Pro. Dr. Gessmann received a doctorate in 1976 by his work about causation factors of Dyslexia. He is the founder of humanistic psychodrama and adopted in the same year for the first time psychodrama with hypnosis in the context of sexual dysfunctions. In the last twenty years he concentrated on diagnosis and therapy of transgender people and is in Germany accepted as a court expert. He also established humanistic psychodrama in the field of child psychotherapy. In the early 80s he began making film-documentations about complete group-psychotherapy-sessions in European countries. He is the publisher of book series and the International Journal of Humanistic Psychodrama. Pro. Dr. Gessmann is one of the few empirical researchers in the field of psychodrama and has published over 180 articles on psychological topics.
In 1973 he founded the Psychotherapeutisches Institut Bergerhausen (PIB) in Duisburg and in 1977 nearby Kerpen, Germany a European training center now for more than 1500 psychotherapists.
In 1986, Pro. Dr. Gessmann founded Germany’s first home-based sleep laboratory with the Department of Sleep Medicine. From 1998 to 2002, under his guidance, the tongue muscle training with the registered trademark ZMT ® was developed as an alternative treatment against sleep apnea.
Pro. Dr. Gessmann developed and has taught humanistic psychodrama since 1979 as a new form of psychodrama. It became an integral part of humanistic psychology. Pro. Dr. Gessmann moved the collective action and nature of the people at the center of the therapeutic ethic. Faith, love, hope, and the idea of a human community are essential to meaningful humanistic psychodrama. Through his work in many countries and with many different people of different ages, he was able to gain extensive experience, which in turn was very helpful for his future work.
Pro. Dr. Gessmann is a member of the American Society of Group Psychotherapy and Psychodrama as well as the International Association of Group Psychotherapy and Psychodrama since 1977.