Objectives: Depression, a common mental health problem, is projected to be the second leading cause of disability for adults by year 2020. Mindfulness-based interventions (MFIs) have been integrated into therapeutic work on depression, but limited systematic reviews reported their efficacy on heterogeneous groups of mental disorders. This meta-analysis aimed to examine the efficacy of the MFIs on depressive symptoms in people with various mental disorders.

Design: A meta-analysis of experimental and quasi-experimental studies was undertaken.

Data sources: Multiple search strategies were undertaken to identify published and unpublished studies conducted between 1995 and 2011. Electronic databases used were Scopus, CINAHL, PubMed, ScienceDirect, PsyINFO, Dissertation Abstract International, Web of Science Index, Controlled-trial.com, and clinicaltrials.gov.

Review methods: Data were extracted and appraised by two reviewers. For each study, the Quality Rating Index (QRI) and Code Sheet for Randomized Controlled Trials (CS-RCT) were used to assess methodological quality and extract relevant data respectively. Data were analysed and synthesized using PASW statistic 17.0 and Comprehensive Meta Analyses Software 2.0.

Results: Thirty-nine studies conducted in ten countries were included and 105 effect sizes were calculated. Most studies utilised single group pretest-posttest quasi-experimental design, convenience sampling, and self-reported questionnaires. Between-group comparisons indicated that MFIs are superior to standard care in reducing depressive symptoms and preventing relapse with effect sizes ranging from 0.11 to 1.65. Exposure-based cognitive therapy (d=2.09) appeared to be the most efficacious intervention, followed by mindfulness-based stress reduction programme (d=1.92), acceptance-based behaviour therapy (d=1.33), and stress less with mindfulness (d=1.31). Effect sizes were significantly associated with the length of intervention sessions but not related to methodological quality of studies.

Conclusion: The mindfulness-based interventions are efficacious for alleviating depressive symptoms in adults with mental disorders. The interventions could be used in conjunction with other treatments in clinical settings.