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.

FUNDING: Danish Health Insurance Foundation; the Research Council of Psychiatry, Region of Southern Denmark; the Research Council of Psychiatry, Capital Region of Denmark; and the Strategic Research Grant from Health Sciences, Capital Region of Denmark.