Interpersonal Determinants of Suicide Risk Among Young Adults: A Cross-Cultural Study

(1) Background: Understanding suicide risk across cultures requires examining both universal and culturally specific factors that inform assessment and intervention. This study explores the influence of interpersonal variables-such as interpersonal competence, perceived social support, and constructs from the Interpersonal Theory of Suicide (ITS)-on suicidal behaviour in two culturally distinct samples: young adults from Spain and Japan. (2) Methods: A total of [437] participants (Spanish sample: <i>n</i> = 260; Japanese sample: <i>n</i> = 177) completed validated measures assessing suicide risk, depression, perceived burdensomeness, thwarted belongingness, acquired capability for suicide, interpersonal competence, and perceived social support. Moderated mediation and SEM comparative analyses were conducted to identify predictors of suicide risk in each cultural context. (3) Results: Social support was a consistent protective factor against depression and suicidal ideation, and interpersonal competence showed more contextual protective effects, significant only in the Japanese sample. Perceived burdensomeness stood out as a robust predictor of depression and suicidal ideation in both samples, and suicidal ideation was strongly associated with suicidal behaviour, while acquired capability for suicide and interpersonal competence did not show a direct association with it. (4) Conclusions: The findings highlight the protective role of interpersonal competence and perceived social support in the progression to suicidal behavior, suggesting cultural similarities and differences in how these factors operate.