[St. John's wort: a pharmaceutical with potentially dangerous interactions].

Over-the-counter preparations of St. John's wort are widely used as 'natural' herbal medicine alternative to traditional antidepressants. The antidepressant effect has been shown in numerous placebo controlled studies. The mechanism of action is assumed to be at least in part, similar to conventional antidepressants, due to presynaptic serotonin reuptake inhibition as well as GABA-modulation and inhibition of monoaminoxidases. Because of its favorable safety profile compared to conventional antidepressants, the use of St. John's wort preparations has gained high acceptance with doctors and patients. However, any biologically active compound contains a certain risk of untoward effects and/or interactions which often are neither known nor recognised with the use of herbal remedies. Thus, doctors, pharmacists, and patients might feel themselves in false safety. Recently, a variety of case reports of potentially hazardous interactions due to drug combinations with St. John's wort have been published (e.g. cellular rejection of pancreas-, kidney- as well as heart transplants with ciclosporin therapy, rise of INR with oral anticoagulants, bleeding with oral contraceptives, reduction of plasma concentration of digoxin, indinavir, amitriptyline, and theophylline). We report a case of irregular bleeding with oral contraception and discuss these drug interactions and the mechanisms.