Background There is an urgent need for mental health promotion strategies in non-clinical contexts. Mindfulness-based programmes (MBPs) are being widely implemented, but evidence is weak with scattered small trials. High-quality systematic reviews and meta-analyses are lacking. We conducted one to assess the effectiveness of non-clinical MBPs for promoting mental health among community adults compared with no or other interventions.

Methods Thirteen databases were searched using keywords and controlled vocabulary in January 2020 for randomised controlled trials examining in-person, expert-defined non-clinical MBPs (PROSPERO CRD42018105213). Primary outcomes were psychological distress, anxiety, depression and mental wellbeing at 1–6 months after programme completion. Secondary outcomes, meta-regression and sensitivity analyses were pre-defined. Two researchers independently selected, extracted and quality-appraised trials using the Cochrane Risk-of-Bias Tool 2.0. Pairwise random-effects meta-analyses were used. Multiple testing was corrected using p=0.0125 for significance.

Results 10,703 records were identified, 1,372 required full-text screening, and 137 trials were included (29 countries, mean sample size=85). Preliminary main outcome results suggest that compared to no intervention, MBPs improve wellbeing (standardised mean difference (SMD)=0.21 [95%CI 0.07,0.35], p-value=0.003, I2=27%) and may improve distress (SMD -0.40 [95%CI-0.55,-0.24], p-value<0.001, I2=71%) and depression (SMD=-0.72 [95%CI-1.17,-0.27], p-value=0.002, I2=91%), with no clear support for anxiety (SMD=-0.78 [95%CI-1.40,-0.15], p-value=0.015). Against interventions without specific effects on outcomes, MBPs improve depression (SMD=-0.40 [95%CI-0.67, -0.13], p-value=0.003, I2=22%), with no clear support for distress (SMD=-0.25 [95%CI-0.47,-0.03], p-value=0.027) or anxiety (SMD=-0.74 [95%CI-1.39,-0.09], p-value=0.025) (no data for wellbeing). Compared with specific-effect interventions, MBPs did not significantly improve depression (SMD=-0.23 [95%CI-0.59,0.13], p-value=0.21), distress (SMD=0.00 [95%CI-0.15,0.16], p-value=0.96) or wellbeing (SMD=0.00 [95%CI-0.01,0.02], p-value=0.50) (no data for anxiety). Trials’ risk of bias is generally high.

Conclusion Preliminary results suggest that implementing MBPs for non-clinical populations improve wellbeing; other effects depend on contextual factors to be explored further. We found evidence of MBPs’ specific effects on depression only, and no indication of MBPs’ superiority to similar interventions. Low trial quality limits evidence strength.