Can montelukast (Singulair) cause tiredness?

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 and somnolence as adverse reactions, and 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" as a reported adverse reaction in post-marketing surveillance 1
• Somnolence is documented in the official prescribing information, though the incidence was similar to placebo in controlled clinical trials 1
• In overdose reports (doses up to 1000 mg), somnolence was among the most frequently occurring adverse experiences 1

Sleep Disturbances Leading to Fatigue

The relationship between montelukast and tiredness is complex, as the medication can cause various sleep disturbances that secondarily result in daytime fatigue:

• Sleep disturbances are the most common neuropsychiatric adverse reaction to montelukast, affecting 15.1% of pediatric patients in a large retrospective study 2
• Sleep difficulties included sleep interruption, decreased sleep quality, and nightmares, all of which can manifest as daytime tiredness 2
• A 2025 cohort study of 1,163 children found significant increases in drowsiness after 1 month of montelukast treatment compared to baseline (p < 0.001) 3

Paradoxical Effects on Daytime Somnolence

Interestingly, montelukast shows contradictory effects depending on the underlying condition:

• In patients with perennial allergic rhinitis, montelukast actually improved daytime somnolence (p = 0.0089) and daytime fatigue (p = 0.0087) compared to placebo by reducing nasal congestion and improving sleep quality 4
• This suggests that when tiredness is caused by the underlying allergic condition disrupting sleep, montelukast may help rather than worsen fatigue 4
• However, as a direct adverse effect independent of disease improvement, drowsiness and sleep disturbances can occur 1, 2

Age-Related Patterns

• Infants and young children (under 2 years) primarily experience sleep disorders as their main psychiatric adverse reaction 5
• Children aged 2-11 years report sleep disturbances along with depression/anxiety symptoms 5
• The 2021 Spanish case series found insomnia was the most common adverse reaction (7 out of 20 patients with ADRs), appearing from the first days to months after starting treatment 6

Clinical Implications

• The FDA issued a black box warning regarding neuropsychiatric events including sleep disturbances, and patients should be monitored for unusual symptoms when starting montelukast 7, 8
• The European Respiratory Society recommends active surveillance for sleep disturbances at each follow-up visit 9
• If significant sleep disturbances or drowsiness develop, montelukast should be discontinued immediately 9
• The American Academy of Pediatrics recommends taking montelukast in the evening or at bedtime, which may be relevant given its potential to cause drowsiness 7

Important Caveats

• While drowsiness is listed as an adverse reaction, it was not significantly more common than placebo in controlled trials, suggesting the true incidence may be relatively low in the general population 1
• Real-world post-marketing data and observational studies suggest higher rates of sleep-related adverse effects than initially detected in clinical trials 2, 5, 3
• Concomitant use of antihistamines with montelukast increases the risk of neuropsychiatric symptoms including drowsiness 3