Long-term effectiveness and cost-effectiveness of cognitive behavioural therapy as an adjunct to pharmacotherapy for treatment-resistant depression in primary care: follow-up of the CoBalT randomised controlled trial

Summary Background Cognitive behavioural therapy (CBT) is an effective treatment for people whose depression has not responded to antidepressants. However, the long-term outcome is unknown. In a long-term follow-up of the CoBalT trial, we examined the clinical and cost-effectiveness of cognitive behavioural therapy as an adjunct to usual care that included medication over 3–5 years in primary care patients with treatment-resistant depression. Methods CoBalT was a randomised controlled trial done across 73 general practices in three UK centres. CoBalT recruited patients aged 18–75 years who had adhered to antidepressants for at least 6 weeks and had substantial depressive symptoms (Beck Depression Inventory [BDI-II] score ≥14 and met ICD-10 depression criteria). Participants were randomly assigned using a computer generated code, to receive either usual care or CBT in addition to usual care. Patients eligible for the long-term follow-up were those who had not withdrawn by the 12 month follow-up and had given their consent to being re-contacted. Those willing to participate were asked to return the postal questionnaire to the research team. One postal reminder was sent and non-responders were contacted by telephone to complete a brief questionnaire. Data were also collected from general practitioner notes. Follow-up took place at a variable interval after randomisation (3–5 years). The primary outcome was self-report of depressive symptoms assessed by BDI-II score (range 0–63), analysed by intention to treat. Cost-utility analysis compared health and social care costs with quality-adjusted life-years (QALYs). This study is registered with isrctn.com , number ISRCTN38231611. Findings Between Nov 4, 2008, and Sept 30, 2010, 469 eligible participants were randomised into the CoBalT study. Of these, 248 individuals completed a long-term follow-up questionnaire and provided data for the primary outcome (136 in the intervention group vs 112 in the usual care group). At follow-up (median 45·5 months [IQR 42·5–51·1]), the intervention group had a mean BDI-II score of 19·2 (SD 13·8) compared with a mean BDI-II score of 23·4 (SD 13·2) for the usual care group (repeated measures analysis over the 46 months: difference in means −4·7 [95% CI −6·4 to −3·0, p