[1][2] Medications, when administered to breastfeeding mothers, almost always are transferred to breast milk, albeit usually in small quantities.
[3] The degree of impact on the nursing infant varies, with many medications posing minimal risk.
The National Institutes of Health (NIH) maintains a database, which contains information on drugs and other chemicals to which breastfeeding mothers may be exposed.
[5] The determination of the safety of a medication can be evaluated by considering the following: Drugs can be categorised in one of five categories to determine how safe they are for breastfeeding:[6][7][8][9] "Drug which has been taken by a large number of breastfeeding mothers without any observed increase in adverse effects in the infant.
"[6] "Drug which has been studied in a limited number of breastfeeding women without an increase in adverse effects in the infant.
)"[6] "There is positive evidence of risk to a breastfed infant or to breastmilk production, but the benefits of use in breastfeeding mothers may be acceptable despite the risk to the infant (e.g. if the drug is needed in a life-threatening situation or for a serious disease for which safer drugs cannot be used or are ineffective).