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.