Natural medicine, although it has been used for centuries, has only recently gained increasing interest and is treated as a remedy for all ailments. It is very often abused due to a lack of sufficient knowledge about potential adverse reactions and possible interactions between plant preparations and particular drugs. Moreover, traditional medicine used for a long period of time without restriction can lead to permanent damage to health and even death. This paper outlines the dangers of harmful effects of plant preparations when used inappropriately and when co-interacting substances are combined.