John J. Ratey, M.D.,(born April 7, 1948) is associate clinical professor of psychiatry at Harvard Medical School.
He is the coauthor, with Edward Hallowell of the books Driven to Distraction, Answers to Distraction, and Delivered from Distraction. He is also the author of Shadow Syndromes. In 2001 he published the book A User's Guide to the Brain, in which he describes the human brain as a flexible muscle, which works on a "use it or lose it" basis. He is the author of Spark: The Revolutionary New Science of Exercise and the Brain (2008), which describes the positive benefits that exercise can have for people with ADHD.