Dr Cheng's comments regarding potential drug interactions with St John's wort are very important. Since the publication of our review, substantial evidence has arisen suggesting that St John's wort induces cytochrome p450, thereby potentially lowering the serum levels of many drugs. Those with a very narrow therapeutic window, such as the protease inhibitors used to treat human immunodeficiency virus infection, are of special concern.1 Regarding hyperforin, Hypericum extract contains at least 10 substances that have been shown to have biological activity, including hyperforin. Like hyperforin, several of these substances have been shown to bind neuroreceptors in the brain and to inhibit the uptake of various neurotransmitters thought to be involved in depression.
Gaster B. Hyperforin in Extracts of St John's Wort (Hypericum perforatum) for Depression—Reply. Arch Intern Med. 2000;160(16):2546. doi: