Prescription drug use in breastfeeding mothers and infant exposure: A register-based cohort study.

Aims: Breast milk is the optimal infant nutrition; however, many infants may be exposed to prescription drugs if used by their mothers during breastfeeding. The aim of this study was to evaluate the prevalence and patterns of prescription drug use among breastfeeding mothers and to assess the availability of relative infant dose information for these drugs.

Methods: This population-based cohort study was conducted using nationwide Danish register data from January 2006 to December 2022. All registered mother-infant pairs were included during periods of exclusive breastfeeding. The national health registers were used to identify live births, breastfeeding status and prescription drug use by mothers during exclusive breastfeeding.

Results: Among 534 080 exclusively breastfed infants, 290 845 (54.5%) were breastfed by mothers who used at least 1 prescription drug during the breastfeeding period. The drugs were primarily for haemorrhoids, contraception, infections and pain management. Among individual systemic drugs used during exclusive breastfeeding, 51.5% lacked information on relative infant dose.

Conclusions: This large-scale cohort study reveals a high prevalence of prescription drug use during exclusive breastfeeding, often involving drugs with unknown safety profiles regarding their transfer into human milk. These findings highlight the need for updated regulatory measures and increased efforts by pharmaceutical companies to ensure reliable infant safety data.