts follow how widely a medicine is used and watched, and they are not a measure of how risky it is. Of the 22 reactions below, 15 are named by the same term (in US spelling) in the label's adverse reactions, warnings or patient leaflet; a reaction the label does not name may still be there under another word, and a report does not show that the medicine caused it.
Reports received each year
The 25 most reported reactions
Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms
What next?
- Montelukast: the full record
- label, generics, price, shortages, recalls
- Report a side effect to the FDA
- MedWatch
- Side effects hub
- the most reported medicines and reactions