Cognitive behavioural therapy (CBT) and interpersonal psychotherapy (IPT) are both efficacious treatments for depression, but it is less clear how both compare on outcome domains other than depression and in the longer term. Moreover, it is unclear which of these two psychotherapies works better for whom. This article describes the protocol for a systematic review and individual participant data (IPD) meta-analysis that aims to compare the efficacy of CBT and IPT for adults with depression on a range of outcomes in both the short and long term, and to explore moderators of the treatment effect. This study can enhance our understanding of treatments for depression and inform treatment personalisation.

Systematic literature searches will be conducted in PubMed, PsycINFO, EMBASE and the Cochrane Library from inception to 1 January 2026, to identify randomised clinical trials (RCTs) comparing CBT and IPT for adult depression. Researchers of eligible studies will be invited to contribute their participant-level data. One-stage IPD meta-analyses will be conducted with mixed-effects models to examine (a) treatment efficacy on all outcome measures that are assessed at post-treatment or follow-up in at least two studies, and (b) various baseline participant characteristics as potential moderators of depressive symptom level at treatment completion.

Ethical approval is not required for this study since it will be based on anonymised data from RCTs that have already been completed. The findings of the present study will be disseminated through a peer-reviewed journal or conference presentation.