Immunosuppressant which is an inhibitor of calcineurin and used in the prevention of transplanted organ rejection (kidney, liver, heart ...) and in the treatment of severe forms of autoimmune diseases: Atopic Eczema, Psoriasis, Rheumatoid Arthritis, Ulcerative Colitis, Aplastic Anemia, Asthma, Behçet's Syndrome, Chronic Active Hepatitis, Multiple Sclerosis, Myasthenia Gravis, Sarcoidosis, Scleritis or Uveitis and Scleroderma, among others.Orally administrated for systemic use in one or two daily doses, parenteral injection, eye drops and inhalation. Its high molecular weight and high protein-binding capacity explain the low excretion (<0.36 mg / L) obtained in colostrum and mature breastmilk (Lewis 1983, Flechner 1985, Ziegenhagen 1988, Behrens 1989, Thiru 1997, Nyberg 1998, Munoz-Flores 2001, Moretti 2003, Osadchy 2011, Mazzuoccolo 2014).No short or long term issues on developmental or immunological response have been observed in infants whose mothers were taking this drug (Nyberg 1998, Munoz-Flores2001, Moretti 2003, Lahiff 2011, Morton2011).Plasma levels in most of these infants were undetectable or very low (Ziegenhagen 1988, Nyberg 1998, Munoz-Flores 2001, Moretti 2003, Osadchy 2011, Lahiff 2011, Morton2011). Only one exception has been reported who presented therapeutic levels (Moretti 2003). Its low oral bioavailability, even lower when taken along with food, mostly fatty food, would decrease the passage to infant's plasma from the ingested breastmilk. Although thought to be high, the total amount of alcohol contained in each dose of drug is considered not enough to contraindicate this medication during breastfeeding.There are isolated reports which indicate that cyclosporine may decrease prolactin levels (Ramirez 1991, Nagar 1992).Infants who have been exposed to calcineurin inhibitors during pregnancy may have immunized deficiency in the first year of life (Grimer 2007), hence the importance of not being deprived of breastfeeding for no proven reason. Several medical societies and experts agree that the use of this medication during breastfeeding is safe (van der Houde 2010, Thiagarajan 2013, Constantinescu 2014, Götestam-Skorpen 2016, Flint 2016).