Post-traumatic stress disorder and drug use disorder: examination of aetiological models in a Swedish population-based cohort.

Background

There are two primary phenotypic models of comorbidity between post-traumatic stress disorder (PTSD) and drug use disorder (DUD), i.e. self-medication (PTSD precedes and causes DUD) and susceptibility (DUD precedes and causes PTSD). We sought to clarify the longitudinal relationship between PTSD and DUD, while examining sex differences.Method: We used approximately 23 years of longitudinal data from Swedish population registries to conduct two complementary statistical models: Cox proportional hazard models (N ≈ 1.5 million) and a cross-lagged panel model (N ≈ 3.8 million).

Results

Cox proportional hazards models, adjusting for cohort and socioeconomic status, found strong evidence for the self-medication hypothesis, as PTSD predicted increased risk for DUD among both women [hazard ratio (HR) = 5.34, 95% confidence interval (CI) 5.18, 5.51] and men (HR = 3.65, 95% CI 3.54, 3.77), and moreover, that the PTSD to DUD association was significantly higher among women (interaction term 0.68, 95% CI 0.65, 0.71). The results of the susceptibility model were significant, but not as strong as the self-medication model. DUD predicted risk for PTSD among both women (HR = 2.43, 95% CI 2.38, 2.50) and men (HR = 2.55, 95% CI 2.50, 2.60), and HR was significantly higher in men (interaction term 1.05, 95% CI 1.02, 1.08). Investigating the pathways simultaneously in the cross-lagged model yielded support for both pathways of risk. The cross-paths instantiating the susceptibility model (0.10-0.22 in females, 0.12-0.19 in males) were mostly larger than those capturing the self-medication model (0.01-0.16 in females, 0.04-0.22 in males).

Conclusions

We demonstrate that the relationship between PTSD and DUD is bidirectional, with evidence that future research should prioritize examining specific pathways of risk that may differ between men and women.