PURPOSE: There is a dearth of information on maternal drug exposure during lactation. The Korean Mothersafe Professional Counseling Center launched helpline to provide information and clinical consultation service on drug safety during lactation as well as in pregnancy. Here, we reviewed our 5 years' experience of counseling with drug exposed breastfeeding mothers. METHODS: The questionnaires were given to drug exposed breastfeeding mothers from January 2005 to April 2010 who contacted our helpline and follow-up survey data was collected by phone call. The questionnaires included lists of symptoms that exposed mothers experienced and that was observed in their infants, as well as demographic questions and questions about lactation. RESULTS: A total of 278 mothers completed the survey and lactational exposure was estimated. Majority of them reported that their infants and themselves never experienced serious side effects of drugs during lactation. Only 3 (1.1%) babies reported side effects and 20 (7.2%) mothers reported decreased production of breast milk. Two hundred thirty two (83.5%) mothers continued breastfeeding after counseling. Lactation was stopped temporarily in 20 (7.2%) mothers and permanently in 26 (9.3%) mothers. CONCLUSION: Most of the drugs exposed during lactation did not cause serious side effects to infants and mothers. As many drugs have inadequate data to assure safety, the clinician is left with a dilemma as to where the balance of risks and benefits lie with respect to the mother and her baby. The author expect that analyses of these counseling will contribute to provide practical answers to clinicians as well as exposed mothers and to establish correct breastfeeding practice.