Montelukast Side Effects
Montelukast has minimal side effects in most patients, but carries a significant FDA black box warning for serious neuropsychiatric adverse events including suicidal thoughts, depression, anxiety, sleep disturbances, and behavioral changes—particularly in younger patients.
Primary Safety Concerns
Neuropsychiatric Effects (FDA Black Box Warning)
The most critical safety issue with montelukast is neuropsychiatric adverse events. In 2020, the FDA issued a black box warning about serious behavior and mood-related changes, including suicidal thoughts or actions 1. This warning fundamentally changed the risk-benefit assessment for montelukast use.
Recent large-scale evidence presents conflicting findings:
- A 2025 Swedish nationwide cohort study of 74,291 children found no association between montelukast use and neuropsychiatric adverse events (HR 0.99,95% CI 0.84-1.16) when compared to long-acting β-agonists 2
- However, a 2023 Danish nationwide study demonstrated a 14% increased risk of neuropsychiatric medication use (HR 1.14,95% CI 1.08-1.20), with the highest risk in younger adults aged 18-29 years 3
Clinical practice studies show higher rates than previously recognized:
- A 2022 prospective study found neuropsychiatric adverse reactions in 62.4% of children taking montelukast, with temperamental behavior, nightmares, and sleep disorders being most common 4
- Another 2022 study reported adverse reactions in 31.9% of children, with sleep disturbance (15.1%), agitation (10.4%), pain (9.4%), and hyperactivity (6.8%) being most frequent 5
Specific Neuropsychiatric Manifestations
The most commonly reported neuropsychiatric effects include:
- Sleep disturbances: Sleep difficulties, interruption, nightmares (15.1% in pediatric studies) 5
- Behavioral changes: Agitation (10.4%), hyperactivity (6.8%), temperamental behavior 5, 4
- Mood disorders: Anxiety (11% increased risk), depression 6
- Suicidal ideation: Rare but serious, prompting FDA warning 1
- Confusion and psychotic-like symptoms: Very rare 2
Age-Related Risk Patterns
Younger patients appear at higher risk:
- Children aged 4-9 years showed the highest prevalence of adverse reactions (52.8%) 5
- Young adults aged 18-29 years had significantly elevated risk (HR 1.28) for hospital contacts with neuropsychiatric diagnoses 3
- Risk decreases with increasing age across all studies 3
Common Non-Neuropsychiatric Side Effects
Guidelines consistently describe montelukast as having "minimal" or "no specific adverse effects" for routine side effects 7:
- Headache
- Gastrointestinal: Abdominal pain, nausea, thirst 1
- Somnolence (though less than first-generation antihistamines)
- Psychomotor hyperactivity 1
These effects are generally mild and well-tolerated 8.
Rare but Serious Adverse Events
Hepatotoxicity
Postmarketing surveillance has documented rare cases of liver injury 7:
- Reversible hepatitis
- Irreversible hepatic failure resulting in death and liver transplantation (extremely rare)
- Elevation of liver enzymes
This contrasts with zafirlukast (another leukotriene receptor antagonist), which requires hepatic enzyme monitoring 7.
Churg-Strauss Syndrome
Rare cases of systemic eosinophilia with vasculitis consistent with Churg-Strauss syndrome have been reported, usually associated with reduction of oral corticosteroid therapy 1. A causal relationship has not been established, as these patients often have severe asthma requiring multiple medications 7, 1.
Quality of Life Impact
Neuropsychiatric adverse reactions significantly impair quality of life when they occur:
- Both child-reported and parent-proxy quality of life scores decreased significantly in patients experiencing adverse reactions 4
- Children with adverse reactions had 2.66-6.43 times higher odds of decreased quality of life depending on age group 4
Clinical Implications for Prescribing
Given the FDA black box warning and emerging safety data, current practice emphasizes:
Patient selection: Consider montelukast when benefits clearly outweigh risks, particularly avoiding use for mild symptoms that can be adequately treated with other medications 1
Pre-treatment counseling: Patients must be instructed to notify prescribers immediately if neuropsychiatric changes occur 1
Monitoring: Prescribers should be alert for behavioral changes, mood alterations, sleep disturbances, and suicidal ideation 1
Discontinuation: Stop montelukast if neuropsychiatric events occur 1. Most adverse reactions resolve upon drug discontinuation 5, 4
Alternative therapies: The 2020 asthma guidelines note that montelukast has "increased risk of adverse consequences" making its use "less desirable" compared to alternatives 9
Overdose
Montelukast has a wide safety margin in overdose:
- Doses up to 1000 mg have been reported with minimal adverse effects 1
- Most overdose cases showed no adverse experiences or only mild symptoms (abdominal pain, somnolence, headache) 1
- No mortality occurred in animal studies at doses up to 5000 mg/kg 1
Context: Safety Relative to Efficacy
The safety profile must be weighed against modest efficacy:
- Montelukast is less effective than inhaled corticosteroids for asthma 8
- It is less effective than intranasal corticosteroids for allergic rhinitis 10
- Guidelines describe it as having "no significant difference in efficacy" compared to oral antihistamines 8
This risk-benefit calculation has led to montelukast being positioned as an alternative rather than preferred therapy in current guidelines 9, 10.