I believe there are psychotherapy cults. Those therapies that qualify have many of the earmarks of cults and mind control, thought reform, & brainwashing organizations.
All that’s needed is a charismatic/all knowing leader (therapist), devotees (patients/clients), a belief system and the vulnerability and openness to change one’s thinking, or old way of being which is then replaced with an abuse narrative.
The link below is a lecture by Robert J. Lifton who studied mind control & brainwashing in the 1950s. For more information on his publications, please refer to the Reading list – books page
Robert J. Lifton, On Destructive Cults Lecture Retrieved from YouTube 4/2/11.