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Warwick, Australia Reports of possible herb/drug interactions involving St. John's wort (Hypericum perforatum) have prompted the Australian government to mandate label changes for products containing the popular antidepressant herb.
All manufacturers selling products in Australia must now include the following words on the label: "St. John's wort affects the way some prescription medicines work. Consult your doctor." There is no label change for products sold in the United States.
Some studies have demonstrated that hypericum increases the activity of cytochrome P450, thereby increasing the metabolism of some drugs. For instance, the Swedish Medical Products agency reports cases of decreased effectiveness of the anticoagulant drug warfarin in patients also taking St. John's wort.