Interaction between cyclosporine and Hypericum perforatum (St. John's wort) after organ transplantation.

The use of herbal medicine has become increasingly popular in the United States. Hypericum perforatum (St. John's wort) is an herbal extract that is used widely as a folk remedy for depression. In this case report, we describe a kidney transplant recipient who developed marked reduction of cyclosporine therapeutic activity after the self-initiation of St. John's wort. Postulated mechanisms for the ability of this herbal extract to interact with pharmaceutical medications are presented, and the existing literature is reviewed.