Esteller Collado, GabrielPrieto Vila, MaiderCarpallo González, MaríaAntuña Camblor, CeliaRuiz Rodríguez, PalomaGonzález Blanch, CésarMoriana, Juan AntonioCano Vindel, AntonioMuñoz Navarro, Roger2025-11-152025-11-152025Esteller-Collado, G., Prieto-Vila, M., Carpallo-González, M., Antuña-Camblor, C., Ruíz-Rodríguez, P., González-Blanch, C., Moriana, J. A., Cano-Vindel, A., & Muñoz-Navarro, R. (2025). Mechanisms of change in long-term transdiagnostic cognitive behavioural therapy: The sequential effect of rumination and worry on symptoms and quality of life. Cognitive Behaviour Therapy, 1-15. https://doi.org/10.1080/16506073.2025.25731991650-60731651-2316https://hdl.handle.net/11268/16474Anxiety and depressive disorders are the most prevalent disorders worldwide and significantly impair quality of life (QoL). Transdiagnostic cognitive behavioural therapy (TD-CBT) is effective in treating these disorders and improving QoL, but its long-term mechanisms of change are poorly understood. Rumination and worry are key processes addressed by TD-CBT. In this study, we analysed the sequential effect of TD-CBT on post- treatment rumination and worry, anxiety/depression symptoms at 6-months and psychological and physical QoL at 12-months. We use data from PsicAP, a randomised clinical trial in the Primary Care (PC) setting, with 1061 participants randomised to TAU (treatment as usual) or TD-CBT+TAU. Path analyses using SEM were employed to test serial mediation models. Analyses indicated that TD-CBT exerts its long-term beneficial effects on QoL through a cascade of effects, whereby first the maladaptive cognitive processes of rumination and worry are reduced (post-treatment), then anxiety and depressive symptoms (6-months) and finally QoL is improved (12-months). This study provides longitudinal evidence on the mechanisms of change of TD-CBT in patients with anxiety and depression. It also highlights the importance of targeting transdiagnostic interventions towards early modification of negative repetitive thought processes as a critical pathway to long-term symptomatic and functional recovery.engAttribution-NonCommercial-NoDerivatives 4.0 Internationalhttp://creativecommons.org/licenses/by-nc-nd/4.0/journal article10.1080/16506073.2025.2573199open accessCiencias médicasPsicología clínicaPsicología socialGoal 3: Ensure healthy lives and promote well-being for all at all agesGoal 4: Quality educationGoal 5: Achieve gender equality and empower all women and girls