Evaluation of a transdiagnostic mental health intervention in German primary care: a parallel-group, two-arm, cluster randomised controlled pilot study

Introduction: Adequate mental health treatment in primary care (PC) is often hindered by structural factors, such as time constraints, and the high comorbidity of mental health conditions. A transdiagnostic approach may help address these challenges, yet evidence on interventions delivered by general practitioners (GPs) remains limited. This pilot study therefore assessed the feasibility, acceptability and potential effectiveness of a GP-led transdiagnostic intervention. Methods: PC practices in Munich (Germany) were randomised (1:1) to an intervention group (IG) or a control group (CG). In the IG, GPs delivered the transdiagnostic intervention focused on psychoeducation, cognitive flexibility and emotion-based avoidance. CG GPs provided improved treatment as usual based on diagnosis-specific clinical guidelines. In both groups, treatment comprised four 20-minute sessions. Feasibility and acceptability (primary outcome) were assessed post-treatment from patients and GPs across key treatment aspects: recruitment, delivery, response, maintenance and unintended consequences. Potential effectiveness (secondary outcome) was observed through patients’ pre-post changes in transdiagnostic factors – beliefs about emotions, cognitive reappraisal, emotion suppression, experiential avoidance and negative affectivity – as early indicators of symptom change. Results: 21 PC practices participated (IG: 11; CG: 10), recruiting 87 patients (mean age: 47 years; 68% female), with 77 (IG: 46; CG: 31) completing treatment. Feasibility and acceptability ratings tended to favour the transdiagnostic intervention. More IG GPs stated a better treatment integration into daily care, greater utility to bridge time until psychotherapy and higher satisfaction with the structure, content as well as perceived patient benefit. Similarly, IG patients rated the treatment structure and content clarity more positively. Relative to CG patients, a trend of greater improvements in transdiagnostic factors over time was observed in IG patients – most pronounced in beliefs about emotions (Emotion Beliefs Questionnaire: -8.87, 95% CI [-15.22, -3.36]), cognitive reappraisal (Emotion Regulation Questionnaire subscale: 6.40, 95% CI [2.84, 10.62]) and experiential avoidance (Brief Experiential Avoidance Questionnaire: -4.90, 95% CI [-9.13, -0.56]). Discussion: The findings support the progression to a fully powered main trial. Future research should optimise recruitment strategies, streamline the intervention and improve outcome monitoring. Trial Registration: The study has been registered with the German Clinical Trials Register: 18 ^th of March 2024, https://drks.de/search/en/trial/DRKS00033386.