Health Disparities
The Price of Delay: Interactions Between Addiction, Depression, and Inequality Youngseo Cheon* Youngseo Cheon Cheon Department of Epidemiology, College of Public Health & Health Professions and College of Medicine, University of Florida, Gainesville, FL, USA
Objectives: To examine whether delayed therapy due to treatment cost is associated with the co-occurrence of substance use and depression in U.S. adults and whether these conditions interact synergistically on the additive scale, consistent with a syndemic framework.
Methods: We analyzed data from the 2024 National Health Interview Survey Sample Adult (n=19,054). Weighted group comparisons and logistic regression models were used to examine associations between delayed therapy due to cost and co-occurrence of conditions. Additive interaction was evaluated using the relative excess risk due to interaction (RERI), attributable proportion (AP), and synergy index (SI), with odds ratios used as approximations of risk ratios.
Results: Overall, 4.2% of adults reported co-occurring substance use and depression. Delayed therapy due to cost was strongly associated with co-occurrence (AOR = 2.35; 95% CI: 1.90, 2.90). Women had more than twice the odds of co-occurrence compared to men (AOR= 2.09; 95% CI: 1.73, 2.53). Additive interaction analyses showed significant evidence of positive interaction between delayed therapy and female sex (RERI = 1.30; AP = 0.27; SI = 1.51), indicating a more-than-additive joint effect. In contrast, delayed therapy and low educational attainment demonstrated a sub-additive interaction (RERI = –1.19), despite each factor being independently associated with higher risk; however, the interaction was not statistically significant.
Conclusion: Delayed therapy due to cost is a robust correlate of the co-occurrence of substance use and depression. Additionally, the effect of delayed therapy increases synergistically among women, reflecting stronger joint effects in female populations. These findings suggest that social barriers to care intersect with gendered vulnerabilities and underscore the importance of a syndemic-informed approach that recognizes clustered social and behavioral risks.