The author shares her experience which she has gathered in the course of her long-time therapeutic practice of treating female patients with anorexia nervosa. She refers to the differentiation made by Seligman between efficacy studies and effectiveness studies in psychotherapy. She also considers the possibility of conducting research in the context of a complementary and complex therapeutic process. The complementarity of psychotherapy consists in the application of the systemic approach and elements of the cognitive-behavioural approach at respective stages of the therapeutic process, as well as the application of individual and family psychotherapy. In the article, the author describes the psychotherapy of people with anorexia nervosa treated on an outpatient basis between 2003–2019. The therapy was conducted individually and on a family basis. In the last 16 years, this psychotherapy has been applied to 475 Polish female patients aged 11–25. In the course of her therapeutic and clinical practice, and based on her gathered experience, the author has developed a therapeutic treatment which gives broadly understood positive effects. As regards research in psychotherapy, the author poses the following questions: Could one conduct research in psychotherapy which integrates various forms and paradigms? If yes – how? How to isolate and include a non-specific factor (the therapist) in such research? How to determine extra-therapeutic factors influencing the cognitive and intellectual processes of a person (people, in the case of family therapy) who is undergoing therapy? Is it possible to include the therapeutic influences described above in the Integrated Qualification System?