Drug use during pregnancy is an important issue that is closely related to the health of both the mother and the fetus. Drug type, dose, receiving frequency, the placenta and breast milk passage, drug distribution, metabolism, which was received with other drugs, each fetus response to drugs, the fetus age, maternal health and nutrition are characteristics that determine their effects on the fetus of drugs. Various classification systems have been developed for the effects of drugs on the fetus and it has been determined that there are differences in the classification of some agents among the classification systems. It is necessary for the health personnel to improve and update the information in this area. This article explains drug interactions in pregnancy, drug classification systems and counseling.