Background: Nonsuicidal self-injury (NSSI) is a serious and prevalent problem among the adult population. Despite its significant issue in clinical settings, there is a lack of effective, evidence-based, and affordable treatment options for NSSI. Objectives: This study aimed to compare the efficacies of transdiagnostic therapy based on the Research Domain Criteria framework (TTB-RDoC) with treatment as usual (TAU) and transcranial direct current stimulation (tDCS) in the treatment of adult NSSI. Methods: A total of 68 males aged 18-30 years diagnosed with NSSI participated in this randomized controlled trial (RCT). Participants were randomly assigned to 3 groups: TTB-RDoC (n = 24), TAU (n = 22), and tDCS (n = 22). Nonsuicidal self-injury and transdiagnostic symptoms were assessed at baseline, post-treatment, and during a 12-month follow-up. Results: Both TAU and TTB-RDoC treatments resulted in significantly lower ratings across all measures compared to tDCS at post-treatment (all P values < 0.001). TAU and TTB-RDoC showed significantly greater reductions in NSSI (P = 0.001 [post-treatment]; P = 0.001 [follow-up]) compared to tDCS. Conclusions: TTB-RDoC treatment may be an effective strategy to improve long-term treatment outcomes in adult NSSI.

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