Cognitive and behavioural skills to prevent major depression among adults with subthreshold depression: 50-week follow-up analysis of smartphone CBT randomised trials (RESiLIENT trial)

BACKGROUND: Major depression is a common and disabling disorder, and individuals with subthreshold depression represent a key at-risk group. We previously demonstrated that specific cognitive behavioural therapy (CBT) skills training delivered via a smartphone app (behavioural activation, cognitive restructuring, problem solving, assertion training and behavioural therapy for insomnia) improved depressive symptoms for up to 26 weeks. AIMS: To evaluate the long-term effects (up to 50 weeks) of CBT skills and their combinations for preventing major depressive episodes and reducing the total burden of depression (TBD). METHOD: Participants were adults from the general population with subthreshold depression. A master protocol trial with four 2 × 2 factorial trials was used to randomise 3280 participants to one of nine intervention arms or a self-check control group. The primary outcome was time to onset of major depression by week 50. RESULTS: Hazard ratios for the interventions ranged from 0.52 (95% CI: 0.29-0.94) to 0.63 (95% CI: 0.36-1.10), with behavioural activation + assertion training showing the greatest preventive effect (number needed to treat: 23.3 (95% CI: 12.2 to 250)), followed by behavioural therapy for insomnia, behavioural activation + behavioural therapy for insomnia and cognitive restructuring. All interventions reduced TBD scores compared with control, with behavioural activation + cognitive restructuring exhibiting the largest reduction. Effect sizes at week 50 ranged from -0.34 to -0.07 and behavioural activation + cognitive restructuring was the most effective. No serious adverse events were reported. CONCLUSIONS: The current findings indicated that specific CBT skills - particularly behavioural activation +assertion training , behavioural activation + cognitive restructuring and behavioural therapy for insomnia - effectively prevented the onset of depression and reduced the TBD at 50 weeks. Given its brevity, portability, accessibility and scalability, smartphone-based CBT is promising as a preventive intervention.