The growing knowledge of St. John's wort (Hypericum perforatum L) drug interactions and their clinical significance

Objective: This review discusses drug interactions with St. John's wort (Hypericum perforatum L), and their clinical relevance. Background: Herbal medicines are being used by an increasing number of patients who typically do not inform their clinicians of concomitant use. Recent reports indicate that St. John's wort extracts may potentiate certain subenzymes of the cytochrome P-450 enzyme system. This may decrease the serum concentration of a number of concomitant drugs, including warfarin, digoxin, theophylline, cyclosporin, and oral contraceptives. Several common foods and drinks leg, broccoli, red nine) also influence parts of this same enzyme system. Well-documented cases concern 24 subjects (including 8 healthy volunteers) of millions of people treated with Hypericum extracts, thus showing a strong underreporting of the effects and safety of herbal medicines. Conclusion: Although evidence is growing on the effectiveness of Hypericum in mild to moderate depression, and its safety has been established in double-blind, randomized clinical trials, pharmacovigilance is needed for all herbal medicines, and a tighter regulatory framework is desirable. Regulatory agencies in the United States and Europe have already issued warnings about Hypericum drug interactions.