Introduction: Psychotherapy has long been acknowledged for its positive effects in the treatment of several psychological problems and mental illnesses, and many people continue to enter psychotherapeutic treatment. In pharmacological research, demands for evidence and knowledge about side effects is a crucial part of the licensing process. Since pharmacological treatments to mental problems have the potential to do harm, psychotherapy interventions might pose a similar risk. Although theoretical literature exists on this issue, the amount of available empirical research is pointed out as rather limited. This study therefore sought to examine possible adverse effects of psychotherapy through the research question: What is the evidence of adverse effects of psychotherapy among adults? Method: To examine adverse effects of psychotherapy a scoping review was conducted following the guidelines of PRISMA-SCR. A systematic search of literature was conducted in two databases supplemented by an additional control search of the reference lists of the included studies. The screening process was performed by both authors on the basis of a number of in- and exclusion criteria. Formulation of the synthesis of results were based on data extraction in relation to descriptive information, demographic characteristics and study results. Results: A total number of eight studies were included in the review. All of the studies varied substantially from each other displaying great variation in study design, aim, assessment, use of checklists and questionnaires, participants and more. Concerning adverse effects, an overall high estimate of frequency was found indicating that negative effects can occur in psychotherapy. Many different effects were identified and merged into four thematic categories; reactions to treatment, symptomatic changes, emotionally alterations and external impact. The concrete effects included in these categories are multifaceted in both type and content. Also, different risk factors related to the treatment, therapist and client were found. Discussion: By comparing the empirical indications to theoretical assumptions a great overlap was found with only a few theoretical shortcomings. Especially in regard to risk factors related to the client the theoretical background seems inadequate. Since adverse effects were found across different therapeutic orientations within the study interventions, the empirical assumptions indicate that negative effects are not specific to any form of treatment and should be seen in light of psychotherapeutic nonspecific factors. However, some negative effects can be related to specific procedures within interventions and thus indicate on a concrete level that some effects are related to specific factors. The consistency between the empirical indications and the theoretical assumptions supports the possibility of defining knowledge about negative effects as evidence-based. Although the understanding of evidence might differ from classical understandings, evidence can occur based on phenomenological results. Since only eight studies with different results contributed to the findings the necessity for more comprehensive research arises to establish a more reliable and valid foundation of evidence. For psychological practices the findings from this review identifies the need of raising awareness in order to create more realistic client expectations and to remove pressure from the therapist and make it possible to recognize the impact of negative effects and possibly work with reactions in relation to adverse effects in the therapeutic setting. Also, a more reasonable and fairer frame of reference between pharmacological and psychological treatments is guaranteed, since assessment of side-effects is required in examinations of effects in medical practices. Conclusion: Ending the review we found that psychotherapy is not harmless in the treatment of adults in mental distress. The review resulted in phenomenological evidence for a wide range of negative effects which overlap with the theoretical background to a wide extent. Thus, there is scientific backing for working with negative effects in psychology. However, the result is based on a limited amount of studies with idiosyncratic results which indicate a need for more empirical research on this topic.