Cognitive behaviour therapy (CBT) is a much-debated subject in terms of its efficacy and status as the ‘treatment of choice’ for depression and anxiety. This article critically analyses the claimed merits of this therapy over others, and evaluates its efficacy as a standalone ‘combined therapy’, by examining dismantling, additive, comparative and component studies. The article examines behavioural activation in particular, as the contested active ingredient in the cognitive behavioural model, and the application of this and CBT in the context of evidence-based, person-centred and holistic mental health nursing practice.