Despite its high prevalence, help-seeking for depression is low.

To assess the effectiveness and cost-effectiveness of 1-day cognitive–behavioural therapy (CBT) self-confidence workshops in reducing depression. Anxiety, self-esteem, prognostic indicators as well as access were also assessed.

An open randomised controlled trial (RCT) waiting list control design with 12-week follow-up was used (trial registration: ISRCTN26634837). A total of 459 adult participants with depression (Beck Depression Inventory (BDI) scores of 14) self-referred and 382 participants (83%) were followed up.

At follow-up, experimental and control participants differed significantly on the BDI, with an effect size of 0.55. Anxiety and self-esteem also differed. Of those who participated, 25% were GP non-consulters and 32% were from Black and minority ethnic groups. Women benefited more than men on depression scores. The intervention has a 90% chance of being considered cost-effective if a depression-free day is valued at £14.

Self-confidence workshops appear promising in terms of clinical effectiveness, cost-effectiveness and access by difficult-to-engage groups.