The types and rate of adverse drug reactions experienced by breastfed infants whose mothers are taking medications has not been well defined. This article reviews the literature on adverse drug reactions in infants since a previous review in 2002. Case reports and studies of adverse drug reactions in breastfed infants whose mothers were taking a prescribed or over-the-counter medication were selected. Fifty-three case reports and 16 studies were located. Serious acute adverse drug reactions from drugs in breastmilk appear to be uncommon. Infants under 2 months of age, and especially those under 1 month, appear to be most susceptible. Similar to previous reviews, free iodine, opioids, and the use of multiple central nervous system drugs simultaneously were identified as drugs of concern. A few narrowly focused studies are now available on long-term effects of maternal drug therapy on breastfed infants and they are mostly reassuring.