Negative or adverse effects of psychological treatments are increasingly a focus of psychotherapy research. Yet, we still know little about the prevalence of these effects.

Starting from a representative national sample, the prevalence of negative effects and malpractice was determined in a subsample of individuals reporting psychotherapy currently or during the past 6 years.

Out of an initial representative sample of 5562 individuals, 244 were determined to have had psychotherapy within the past 6 years. Besides answering questions related to treatment, its effects and the therapists, patients filled out the Negative Effects Questionnaire, items of the Inventory of Negative Effects of Psychotherapy reflecting malpractice and the Helping Alliance Questionnaire, and rated psychotherapeutic changes in different areas.

Rates of positive changes related to therapy varied between 26.6% (relationship to parents) and 67.7% (improvement in depressed mood). Deteriorations were most commonly related to physical well-being (13.1%), ability to work (13.1%) and vitality (11.1%). Although patients generally reported a positive helping alliance, many of them reported high rates of negative effects (though not always linked to treatment). This was especially true of the experience of unpleasant memories (57.8%), unpleasant feelings (30.3%) and a lack of understanding of the treatment/therapist (19.3/18.4%). Indicators of malpractice were less common, with the exception that 16.8% felt violated by statements of their therapist.

This study helps to better estimate aspects of negative effects in psychotherapy ranging from deteriorations, specific effects and issues of malpractice that should be replicated and specified in future studies.