Context Self-medication of anxiety symptoms with alcohol, other drugs, or both has been a plausible mechanism for the co-occurrence of anxiety disorders and substance use disorders. However, owing to the cross-sectional nature of previous studies, it has remained unknown whether self-medication of anxiety symptoms is a risk factor for the development of incident substance use disorder or is a correlate of substance use.
Objective To examine whether self-medication confers risk of comorbidity.
Design A longitudinal, nationally representative survey was conducted by the National Institute on Alcohol Abuse and Alcoholism. The National Epidemiologic Survey on Alcohol and Related Conditions assessed DSM-IV psychiatric disorders, self-medication, and sociodemographic variables at 2 time points.
Setting The United States.
Participants A total of 34 653 US adults completed both waves of the survey. Wave 1 was conducted in 2001-2002, and wave 2 interviews occurred 3 years later (2004-2005).
Main Outcome Measures Incident substance use disorders in participants with baseline anxiety disorders and incident anxiety disorders in those with baseline substance use disorders.
Results Logistic regression analyses revealed that self-medication conferred a heightened risk of new-onset substance use disorders in those with baseline anxiety disorders (adjusted odds ratios [AORs], 2.50-4.99 [P < .01]). Self-medication was associated with an increased risk of social phobia (AOR in baseline alcohol use disorders, 2.13 [P = .004]; AOR in baseline drug use disorders, 3.17 [P = .001]).
Conclusions Self-medication in anxiety disorders confers substantial risk of incident substance use disorders. Conversely, self-medication in substance use disorders is associated with incident social phobia. These results not only clarify several pathways that may lead to the development of comorbidity but also indicate at-risk populations and suggest potential points of intervention in the treatment of comorbidity.