King's College London

Brief, evidence-based interventions for adolescent depression are urgently required, 25 particularly for school-settings. Cognitive mechanisms research suggests dysfunctional 26 mental imagery and overgeneral memory could be promising targets to improve mood. This 27 feasibility randomised controlled trial with parallel symptomatic groups (n=56) compared a 28 novel imagery-based cognitive behavioural intervention (ICBI) to non-directive supportive 29 therapy (NDST) in school settings. Blind assessments (of clinical symptoms and cognitive 30 mechanisms) took place pre-intervention, post-intervention and follow-up three months later. 31 The trial aimed to evaluate the feasibility and acceptability of the methodology and 32 interventions, and estimate the likely range of effects of the intervention on self-reported 33 depression. The pre-defined criteria for proceeding to a definitive RCT were met: full 34 recruitment occurred within eleven months; retention was 89%; ICBI acceptability was above 35 satisfactory; and no harm was indicated. Intention-to-treat analysis found large effects in 36 favour of ICBI (relative to NDST) at post-intervention in reducing depressive symptoms (d=-37 1.34, 95% CI [-1.87, -0.80]) and improving memory specificity (d=0.79 [0.35, 1.23]), a key 38 cognitive target. The findings suggest that ICBI may not only improve mood but also 39 strengthen abilities associated with imagining and planning the future, critical skills at this 40 life stage.