Prescribing medications for a breast-feeding mother requires weighing the benefits of medication use for the mother against the risk of not breast-feeding the infant or the potential risk of exposing the infant to medications. A drug that is safe for use during pregnancy may not be safe for the nursing infant. The transfer of medications into breast milk depends on a concentration gradient that allows passive diffusion of nonionized, non-protein-bound drugs. The infant's medication exposure can be limited by prescribing medications to the breast-feeding mother that are poorly absorbed orally, by avoiding breast-feeding during times of peak maternal serum drug concentration and by prescribing topical therapy when possible. Mothers of premature or otherwise compromised infants may require altered dosing to avoid drug accumulation and toxicity in these infants. The most accurate and up-to-date sources of information, including Internet resources and telephone consultations, should be used.