Testing Phenotypic Models of Posttraumatic Stress Disorder and Alcohol Use Disorder Comorbidity Using Longitudinal Registry Data

Objective: Two predominant phenotypic models of causality exist to explain the high co-occurrence of posttraumatic stress disorder (PTSD) and alcohol use disorder (AUD): the self-medication and susceptibility models. Population-based longitudinal studies that simultaneously examine both models are needed. Thus, the goal of the present study is to test these models using the Swedish National Registries. Method: Registries were used to conduct longitudinal Cox proportional hazard models (n approximate to 1.5 million) and cross-lagged panel models (N approximate to 3.8 million) with follow-up periods of similar to 23 years. Results: Covarying for cohort and socioeconomic status, Cox proportional hazards model results found strong support for the self-medication model. Results showed that PTSD predicted increased risk for AUD among both men (HR = 4.58 [4.42, 4.74]) and women (HR = 4.14 [3.99, 4.30]), significantly more so for men (interaction HR = 1.11 [1.05, 1.16]). Support was also found for the susceptibility model, although the effects were lower in magnitude than those for the self-medication model. AUD increased risk for PTSD among men (HR = 2.53 [2.47, 2.60]) and women (HR = 2.06 [2.01, 2.12]), and significantly more so for men (interaction term HR = 1.23 [1.18, 1.28]). Cross-lagged model results of simultaneously testing both models found support for bidirectionality. The PTSD-to-AUD paths and the AUD-to-PTSD paths were of modest effect for men and women. Conclusions: The results from both complementary statistical approaches demonstrate that the models of comorbidity are not mutually exclusive. Although the Cox model results evidenced more support for the self-medication pathway, the cross-lagged model results suggest that the prospective relationships between these disorders are nuanced across development.