Epimedium, also known as barrenwort, bishop's hat, fairy wings, horny goat weed, rowdy lamb herb, randy beef grass or yin yang huo, is a flowering plant endemic to China. It has been present in Traditional Chinese Medicine for centuries as a remedy for low libido, erectile dysfunction, fatigue, pain, and other conditions. According to recent studies, epimedium contains icariin, which is a PDE5 inhibitor. Icariin causes more blood to flow to the penis and could theoretically work better and cause fewer side effects than current drugs for erectile dysfunction. Animal, human, and in vitro studies indicate that icariin also stimulates osteoblast activity in bone tissue, and therefore can treat osteoporosis.