Mindfulness-based interventions are widely used, yet concerns about potential negative effects—particularly those related to mindfulness meditation practice—have gained increasing attention. Individuals with difficult-to-treat depression (DTD) represent a population of particular relevance due to heightened vulnerability, but comparative evidence on clinically relevant negative outcomes of mindfulness-based cognitive therapy (MBCT) versus established alternative psychotherapies in this group is lacking. This protocol describes a systematic review and individual participant data (IPD) network meta-analysis to assess and compare the incidence of clinically relevant negative outcomes associated with MBCT and the cognitive behavioural analysis system of psychotherapy (CBASP), an established individual psychotherapy for DTD.

Randomised controlled trials of MBCT and CBASP for adults with DTD were identified through systematic searches of major databases. Eligible studies must compare MBCT or CBASP (alone or with treatment as usual) to each other or to control groups. The primary outcome is clinically significant deterioration, defined as a ≥6-point increase on the Patient Health Questionnaire-9 or equivalent. Secondary outcomes are suicidality and treatment dropout. IPD will be requested from trial investigators; aggregate data will be used when IPD is unavailable. One-stage random-effects IPD network meta-analyses will be conducted to integrate direct and indirect evidence and to examine participant-level moderators of deterioration. Adverse events reported in the included trials will be summarised descriptively at the study level.

No local ethical review was required following consultation with the Swedish Ethical Review Authority. Primary trial investigators obtained local ethical approval and will share pseudonymised IPD. Findings will inform clinical decision-making and guideline development by strengthening the evidence base on potential negative effects of MBCT and CBASP in adults with DTD, including identification of subgroups at increased risk. Results will be disseminated through peer-reviewed publication and accessible summaries for relevant stakeholders.

CRD42022332039

About 30% of depressed patients suffer from a protracted course in which the disorder continues to cause significant burden despite treatment efforts. While originally developed for relapse prevention, mindfulness-based cognitive therapy (MBCT) has increasingly been investigated in depressed patients with such ‘difficult-to-treat’ courses. This is a protocol for an individual participant data (IPD) meta-analysis aiming to determine efficacy and potential moderators of MBCT treatment effects in this group based on evidence from randomised controlled trials.

Systematic searches in PubMed, Web of Science, Scopus, PsycINFO, EMBASE and the Cochrane Controlled Trials Register for randomised controlled trials were completed on 17 June 2024. Authors of identified studies have contributed IPD, and data extractions have been completed. An update search will be conducted immediately before the start of data analyses. We will investigate the following outcomes: (a) self-reported and observer-reported severity of depression symptomatology, (b) remission and (c) clinically meaningful improvement and deterioration. One-stage and two-stage IPD-MA will be conducted with one-stage models using the observed IPD from all studies simultaneously as the primary approach. One-stage IPD models will include stratified study intercepts and error terms as well as random effects to capture between-study heterogeneity. Moderator analyses will test treatment-covariate interactions for both individual patient-level and study-level characteristics.

The results will inform understanding of the use of MBCT in patients with current ‘difficult-to-treat’ depression and will contribute to arguments in favour of or against implementing MBCT as a treatment for this group. They will be published in a peer-reviewed journal and made available to stakeholders in accessible formats. No local ethical review was necessary following consultation with the Ethics and Governance Board of the University of Surrey. Guidance on patient data storage and management will be adhered to throughout.

CRD42022332039.