Montelukast

Pregnancy

Pregnancy evidence is observational and does not establish cause. For major birth defects, MotherToBaby reports that medical-record reviews and smaller studies have not found an increased chance. Fareed et al. 2024 pooled study results and reported no statistically significant increase in major congenital anomalies (RR 1.13, 95% CI 0.74-1.73), but reported an association with low birth weight (OR 1.82, 95% CI 1.35-2.45) and possible preterm delivery; the miscarriage estimate was inconclusive (OR 1.03, 95% CI 0.72-1.50, I-squared 73%). Jiao et al. 2026 studied 44,435 pregnancies with first-trimester controller prescriptions and found no increased overall major-malformation risk across five regimens; a montelukast plus inhaled-corticosteroid group had a cleft lip or palate signal based on fewer than five events. This cohort included singleton live births, so it does not resolve pregnancy loss or later-trimester outcomes. Hatakeyama et al. 2022 reported a mixed LTRA cohort of 231 exposed pregnancies (122 montelukast, 106 pranlukast, 3 both) and 212 live births; the anomaly rate was 1.9%, with no significant group differences in miscarriage, stillbirth, preterm birth, or low birth weight. Cavero-Carbonell et al. 2017 analyzed 754,300 singleton pregnancies, including 401 montelukast-only and 426 montelukast-plus-other-asthma-medicine pregnancies; no significant major-anomaly increase was found, while preterm birth, preeclampsia, and gestational diabetes associations were reported. Bakhireva et al. 2007 included 96 LTRA exposures (montelukast or zafirlukast); the defect rate was higher than in non-asthma controls but not asthma controls, without a consistent pattern. Sarkar et al. 2009 followed 180 montelukast-exposed pregnancies, including 160 live births, 20 spontaneous abortions, two elective terminations, and one major malformation; mean birth weight was lower than in both comparator groups, while the authors considered asthma severity a likely explanation. The studies vary in drug exposure, comparator groups, and outcome coverage. Confounding by asthma severity, co-medication, and prescription-based exposure remains important.

Breastfeeding

Datta et al. 2017 measured montelukast in milk from seven breastfeeding mothers after a single 10 mg dose. The average milk level was 5.3 ng/mL, the peak was 9.7 ng/mL at four hours, and the estimated relative infant dose was 0.68% of the maternal dose adjusted for weight. This was a small pharmacokinetic study and did not measure infant blood levels or clinical outcomes. LactMed's page, last revised July 15, 2024, reports that relevant published infant-level and infant-effect information was not found as of that date. LactMed cites international guidance that considers leukotriene receptor antagonists usable during breastfeeding. NHS guidance says use can be considered if the baby is healthy, while UK product information says use only if clearly essential and states that human-milk excretion is unknown. The FDA label acknowledges a published human-milk study, says available data do not suggest a significant risk of infant reactions, and states that effects on milk production are unknown. The evidence supports low measured transfer, but direct infant-outcome evidence remains absent in the reviewed sources.

What was tested

The pregnancy literature includes prospective and retrospective cohorts, prescription-registry studies, and a 2024 meta-analysis. The newest first-trimester cohort compared five controller regimens among 44,435 singleton live births to mothers with asthma; its cleft lip or palate finding for montelukast plus inhaled corticosteroids was based on fewer than five events. The 2022 Japanese cohort combined montelukast and pranlukast and therefore is not a montelukast-only estimate. The 2007 Bakhireva study also combined montelukast and zafirlukast. The 2017 Danish study included both montelukast-only and combination-exposure groups. The small 2017 lactation study measured milk concentrations after one maternal dose, not infant outcomes. Tsai et al. 2023 studied LTRA-class exposure during pregnancy, not montelukast alone; among 1,988 exposed children and 19,863 matched controls, it found no statistically significant association with ADHD, autism spectrum disorder, or Tourette syndrome, but follow-up and generalizability were limited. A 2026 cohort of children treated for asthma after birth compared montelukast with inhaled corticosteroids; it concerns postnatal use and does not estimate prenatal exposure effects.