There is currently a lack of empirical studies investigating whether specific personality traits moderate the effects of mindfulness-based interventions (MBIs) on distinct adolescent mental health outcomes. This study examined how personality traits from a five-factor model (agreeableness, conscientiousness, emotional stability, extraversion, and openness to experience) moderate the effects of an MBI in schools on adolescents’ depression, socio-emotional functioning, and resilience.

A total of 2773 Finnish students aged 12–15 years participated in a cluster randomized controlled trial with three arms: a 9-week MBI (the.b program), a 9-week active control condition (a relaxation program), and an inactive control condition (the routine school curriculum). Personality traits were assessed before the MBI (T0). Mental health was evaluated before (T0) and after (T9) the intervention, as well as at a 26-week follow-up (T26), using scores for depressive symptoms, socio-emotional functioning difficulties, and resilience.

When compared with both control groups, personality traits did not moderate the effects of the MBI on resilience or socio-emotional functioning. Most of the moderation analyses were also nonsignificant on depressive symptoms. Only, at the 26-week follow-up, the analyses indicated a small moderating effect on the change in depressive symptoms between the MBI and active control groups (β = 0.31, 95% CI [0.002 to 0.63], p = 0.048), with adolescents in the MBI group scoring low in extraversion showing the greatest improvement. The results did not differ by gender.

These preliminary findings suggest that the moderation effects were largely nonsignificant across personality traits and mental health outcomes, with only a small, exploratory interaction for extraversion observed at the follow-up. Further research is warranted to replicate these findings and to investigate their generalizability across diverse populations.