Breastfeeding is the most healthful method of feeding neonates and infants. In 2001 about 98% of new mothers in Lithuania started breastfeeding their neonates. One-third of nursing women (34%) discontinued breastfeeding at the time when infant reached the age of 3 months. About 56% of women breastfed their infants longer than 4 months. Only 3-6% of nursing women discontinued breastfeeding after the fourth month. Discontinuation of breastfeeding in 21-23% of all cases was directly or indirectly associated with use of medications. Such data suggest that there is a lack of information often leading physicians to advise mothers to discontinue breastfeeding because of medication use. The aim of this article was to survey the situation about classification of drugs used during breastfeeding and factors influencing drug transfer into milk in order to give more information for physician concerning the use of medication during breastfeeding. In this review, a short description of main pharmacokinetic characteristics, influencing drug transfer into milk; information on the classification of drugs used during breastfeeding; some considerations on drug safety and possible adverse effects of medications on breastfed infant; the list of drugs preferred for nursing women are presented.