Omeprazole

Pregnancy

Birth defects: The PRILOSEC label says first-trimester epidemiologic data do not show an increased risk. Källén 2001, a Swedish omeprazole registry cohort, included 955 exposed infants. Five were stillborn and congenital heart defects were slightly more frequent, but the author said both findings could be random. Diav-Citrin 2005 followed 295 omeprazole-exposed pregnancies, including 233 first-trimester exposures; major anomalies occurred in 9 of 249 births (3.6%), compared with 30 of 792 control births (3.8%). Pasternak and Hviid 2010 studied 840,968 live births and 5,082 PPI exposures; first-trimester PPI exposure was not significantly associated with major birth defects, and no individual PPI showed a significant increase. Peron 2023 pooled 11 observational studies and 5,618 first-trimester PPI exposures; it found no significant increase in overall malformations (OR 1.10, 95% CI 0.95 to 1.26) or reported specific outcomes, but had insufficient data to assess omeprazole separately. Pregnancy outcomes: Breddels 2022 included 1,089,514 Swedish live singleton births and 14,787 PPI users. PPI-class use was associated with higher odds of preeclampsia (OR 1.19), gestational diabetes (OR 1.29), preterm birth (OR 1.23), and small-for-gestational-age birth (OR 1.27). This was not omeprazole-specific; PPI users had more obesity, comorbidities, and other medication use, and the authors said causality could not be established. Recent reporting studies: Dong 2025 found FAERS reporting signals for omeprazole and postpartum hemorrhage (ROR 3.14), fetal growth restriction (ROR 2.14), and preeclampsia (ROR 1.95). The authors called these signals exploratory and requiring confirmation. Zheng 2025 reported a possible omeprazole signal for gastrointestinal malformations in neonatal FAERS reports. The study had no exposed-pregnancy denominator, so absolute risk and causality cannot be estimated. Hong 2026 studied 2,777,119 South Korean children exposed to prenatal acid-suppressive medicines, not omeprazole alone. Small associations with ADHD, autism, intellectual disability, severe neuropsychiatric disorder, and obsessive-compulsive disorder appeared in weighted analyses, but sibling comparisons found no significant associations; the authors said shared familial factors may explain the weighted-model findings.

Breastfeeding

LactMed reports one mother taking 20 mg of omeprazole daily. Milk levels peaked at 20 mcg/L three hours after the dose, and LactMed estimated that an exclusively breastfed infant would receive about 0.9% of the maternal weight-adjusted dose. Published infant blood levels were not found. LactMed reports that the infant breastfed for three months while the mother took omeprazole and remained well at 12 months. Marshall 1998, the primary case report, measured a peak milk concentration less than 7% of peak maternal serum concentration. This evidence comes from one mother-infant case, not a larger outcome study. NHS SPS says omeprazole is a preferred PPI during breastfeeding, with recommendations for full-term, healthy infants. MotherToBaby also describes low milk levels in limited data. The PRILOSEC label says clinical infant-effect and milk-production data are not available; the ZEGERID label says published data suggest both omeprazole and sodium bicarbonate may be present in milk and also notes a lack of clinical infant-effect data.

What was tested

Human pregnancy evidence includes registry cohorts, prospective observational studies, a systematic review and meta-analysis, and spontaneous adverse-event reports. No randomized trial of omeprazole use in pregnancy was found in the reviewed sources. Most studies are observational; the Swedish pregnancy cohort and the recent reporting analyses cannot establish that omeprazole caused an outcome. The breastfeeding evidence includes one milk-level case report and one infant follow-up; published infant blood levels were not found, and the labels report no clinical data on milk production or infant effects.