It is excreted into breast milk in amounts that may be clinically significant and can be as high as a half of that reached in mother’s plasma and up to one third of the therapeutic level in the infant. In infants and newborns (5 days), premature babies and dehydrated or infected infants, who may show reduced clearance mechanisms for lithium, there have been reports of clear signs of lithium toxicity caused by ingestion of breast milk: cyanosis, lethargy, hypotonia or slight increase in TSH. However, there are numerous cases of infants whose mothers were on lithium who did not show any clinical, growth or neurodevelopmental problem at the short or long term. Breastfeeding is less risky for healthy term infants whose mothers are treated with lithium when she or her family has capacity enough to monitor the occurrence of adverse effects, medical supervision and, whenever necessary, monitoring of lithium levels in the mother-infant dyad. Mothers should stop taking lithium 1 to 2 days before delivery or cesarean section in order to decrease plasma levels in the newborn. Lithium may be, or not, a cause of increased Prolactin and galactorrhea.