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Review
. 2025 May 29;17(6):719.
doi: 10.3390/pharmaceutics17060719.

The Impact of Substance Use Disorder and Drug Transfer into Breast Milk: Implications for Maternal and Infant Health

Yongzong Yang  1 , Bofang Yi  2 , Tao Zhang  2
Affiliations
Review

The Impact of Substance Use Disorder and Drug Transfer into Breast Milk: Implications for Maternal and Infant Health

Yongzong Yang et al. Pharmaceutics. .

Abstract

Breast milk provides significant health benefits to both infants and mothers, offering protection against infections and enhancing cognitive development. This paper examines the complex effects of substance use disorder (SUD) during pregnancy and lactation, focusing on the pharmacokinetics of drug transfer into breast milk. It highlights the mechanisms by which drugs enter milk, emphasizing the roles of passive diffusion and active transport, particularly through breast cancer resistance protein (BCRP). The study explores the impact of various substances on fetal and infant health, with a focus on the relative infant dose (RID) and milk-to-plasma (MP) ratio as key metrics for assessing drug safety in breastfeeding. The findings underscore the need for careful evaluation of maternal drug use during lactation to balance the benefits of breastfeeding with potential risks.

Keywords: breast milk; breastfeeding safety; drug transfer; infant health; lactation; milk-to-plasma ratio; pharmacokinetics; relative infant dose; substance use disorder.

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Conflict of interest statement

All authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
Layered anatomical and molecular structure of the lactating mammary gland and key transporters involved in drug transfer. The mammary gland exhibits a hierarchical organization from lobes to alveoli to individual alveolar epithelial cells. Several membrane transporters regulate the movement of substances between maternal plasma and milk. Uptake transporters—including organic anion transporting polypeptide 1A2 (OATP1A2), organic anion transporting polypeptide 2B1 (OATP2B1), and organic cation transporter 1 (OCT1)—facilitate substrate entry into mammary epithelial cells. Efflux transporters—breast cancer resistance protein (BCRP), P-glycoprotein (P-gp), and multidrug resistance-associated protein 5 (MRP5)—mediate active transport of compounds into milk. These transporter systems collectively influence drug disposition in breast milk and potential infant exposure. (Created in BioRender. Yi, B. (2025) https://BioRender.com/o2moqhl).
Figure 2
Figure 2
SUD effects on pregnant and infant populations.
See this image and copyright information in PMC

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