Charles P. O'Brien (born August 20, 1939, in New Orleans, Louisiana) is a veteran addiction researcher, prominent research scientist, medical educator, psychiatrist, physician, neurophysiologist, and university teacher specializing in the science and treatment of addiction. He is board-certified in neurology, psychiatry, and addiction psychiatry. O'Brien serves as the Kenneth E. Appel Professor of Psychiatry and vice chair of psychiatry at the Perelman School of Medicine at the University of Pennsylvania, where he is also recognized as Emeritus Professor of Psychiatry. He has been a long-time Chief of Psychiatry and Director of the Penn Center for Studies of Addiction (now Center for Studies of Addictions), contributing extensively to the field with over 553 publications and more than 53,000 citations. He has collaborated professionally with figures such as Miriam Adelson on projects related to addiction studies and has affiliations with the University of Pennsylvania, including election to prestigious bodies.