Depressive Symptoms Mediate the Association Between Family Functioning and Non-Suicidal Self-Injury in Adolescent Psychiatric Patients: A Cross-Sectional Study.

BACKGROUND: Non-suicidal self-injury (NSSI) is highly prevalent among adolescent psychiatric patients, yet the pathways linking family functioning to NSSI have not been fully elucidated. This study aimed to investigate whether depressive symptoms function as a mediator in the association between family functioning and NSSI among adolescent psychiatric inpatients. METHODS: A cross-sectional study was conducted among 180 adolescent patients admitted to a psychiatric department between June 2023 and June 2025. Family functioning, depressive symptoms, and NSSI-related frequency (encompassing both NSSI ideation and actual NSSI behaviours) were assessed using validated Chinese versions of the Family Adaptability and Cohesion Evaluation Scale II, Patient Health Questionnaire-9 (PHQ-9), and Ottawa Self-Injury Inventory. To avoid measurement overlap between the mediator and outcome, the PHQ-8 total score (PHQ-9 excluding the self-harm/suicide item) was employed as the mediator in the primary analysis. Mediation analysis was performed using the PROCESS macro with bootstrap methods, controlling for demographic and clinical covariates including age, sex, only-child status, parental marital status, family monthly income, duration of illness, history of suicide attempts, and primary diagnosis. RESULTS: NSSI was identified in 60.56% of participants. Family functioning was negatively correlated with depressive symptoms (r = -0.463, p < 0.001) and NSSI-related frequency score (r = -0.387, p < 0.001). Depressive symptoms partially mediated the association between family functioning and NSSI-related frequency (indirect effect = -0.058, 95% CI [-0.092, -0.029], accounting for 34.52% of the total effect. Sensitivity analyses including comparison with the original PHQ-9 as mediator (proportion mediated = 40.48%) and a most conservative model utilising only NSSI behavioural items as the outcome (proportion mediated = 35.16%) confirmed the robustness of these findings. CONCLUSIONS: Among adolescents with mental disorders, depressive symptoms may partially mediate the negative association between family functioning and nonsuicidal self-injury. Interventions may benefit from integrating family-based approaches with depression-targeted therapies to address NSSI in this vulnerable population.