In 1984, he completed his habilitation for clinical psychology at Ludwig-Maximilians-University Munich with publication and a monograph on "Course and Outcome of Treated and Untreated Anxiety and Depressive Disorders".
Throughout his professional career, Wittchen repeatedly was "visiting scientist" and "visiting professor" at the National Institute of Mental Health, Bethesda, USA, at the University of Michigan in Ann Arbor, USA and the Harvard University in Boston (US), where he collaborated with Lee Robins, Ron Kessler and Darrel Regier on the development of diagnostic tools and national and international epidemiological surveys.
They also led to subsequent studies in which he explored the role of stress, trauma PTSD and substance use as well as the impact of mental disorders on neurological and somatic disease.
He also was PI and Co-PI on a number of studies on the prevalence, effects, course, care, therapy, and prevention of mental disorders in Germany and worldwide.
[9] With over 840 (2018) peer review publications, he has been awarded the status of “Highly Cited” in Web of Science since the late 90's and is listed by Thomson Reuters among the World's Most Influential Scientific Minds (2015).
In 2019, Buzzfeed News Germany published allegations that Wittchen had ordered junior colleagues to fabricate data in a 2016–2018 survey of German psychiatric facilities.
The investigatory commission's report indicated that Wittchen had ordered colleagues to fabricate data for 20 (of 93) facilities surveyed in the study, and had afterwards sought to conceal the manipulation by altering documents and intimidating whistleblowers and university administrators.
[12] Wittchen is or has been a speaker and principal investigator of many large-scale national, EU and international research programs (e.g. BMBF, ASAT, Panicnet[13]), DETECT,[14] GEPAD, MentDis65+,[15] ROAMER,[16] World Mental Health Survey, ), WMH,[17] NCS.
Wittchen is author and publisher of books (both in German and in English) on epidemiology and treatment of mental disorders as well as of more than 500 peer-reviewed articles.