Short-term and long-term effects of psychosocial therapy for people after deliberate self-harm: a register-based, nationwide multicentre study using propensity score matching

Background Although deliberate self-harm is a strong predictor of suicide, evidence for effective interventions is missing. The aim of this study was to examine whether psychosocial therapy after self-harm was linked to lower risks of repeated self-harm, suicide, and general mortality. Methods In this matched cohort study all people who, after deliberate self-harm, received a psychosocial therapy intervention at suicide prevention clinics in Denmark during 1992-2010 were compared with people who did not receive the psychosocial therapy intervention after deliberate self-harm. We applied propensity score matching with a 1: 3 ratio and 31 matching factors, and calculated odds ratios for 1, 5, 10, and 20 years of follow-up. The primary endpoints were repeated self-harm, death by suicide, and death by any cause. Findings 5678 recipients of psychosocial therapy (followed up for 42.828 person-years) were matched with 17 034 individuals with no psychosocial therapy in a 1: 8 ratio. During 20 year follow-up, 937 (16.5%) recipients of psychosocial therapy repeated the act of self-harm, and 391 (6.9%) died, 93 (16%) by suicide. The psychosocial therapy intervention was linked to lower risks of self-harm than was no psychosocial therapy (odds ratio [OR] 0.73, 95% CI 0.65-0.82) and death by any cause (0.62, 0.47-0.82) within a year. Long-term effects were identified for repeated self-harm (0.84, 0.77-0.91; absolute risk reduction [ARR] 2.6%, 1.5-3.7; numbers needed to treat [NNT] 39, 95% CI 27-69), deaths by suicide (OR 0.75, 0.60-0.94; ARR 0.5%, 0.1-0.9; NNT 188, 108-725), and death by any cause (OR 0.69, 0.62-0.78; ARR 2.7%, 2.0-3.5; NNT 37, 29-52), implying that 145 self-harm episodes and 153 deaths, including 30 deaths by suicide, were prevented. Interpretation Our findings show a lower risk of repeated deliberate self-harm and general mortality in recipients of psychosocial therapy after short-term and long-term follow-up, and a protective effect for suicide after long-term follow-up, which favour the use of psychosocial therapy interventions after deliberate self-harm.