Effectiveness and cost-effectiveness of universal school-based mindfulness training compared with normal school provision in reducing risk of mental health problems and promoting well-being in adolescence: the MYRIAD cluster randomised controlled trial

85 schools consented and were randomised 1:1 (43 teaching-as-usual with 4,232 students, 42 mindfulness with 4,144); 84 schools and 8,376 participants analysed

United Kingdom; students aged 11-14 (mean 12.2), broadly population-representative.

The largest school mental-health randomised trial ever run, and the definitive test of school mindfulness. Parallel-group cluster RCT stratified by school size, quality, type, deprivation and region, registered as ISRCTN86619085 with a protocol published in advance, intention-to-treat with multiple imputation, retention around 87%. The control is teaching as usual, which in English schools IS standard social-emotional teaching - so this is effectively an active comparison. Every co-primary outcome is self-report, which is the design's main weakness and the field's own choice of yardstick. Competing interests are declared - the trial's director and a co-author are current and former directors of the Oxford Mindfulness Centre and receive royalties on mindfulness books, which makes a null from this team unusually informative.

All three co-primary outcomes at one year are indistinguishable from zero. Risk for depression standardized mean difference 0.005 (95% CI -0.05 to 0.06); social-emotional-behavioural functioning 0.02 (-0.02 to 0.07); wellbeing 0.02 (-0.03 to 0.07). The authors state that important effects can be ruled out on the basis of the confidence intervals. Five of 28 secondary outcomes differed between arms and ALL FIVE FAVOURED THE CONTROL - higher self-reported hyperactivity and inattention in the intervention arm at post-intervention and at one year (adjusted difference 0.2, 0.04 to 0.3, p = 0.01), higher panic and obsessive-compulsive scores post-intervention, LOWER mindfulness skills post-intervention, and higher teacher-reported emotional symptoms at one year. Self-harm and suicidal ideation were null.

Low. School-level cluster randomisation.

A definitive failure to reproduce the prior small-trial mindfulness literature. Its own consortium's mechanism trial (Dunning et al. 2022) found no effect on affective executive control either, and their updated meta-analysis shows the youth mindfulness effect on executive function is 0.04 against active controls.