Background: Guided Imagery Psychotherapy (GIP) is an established therapeutic method in several countries. In addition to applying the established principles of psychodynamic psychotherapy, the GIP practitioner also regularly conducts sessions in which the patient is asked to imagine their own version of a pre-determined motif (e.g., a mountain or a house) and immediately describe it to the therapist. The patient is meant to allow the image to spontaneously develop further, and to experience its sensual properties while remaining in dialogue with the therapist. The therapist aims to guide and deepen the imagery process by asking questions about the patient's bodily and emotional experiencing and sometimes also by suggesting certain courses of action within the patient's imagined scenery. The patient is instructed to draw his imagery in between sessions. During non-imagery sessions, therapist and patient jointly work to understand the patient's spontaneous imagery within a psychodynamic framework and relate it back to the patient's psychological difficulties. GIP is especially aimed at treating patients with depression, anxiety as well as psychosomatic conditions.

Design and aims: This is a two-arm randomized non-inferiority trial. In addition, the study is used to explore and test possible differential indications of GIP. Manualized GIP for emotional disorders (GIP-EMO) is tested against the manualized psychodynamic therapy according to the unified psychodynamic protocol for emotional disorders (UPP-EMO) as an active comparator. The aim is to test two independent hypotheses: 1) GIP-EMO is non-inferior (NI margin: 5 points in the PHQ-ADS (d = 0.46) requiring N = 152, α = 0.025, 1-ß = 0.80) to UPP-EMO with regard to anxiety and depression severity 12 months after the beginning of treatment. 2) There is a subgroup of patients for whom GIP-EMO is particularly effective. The investigatorshave developed a therapist-questionnaire (Suitability Questionnaire for Guided Imagery Psychotherapy) to assess potential GIP suitability criteria in the patients of the sample. The investigators expect that GIP-EMO is more effective for patients meeting the GIP suitability criteria than for patients who do not meet these criteria. Furthermore, it will be tested whether GIP-EMO is more effective than UPP-EMO for patients who meet the GIP suitability criteria.

Interventions, patient recruitment, and measurements: The interventions in both treatment conditions are regarded as forms of psychodynamic psychotherapy by German legal standards. They are therefore equally eligibly for financial coverage by statutory health insurances. Currently, up to 24 sessions of psychodynamic psychotherapy require only a formal notification to the health insurance. After that, therapist and patient need to file an application for long-term treatment, entailing up to 100 sessions in total. Sessions are in the face-to-face setting and can be weekly, biweekly, or twice a week. The study design does not impose any further requirement regarding treatment length or frequency of sessions. Patients are recruited trough the participating therapists in their private practices. Baseline assessment and eligibility check takes place prior to randomization, that is: after the initial telephone contact between patient and therapist. The assessment includes online questionnaires for the patient and the therapist as well as a SCID interview for the patient. The interviews are conducted via telephone by trained research assistants. For the duration of the treatment, patients complete monthly online questionnaires. After the end of treatment, they complete the same questionnaire every three months. All therapy sessions will be audio-recorded so that treatment fidelity can be assessed by independent raters (Comparative Psychotherapy Process Scale; Process Scale for Imagery- and Trance-Based Psychodynamic Therapies). The primary outcome assessment takes place 12 months after the beginning of treatment and is thus independent of length of treatment or treatment condition. Further follow-up assessments are conducted until 48 months after the beginning of treatment.

Non-inferiority specifications and sample size determination: the investigators determined the margins of non-inferiority (NI) based on the recommendation that the threshold for NI be set to the minimum clinically important difference (MCID) of the primary outcome scale. The MCID was determined as follows: in validation studies for the PHQ-ADS, the authors recommend using either a 1-SEM (standard error of measurement) change (3 to 4 points in the PHQ-ADS) or a 2-SEM change (6 to 8 points in the PHQ-ADS) as MCID. As a compromise, the investigators chose 5 points in the PHQ-ADS as MCID for this study, which is equivalent to an effect size of d = 0.46 given the mean SD of 10.87 found across the three samples of the PHQ-ADS validation study. As a result, the investigators accept the non-inferiority of GIP-EMO to UPP-EMO if the upper limit of the one-sided 0.975 CI of the adjusted mean difference between treatments in favor of UPP-EMO is 5 or below. To test the non-inferiority hypothesis at a one-sided 2.5% significance level with a power of 80%, n = 76 patients are needed per treatment condition. The final sample size includes an oversampling to compensate for an expected loss of 15% to the 12-month follow-up.

Statistical analyses: the investigators shall use intention to treat (ITT) analysis (including all patients who were randomized), using linear-mixed effect models to appropriately deal with repeated measures, nested data, and missing values. Duration and total number of sessions will be included as covariates and therapists as a random coefficient. The investigators shall also use multiple imputations by chained equations to account for data missing at random in the primary outcome. Additional modified ITT analyses (including only patients who started treatment) and per protocol analyses (including only patients who completed treatment) will be conducted to assess the robustness of the results.