Do psychological interventions in childhood and adolescence prevent later mental illness? A commentary on Vassard et al. (2026)

Early intervention in youth mental health has long been assumed to confer long‐term benefits, altering developmental trajectories and reducing risk of later mental disorders. The 3‐year follow‐up of the Mind My Mind (MMM) trial challenges these assumptions. The MMM transdiagnostic cognitive behavioural therapy (CBT) intervention led to clinically meaningful improvements at the end of treatment and at short‐term follow‐up. Its superiority over management as usual, however, was not sustained at 3 years, and rates of subsequent specialist psychiatric diagnosis did not differ between the MMM and control groups. These findings highlight that effective psychological intervention in youth does not necessarily alter longer‐term mental health trajectories. Prevention science in youth mental health must move beyond equating early treatment with durable change and instead clarify the mechanisms and targets required to alter developmental trajectories toward serious mental illness.