Non-Suicidal Self-Injury in Adolescents With Major Depressive Disorder: The Role of Beta-Endorphin, Psychological Pain, and Anhedonia
Background: A substantial proportion of adolescents with major depressive disorder (MDD) engage in non-suicidal self-injury (NSSI); however, the biological and psychological factors differentiating those with and without NSSI remain poorly characterized. This study aimed to investigate whether serum beta-endorphin levels, psychological pain, and anhedonia differ between these groups and to explore their associations with the presence of NSSI. Methods: The study sample comprised adolescents prospectively recruited during the study period and diagnosed with MDD according to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, Text Revision (DSM-5-TR) criteria. Participants were categorized into adolescents with NSSI (NSSI+) and those without NSSI (NSSI−). Assessments included the Children’s Depression Inventory (CDI), Psychache Scale (PAS), and Snaith-Hamilton Pleasure Scale (SHAPS). Serum beta-endorphin levels were measured using enzyme-linked immunosorbent assay (ELISA) from blood samples collected after an overnight fast. Results: The study cohort consisted of 104 adolescents with MDD, including 52 participants in the NSSI+ group and 52 in the NSSI− group. The sample comprised 85 females (81.7%) and 19 males (18.3%). Compared with the NSSI− group, adolescents in the NSSI+ group demonstrated significantly lower serum beta-endorphin levels and significantly higher levels of depressive symptoms, psychological pain, and anhedonia (all p < 0.05). In multivariable analyses, greater depression severity, higher psychological pain, and lower beta-endorphin levels were independently associated with the presence of NSSI. Exploratory mediation analyses suggested an indirect association between depression severity and NSSI through psychological pain. Conclusions: These findings highlight the relevance of both psychological and neurobiological factors in NSSI among adolescents with MDD and suggest that an integrated assessment of these factors may help identify adolescents at increased risk of this form of self-harm.