IBCLC Practice Exam 2025 – Complete Preparation Guide

The primary means by which drugs transfer from maternal plasma into breast milk is through simple diffusion. This process involves the movement of molecules from an area of higher concentration (such as maternal plasma) to an area of lower concentration (breast milk). Because breast milk is produced in the mammary glands, the concentration of drugs in maternal plasma affects how much of that drug becomes present in the milk.

Drugs that are small, uncharged, and lipophilic (fat-soluble) are particularly likely to passively diffuse into breast milk. This characteristic makes simple diffusion the most common mechanism for drug transfer rather than active transport, which requires energy and is typically used for transferring nutrients against a concentration gradient, or filtration and endocytosis, which involve other specific cellular mechanisms that don’t apply as broadly to the transfer of most drugs into breast milk.

Understanding this process is essential for lactation consultants when advising breastfeeding mothers on medication use, as it allows for informed decisions regarding drug safety in lactation.