At present the use of medicaments of plant origin is on the increase. It is therefore necessary to take into consideration that there exist known as well as potential interactions between the medicament of the medicinal plant. The problematic plants include Echinacea, Allium cepa, Gingko biloba, Panax ginseng, as well as Hypericum perforatum, Valeriana officinalis, or Glycyrrhiza glabra. Its use should be limited, or completely excluded in the cases of simultaneous therapy with, e.g., warfarin, hepatotoxically acting medicaments, MAOI inhibitors, phenelzin sulphate, or phenytoin, as they may decrease of completely eliminate the therapeutic effect of the administered drugs, or they may cause a toxic damage to the organism.

        Key words: medicinal plant – drug – interaction