Psychotherapy was the treatment of mental disorders by using non-medical means. The term became most popular in the 20th century and onward.
The rehab colony on Tantalus V in the 23rd century used psychotherapy in the form of an experimental neural neutralizer. In 2266, after Dr. Tristan Adams expressed his belief that a person who had moved on from their past insanity had no need for their memories of same, Helen Noel agreed that the shifting of memory patterns was basic to psychotherapy. (TOS: "Dagger of the Mind")