BACKGROUND: Individuals with depression often do not respond to medication or psychotherapy. Radically open dialectical behaviour therapy (RO DBT) is a new treatment targeting overcontrolled personality, common in refractory depression.

AIMS: To compare RO DBT plus treatment as usual (TAU) for refractory depression with TAU alone (trial registration: ISRCTN 85784627).

METHOD: RO DBT comprised 29 therapy sessions and 27 skills classes over 6 months. Our completed randomised trial evaluated RO DBT for refractory depression over 18 months in three British secondary care centres. Of 250 adult participants, we randomised 162 (65%) to RO DBT. The primary outcome was the Hamilton Rating Scale for Depression (HRSD), assessed masked and analysed by treatment allocated.

RESULTS: After 7 months, immediately following therapy, RO DBT had significantly reduced depressive symptoms by 5.40 points on the HRSD relative to TAU (95% CI 0.94-9.85). After 12 months (primary end-point), the difference of 2.15 points on the HRSD in favour of RO DBT was not significant (95% CI -2.28 to 6.59); nor was that of 1.69 points on the HRSD at 18 months (95% CI -2.84 to 6.22). Throughout RO DBT participants reported significantly better psychological flexibility and emotional coping than controls. However, they reported eight possible serious adverse reactions compared with none in the control group.

CONCLUSIONS: The RO DBT group reported significantly lower HRSD scores than the control group after 7 months, but not thereafter. The imbalance in serious adverse reactions was probably because of the controls' limited opportunities to report these.