Macrolide immunosuppressant drug that inhibits calcineurin which is used to prevent rejection of transplanted organs (kidney, liver, heart ...) and for treatment of atopic eczema, psoriasis and other autoimmune illnesses (e.g. Arthritis, Lupus, Inflammatory Bowel Disease ...) .Routes of administration: oral for systemic purposes and topical for dermatologic conditions. A high molecular weight and high protein-binding capacity explain that it is was found in clinically insignificant amounts into colostrum and breast milk (Jain 1997, 2003 French, Gardiner 2006, 2013 Zheng, Bramham 2013).No problems were observed on short or long term of developmental or immunological outcomes in more than 150 infants whose mothers were treated (French 2003, Gouraud 2012, Thiagarajan 2013, Constantinescu 2014, Izumi 2014), except a mild and self-limited case of transient thrombocytosis (Gouraud 2012).The plasma levels of drug in these infants were either undetectable or very low (Gomez-Lobo 2012, Gouraud 2012, Bramham 2013, Izumi 2014).A low oral bioavailability that may further be decreased by ingestion of food, especially if it is fat food, would hamper the passage of drug from ingested milk toward the infant plasma. Infants who have been exposed to calcineurin inhibitors during pregnancy may be immunological deficients within the first year of life (Grimer 2007), therefore, it is most important to avoid any lack of breastfeeding without a sound reason. Several medical societies and consensus by experts have considered safe the use of Tacrolimus while breastfeeding (Østensen 2006, van der Houde 2010, Thiagarajan 2013, Armenti 2013, Constantinescu 2014, Schulze 2014, Durst 2015, Götestam-Skorpen 2016, Flint 2016).