[Phytotherapy threats with emphasis on St. John's wort medicines].

: Plant medicines used by patients in self-treatment contain powerfully acting active substances which can be a source of adverse events including interactions with synthetic medicines. Usage of St. John's wort causes high risk of various complications. St. John's wort preparations shouldn't be combined with antidepressants without physician's consultation. Long-term intake of medicines which contain Hypericum perforatum extracts can be a reason of undesirable interactions with isoenzymes CYP3A4, CYP1A2, CYP2C9, CYP2C19 and P-glycoprotein (P-gp) for which St John's wort is a substrate. Compounds present in the St. John's wort, especially hyperforin, increase the activity of cytochrome P450 in the liver and intestinal mucosa as well as P-gp, which can accelerate their elimination from the body, decrease their concentrations and reduce the effect. Effective and safe phytotherapy requires a lot of knowledge about the properties and toxicity of preparations used and accurate monitoring of the consequences of their actions.