U.S. young adults face the largest student loan burden in history, rising income inequality, and economic uncertainty. Personal debt and other financial stressors have been associated with problematic drinking and mental health symptoms. In this paper, we investigated whether student loan debt was more strongly linked to problem drinking and mental health symptoms among those in lower positions of socioeconomic status (SES) and those who perceived greater [in]stability in their SES (SES-instability). Using data from a larger study of college graduates, we investigated SES, SES-instability, student debt, and their 2-way interactions on problematic drinking and mental health symptoms. College graduates (N = 331), who were two years post-graduation, completed measures assessing student debt, perceived SES, SES-instability, problematic drinking, and mental health symptoms (depression, anxiety, and stress). The hypotheses and data analysis plan were registered prior to conducting analyses. The expected unique, positive associations of SES-instability with problematic drinking and mental health symptoms were supported. SES was uniquely linked with problematic drinking only and in the opposite direction as predicted. Student debt was uniquely and positively linked to stress only. The expected interactions were largely supported for SES-instability and student debt—i.e., the associations of student debt with problematic drinking, anxiety, and stress were stronger (more positive) for those with greater SES-instability. The expected interactions for SES and student debt were null. Though data are cross-sectional and come from an educationally-privileged group, study findings provide preliminary evidence of links between young adult student loan debt, greater SES-instability, and their drinking/mental health.