Historians avoid studying the efficacy of therapy before the age of the double-blind randomised trial. A related topic that has been the cause of great confusion is the meaning of the placebo effect and the efficacy of placebos. Medical anthropology and sociology, although they do not usually study the past, offer extremely useful tools for dealing rationally with both issues. This study uses their methods, among others, to argue that the body’s response to specific therapy is only one component of understanding efficacy, and that the others are much more useful in historical studies, especially those of other cultures. The case studies given in this paper are based on largely medical texts from sixteenth- to seventeenth-century China.