1st generation antihistamine, ethanolamine, with moderate sedative and marked antimuscarinic effects. The latter could decrease prolactin production, which is important for milk production especially in the first few weeks. Their pharmacokinetic data (high volume of distribution and high percentage of plasma protein binding) explain the negligible excretion observed in milk (Kok 1982). However, there is a published case of a 10-week-old infant who showed signs of lethargy, irritability and rejection of feeding, although the mother took phenytoin and carbamazepine in addition to clemastine. No levels of clemastine were detected in the girl's plasma, who recovered well and continued to breastfeed (Kok 1982). Until there is more published data on this drug in relation to breastfeeding, safer known alternatives may be preferable, especially during the neonatal period and in case of prematurity. Lethargy and adequate feeding of the infant should be monitored. Co-sleeping with the baby is not recommended if this drug is being taken (UNICEF 2013, Landa 2012, ABM 2008, UNICEF 2006).