LactMed, part of the National Library of Medicine’s (NLM) Toxicology Data Network (TOXNET®), is a database of drugs and dietary supplements that may affect breastfeeding. It includes information on the levels of such substances in breast milk and infant blood, and possible adverse effects in the nursing infant. Suggested therapeutic alternatives to those drugs are provided, where appropriate. All data are derived from the scientific literature and fully referenced. Summaries of the reported information are provided and include links to other NLM databases. Supplemental links to breastfeeding resources from credible organizations are also provided.