For centuries, birthwort has been used in traditional medicine in China (and ancient Greece before that) to treat arthritis and ease childbirth, among other conditions. (The flower is shaped like a uterus.) Today aristolochic acid is found in supplements for weight loss, menstrual symptoms, and rheumatism. It’s widely used in Asia, where it’s added to medicinal wine, ointments, and diet pills. One study found that between 1997 and 2003, fully one-third of Taiwanese were prescribed birthwort supplements by a Chinese medicine practitioner.