Abstract
<title>Abstract</title> <p>Background Non-suicidal self-injury (NSSI) represents a severe mental health problem among adolescents and young adults, often associated with numerous psychiatric comorbidities. Although several mechanisms of NSSI have been proposed, childhood adversity is one of the strongest risk factors for NSSI. However, evidence regarding its influence on psychotherapeutic treatment response remains mixed. Moreover, specific interventions for the treatment of NSSI have remained limited. To address this gap, we developed the Transitional Age Youth Self-Harm (TaySH). The present study aimed to evaluate the effectiveness of the TaySH Program in an outpatient clinical sample using repeated pre–post and follow-up assessments (baseline, post-treatment, and six months after the beginning of the intervention) to reduce NSSI and associated clinical symptoms and analyze the role of childhood adversity in treatment response and the maintenance of therapeutic gains over time. Methods A prospective quasi-experimental pre–post design with repeated measures was used. 57 individuals aged 14–25 with a history of NSSI were recruited. 45 participants completed the 12-session TaySH program and pre–post assessments; 21 completed a 3-month follow-up. Changes were analyzed using repeated-measures General Linear Models (GLMs), including Childhood Trauma Questionnaire (CTQ) total, abuse, and neglect scores as covariates. Results Significant improvements were observed across all domains after the intervention, with large effects for reductions in NSSI (η²=0.473), suicidal risk (η²=0.674), emotion dysregulation (η²=0.648), depressive symptoms (η²= 0.664), anxiety (η²=0.483), and functional impairment (η²=0.517). Marked reductions were also found in borderline personality features, with large effect sizes across all measures (η² up to 0.716). Improvements were maintained at follow-up for suicidal risk (η²=0.849), emotion dysregulation (η²=0.738), depression (η²=0.754) and borderline personality features (η² up to 0.912). Despite marked baseline differences, suicidal risk levels at post-treatment and follow-up were comparable between participants with higher and lower trauma exposure. Conclusions The TaySH Program appears to be a feasible and effective intervention for young individuals with NSSI, promoting substantial and sustained improvements across multiple clinical and functional domains. These findings suggest that childhood adversity, particularly abuse, may shape the longitudinal course of suicidal risk without diminishing the overall effectiveness of the intervention.</p>