How would a medical audience respond to a lecture that was completely devoid of content, yet delivered with authority by a convincing phony? The responses were overwhelmingly positive, writes Carl Elliott, professor at the Center for Bioethics at the University of Minnesota. He says it's not that doctors are too gullible but that modern medical knowledge is so specialized and opaque. So now Big Pharma uses the terms "thought leader" or "key opinion leader"— KOL for short — to transmit messages to their peers. KOLs are usually convincing, influential, and apparently independent experts. But how reliable and objective are their messages?