Abstract: The invention features methods of identifying a subject as being likely to have a positive therapeutic response to a psychedelic agent. Methods of the invention also include administering a psychedelic agent to a subject (e.g., a subject that has been identified as likely to respond positively thereto) to improve mental or physical well-being in the subject (e.g., by treating stress, anxiety, addiction, depression, compulsive behavior, by promoting weight loss, by improving mood, by treating or preventing a condition (e.g., psychological disorder), or by enhancing performance).