Efficacy and mechanisms of internet-delivered MBCT for adjustment disorder during the COVID-19 pandemic: A randomized controlled trial

Background: Adjustment Disorder (AjD) is a common stress-related condition, yet evidence-based interventions remain scarce. Mindfulness-Based Cognitive Therapy (MBCT) targets transdiagnostic mechanisms such as cognitive fusion and low self-compassion, which may be particularly relevant for AjD.Objective: This randomized controlled trial tested the efficacy of a brief, guided, asynchronous internet-delivered MBCT (iMBCT) for AjD during the COVID-19 pandemic, compared with internet-delivered progressive muscle relaxation (iPMR) and a waitlist control (WLC).Methods: Adults meeting ICD-11 criteria for AjD (N = 301) were randomized to iMBCT, iPMR, or WLC for four weeks. Primary outcomes were changes in AjD symptoms (ADNM-20) and remission rates. Secondary outcomes were changes in depression, anxiety, cognitive fusion, experiential avoidance, and self-compassion. Outcomes were assessed at baseline, post-intervention, and one-month follow-up. Mediation analyses tested cognitive defusion and self-compassion as mechanisms. Results: iMBCT produced greater reductions in AjD symptoms than WLC (η² = .17) and higher remission rates. Compared with iPMR, iMBCT yielded larger decreases in depression and anxiety. Cognitive defusion fully mediated iMBCT effects on depression and anxiety. Gains were maintained at follow-up.Conclusions: A brief, minimally guided, asynchronous iMBCT is an effective and scalable intervention for AjD, targeting cognitive and self-regulatory mechanisms. Findings support the use of online mindfulness-based programs for stress-related disorders during large-scale crises.