Can Montelukast Cause Tiredness?
Yes, montelukast can cause tiredness and drowsiness, though this is not among its most commonly reported side effects. The FDA drug label explicitly lists drowsiness as an adverse reaction, and recent clinical evidence demonstrates that montelukast can paradoxically both improve and worsen sleep-related symptoms depending on the clinical context 1.
Direct Evidence of Drowsiness
The FDA-approved drug label for montelukast specifically lists "drowsiness" among its adverse reactions, appearing in the post-marketing surveillance data for psychiatric and nervous system disorders 1.
Somnolence (sleepiness/drowsiness) has been reported in clinical trials, though the incidence was similar to placebo in controlled studies of allergic rhinitis 1.
Sleep Disturbances as the Primary Concern
The relationship between montelukast and tiredness is more complex than simple drowsiness:
Sleep disturbances are the most frequently reported adverse effect in pediatric populations, affecting 15.1% of children in a large retrospective study, with 5.5% experiencing sleep difficulties and 4.4% experiencing sleep interruption and decreased sleep 2.
In infants and young children (under 2 years), sleep disorders are the predominant neuropsychiatric symptom, while older children and adolescents more commonly experience depression, anxiety, and behavioral changes 3.
A recent 2025 cohort study of 1,163 children found significant increases in drowsiness after montelukast treatment, with overall neuropsychiatric symptoms increasing from 14.8% to 34.3% after one month of treatment 4.
Paradoxical Effects on Daytime Fatigue
Interestingly, montelukast can have opposing effects depending on the underlying condition:
In adults with perennial allergic rhinitis, montelukast actually reduced daytime somnolence and fatigue compared to placebo (p = 0.0089 for somnolence, p = 0.0087 for fatigue), likely by improving nasal congestion and sleep quality 5.
This suggests that when montelukast effectively treats the underlying allergic condition, it may improve rather than worsen daytime tiredness 5.
Clinical Implications and Monitoring
The European Respiratory Society recommends active surveillance for sleep disturbances at each follow-up visit, as these are among the key neuropsychiatric adverse events associated with montelukast 6.
Patients should be instructed to immediately notify their prescriber if sleep disturbances or excessive drowsiness develop 6.
The FDA issued a black box warning regarding neuropsychiatric events, which includes sleep-related symptoms, emphasizing the need for careful monitoring when initiating therapy 7.
Montelukast should be discontinued immediately if significant sleep disturbances or dream abnormalities develop 6.
Risk Factors
Concomitant use of antihistamines increases the risk of neuropsychiatric symptoms and sleep disorders in children treated with montelukast 4.
Children aged 4-9 years appear to be at highest risk for adverse drug reactions (52.8% of reported cases), followed by adolescents (24.4%) 2.
Practical Recommendations
The American Academy of Pediatrics recommends taking montelukast in the evening or at bedtime, which may be relevant if drowsiness occurs, as this timing could minimize daytime impairment 7.
Given that montelukast is not recommended as first-line therapy and should only be considered when patients do not tolerate nasal corticosteroids, the risk-benefit ratio should be carefully evaluated 6.
If tiredness or sleep disturbances develop, consider switching to alternative therapies such as inhaled corticosteroids, which have superior efficacy profiles without these specific neuropsychiatric risks 6.