Heterogeneous and Joint Developmental Trajectories of Non‐Suicidal Self‐Injury and Depression in Emerging Adulthood: The Role of Interpersonal Dynamics

Non-suicidal self-injury (NSSI) and depression frequently co-occur among emerging adulthood, yet how they co-develop over time in response to interpersonal stress and which social factors shape this process remain unclear. Understanding these joint trajectories and their interpersonal predictors is critical for early identification and effective intervention. This longitudinal study examined how NSSI and depression co-develop in Chinese college students and tested four interpersonal predictors (parent-child, peer, teacher-student, and dormitory relationships) via latent class growth analysis (LCGA). Three-wave data over 12 months revealed two NSSI trajectories (Low-Stable and High-Decreasing) and three depression trajectories (Low-Stable, Moderate-Fluctuating, High-Stable). Joint trajectories of NSSI and depression formed two patterns: Low-Comorbidity-Stable and Moderate-Comorbidity -Decreasing. Parent-child, peer, and dormitory relationships each predicted lower-risk trajectories, with dormitory ties exerting the strongest influence and suggesting that dormitory environments serve as crucial intervention targets. In contrast, teacher-student relationships had no significant effect, a finding that warrants further investigation. Findings indicate that interpersonal stressors and the buffering effect of supportive relationships shape stress-related health outcomes in emerging adults, with implications for interpersonal-focused campus prevention strategies.