The goal of this randomized, parallel-controlled clinical trial is to investigate multi-dimensional biomarkers (blood, brain imaging, clinical information, and symptom assessment) in adolescents with Non-Suicidal Self-Injury (NSSI) and to evaluate the therapeutic and prognostic effects of a novel digital psychological intervention plus treatment as usual (TAU) compared to TAU alone in this population.

The main question[s] it aims to answer [is/are]:

What are the distinct biomarker profiles (e.g., inflammatory, endocrine, neuroimaging) associated with adolescent NSSI? Does the novel digital psychological intervention (based on CBT and DBT) combined with TAU lead to a higher clinical response rate (≥25% reduction in NSSI scale score from baseline) at 8 and 16 weeks compared to TAU alone?

If there is a comparison group: Researchers will compare the digital intervention plus TAU group to the TAU-only group to see if adding the digital intervention significantly improves NSSI symptom reduction, depressive symptoms (HAMD-24 response rate), and long-term outcomes.

Participants will:

Undergo baseline assessments including blood sampling (inflammatory and endocrine markers, routine biochemistry), structural and resting-state functional MRI, and clinical scales (e.g., HAMD, HAMA).

Use a smartphone app for 8 weeks, completing 16 self-guided digital modules (2 per week, 15-25 minutes each) based on CBT and DBT, covering topics such as NSSI psychoeducation, safety planning, emotion regulation, distress tolerance, mindfulness, and relapse prevention.

Complete daily Ecological Momentary Assessment (EMA) questionnaires (1-2 minutes) on self-harm urge intensity, mood, and coping skills used; receive Ecological Momentary Intervention (EMI) when high urge is detected.

Receive low-intensity remote coaching (one 20-30 min onboarding call, then two brief contacts per week via text/call/email) to support app adherence.

Attend follow-up assessments at week 4, week 8 (intervention endpoint), and week 16 (study endpoint) for repeated clinical and outcome measures.

Inclusion Criteria:

• Diagnosis of Non-Suicidal Self-Injury (NSSI) according to DSM-5, confirmed by two psychiatrists with senior professional titles.
• Adolescents aged 12-25 years, any gender.
• Willing to participate voluntarily and with good insight.

Exclusion Criteria:

• Presence of severe mental disorders (e.g., schizophrenia, schizoaffective disorder, substance use disorder, intellectual disability).
• Major central nervous system diseases (e.g., history of head trauma or infection, intracranial tumor, cerebrovascular disease, epilepsy).
• History of major physical diseases (e.g., malignancy, myocardial infarction, liver or kidney dysfunction).
• History of abuse of sedative-hypnotics, alcohol, or other psychoactive substances.
• History of suicide attempt, current high suicide risk, or current suicidal behavior/ideation.
• Pregnancy or breastfeeding.