The Effectiveness of Psychological Interventions for Common Mental Disorders

The primary aim of "the Effectiveness of Psychological Interventions for Common mental disorders" (EPIC) randomized controlled trial is to investigate whether a significantly larger symptom improvement is observed after approximately four months of psychotherapeutic treatment in the Danish primary sector compared to in a waiting list control group. The secondary aim of the study is to identify specific client and therapy characteristics that may predict the effectiveness of the therapy or the symptom development in the waiting list control group. The main hypothesis of the EPIC trial is: 1\) Four and a half months after randomization, we will find a significantly lower level of symptoms on the primary outcome measure (PHQ-ADS) among clients who receive psychotherapy, compared to clients in the waiting list control group. In addition, we hypothesize to find significantly better outcomes in the psychotherapy group on all secondary outcome measures, four and a half months after randomization. Researchers will compare: * Psychotherapy starting within 14 days after the randomization date with * Placement on a waiting list for psychotherapy with treatment starting approximately four and a half months after the randomization date to investigate whether a larger symptom improvement is observed in the group receiving psychotherapy compared to the waiting list control group. Participants will: * Be referred by their general practitioner (GP) for publicly subsidized psychotherapy treatment in the primary care sector in Denmark, based on one of 11 referral reasons. * Complete the baseline questionnaire containing background information, the primary and secondary outcome measures, and predictor questionnaires, and subsequently be randomized to either psychotherapy beginning within two weeks or a waiting list control group. * Receive a brief symptom questionnaire (the PHQ-ADS) every other week after the randomization date via an SMS-based solution provided by REDCap. * Complete the primary and secondary outcome measures approximately four and a half, eight and a half, and 16 and a half months after the randomization date.