Any medication used during pregnancy should always have a clear indication. On the other hand, any medication that is important for the mother should not be left unprescribed. Medication should be planned before pregnancy already, and drugs for which there is experience of use during pregnancy should be preferred. Susceptibility to malformations is at its highest from the beginning of the 5th to the end of the 10th week of pregnancy, counting from the last menstruation, i.e. from the 3rd to the 8th foetal week from conception. At later stages of pregnancy, adverse drug effects may manifest in other ways, such as delayed growth, disturbed organ maturation or, for instance, cognitive problems appearing later. The minimum dose that is sufficient for the treatment of the mother's symptoms should be used.. The same principles apply for breastfeeding.