Early drug use might to lead to drug addiction; the earlier individuals begin to engage in risky drug use, the more likely they are to engage in later drug abuse. Therefore, early intervention is warranted. This study explored individual differences in drug use tendencies in young and healthy adults. Specifically, I examined how self-reported emotion regulation (ER) difficulties and inhibition abilities, as indexed by resting heart rate variability (HRV), might predict risky drug use tendencies in young adults. I further considered these associations stratified by women and men. Novel results showed self-reported (or perceptions of) difficulties in ER were associated with higher drug usage in the full sample and this association was significantly stronger in women than men. Among the six different facets of ER difficulties, only those related to impulse control difficulties and limited access to ER strategies were most related to risky drug usage in women but not men. The other four facets of ER difficulties were not significantly different between men and women. An indirect association was found between resting HRV and drug use, mediated by self-reported difficulties in ER, particularly in women. Overall, results indicate that lower HRV and difficulties in ER indirectly and directly, respectively, predict risky drug use in women. These data are in line with research suggesting women might engage in risky drug use primarily for stress regulation while men might engage in risky drug activity irrespective of both resting HRV and difficulties in ER. Clinical implications are discussed.

This dissertation investigates the relationship between resting heart rate variability (HRV) and substance use, including the potential moderating roles of gender and race. Study 1 analyzes data from the Midlife in the United States Study (MIDUS) to examine cross-sectional associations between resting HRV and substance use, exploring potential gender differences and mediation effects involving emotion regulation (ER). Results indicate that men reported higher emotion control, alcohol consumption, and cigarette smoking compared to women. Higher resting HRV was associated with increased alcohol consumption, particularly in women, while no significant link was found between resting HRV and cigarette smoking. Mediation and moderation models did not yield significant findings. Study 2 utilizes data from the Augusta Heart Study to examine associations between resting HRV in late adolescence and substance use in early adulthood, again while considering gender and race. Results show that men and European Americans used more substances than women and African Americans, respectively. However, resting HRV did not predict substance use. Among African Americans, the slope between resting HRV and cigarette smoking was more positive in women than in men. These findings suggest that resting HRV may not be a particularly strong predictor of substance use but could still hold relevance in specific contexts or subgroups. Further research is needed to explore the complex interplay of factors influencing substance use behaviors. This dissertation highlights the importance of understanding various motivations for substance use and emphasizes the need for ongoing research targeting individualized treatments based on marginalized identities.