Our brains are the substrate of all thought, emotion and behavior. Because our brains are the most complex objects of human inquiry, brain science is still at a relatively early stage of its development. Nonetheless, success in influencing brain function is already raising significant social, ethical and policy issues. Here, I highlight concerns related to one aspect of clinical neuroscience: the use of psychotherapeutic drugs, originally developed to treat illness, for individuals who are not ill. I focus on this issue, sometimes described as the use of drugs for ‘enhancement’ of normal function, because it is already upon us even as science is focused on the development of safer and more effective drugs for an expanding list of indications related to alertness, mood and cognition.