A longitudinal examination of the self-medication hypothesis: The impact of self-medication on the development of anxiety, substance use and comorbidity in a nationally representative sample

Anxiety and substance use disorders frequently co-occur in both general population and clinical samples (De Graaf et al." 2002; Grant et al., 2004; Bibb and Chambless, 1986; Mullaney and Trippett, 1979). The "self-medication hypothesis" - which states that individuals use substances as a means of anxiety reduction - is a common explanation for this phenomenon (Quitkin, 1972; Khantzian, 1985). Previous investigations into whether self-medication is causally related to the development of comorbid anxiety and substance use have generally been limited due to a lack of longitudinal, nationally representative data. Furthermore, mixed findings in the literature may be the result of inconsistencies in operational definitions of anxiety, substance use, and comorbidity. The current study examined the role of self-medication in the development of comorbidity using a longitudinal, nationally representative dataset. Additionally, a broad array of individual anxiety and substance use disorders were examined in an attempt to gain an understanding of the different pathways to comorbidity and to help clarify certain definitional inconsistencies in the literature. Self-medication at baseline was associated with a variety of anxiety and substance use disorders -- occurring both individually and together -- at follow-up three years later. Specifically, among those with no anxiety disorder, and those with substance use disorders, self-medication increased risk for the development of social phobia. Self-medication with either drugs or alcohol at baseline was also significantly associated with risk of all comorbid substance use and anxiety disorders. Finally, self-medication was associated with persistent comorbidity, substance use disorders, and social phobia. These results have important implications. Clinicians should be aware of, and inform patients about the risks of self-medication. Self-medicating clients also represent a group of individuals at risk for developing and maintaining disorders which should guide prevention and treatment strategies. Furthermore, these results serve to validate the self-medication hypothesis and illuminate the risks that this behaviour confers.