Association between cannabis use, psychosis, and schizotypal personality disorder: Findings from the National Epidemiologic Survey on Alcohol and Related Conditions
Introduction
Cannabis is the most widely used illicit substance in the United States (Substance Abuse and Mental Health Services Administration, 2010) and the most commonly used illicit drug among patients with schizophrenia. Accumulating evidence from longitudinal epidemiologic studies also suggests that cannabis use may increase the risk of schizophrenia (Andreasson et al., 1987, Tien and Anthony, 1990, Degenhardt et al., 2001, Arseneault et al., 2002, van Os et al., 2002, Zammit et al., 2002, Fergusson et al., 2003, Henquet et al., 2005), serving as a component cause of the disorder, meaning one of a constellation of complex factors that may hasten the development of psychotic symptoms while neither necessary nor sufficient to do so alone (Compton et al., 2009).
One approach to explore the relationship between cannabis use and psychotic symptoms is to examine cannabis use as a correlate of schizotypal personality disorder (SPD), characterized by a set of dimensional traits that are thought to contribute to risk for psychosis. SPD traits have been reported to be more prevalent in relatives of patients with schizophrenia (Kendler et al., 1995, Appels et al., 2004) and may share some of the same genetic underpinnings as schizophrenia (Fanous et al., 2007). Individuals with SPD also exhibit social deficits similar to, but less prominent than, those found in schizophrenia (Dickey et al., 2005).
An emerging body of research suggests an association between schizotypy and cannabis use. Several small studies of university students have found associations between cannabis use and positive schizotypal features (Williams et al., 1996, Mass et al., 2001, Nunn et al., 2001, Skosnik et al., 2001, Dumas et al., 2002, Bailey and Swallow, 2004, Schiffman et al., 2005, Barkus and Lewis, 2008, Esterberg et al., 2009, Najolia et al., 2012). One study of 40 college undergraduates found a significant positive correlation between schizotypy scores and cannabis use (Skosnik et al., 2001). Another study (Bailey and Swallow, 2004) found an association between cannabis use and the presence of positive, negative, and disorganized schizotypal traits among 60 undergraduates. However, other studies have shown that cannabis users have lower negative schizotypal traits than non-users (Nunn et al., 2001, Schiffman et al., 2005).
Understanding the relationship between cannabis use and SPD is important for enhancing our understanding of cannabis use as a risk factor for schizophrenia-spectrum disorders and has implications for prevention and treatment, especially in light of evidence showing that interventions targeting personality factors can significantly reduce substance use (Conrod et al., 2008). While studies to date provide a foundation for establishing an association between cannabis use and schizotypy, previous studies have shown both positive and negative associations between cannabis use and domains of schizotypy, as described above. Discrepancy in previous research challenges our understanding of the relationship between cannabis use and schizotypy. One possible explanation for the discrepancy in previous studies is that all of them are limited by relatively sample sizes and limited statistical power, as well as limitations in generalizability. None has examined whether the extent of cannabis use is associated with likelihood of having SPD features. We aim to clarify the discrepancy in previous research on cannabis use and schizotypy using an epidemiologic approach that extends current evidence based on small survey samples. The present study examines – in a large, representative U.S. sample – the relationship between cannabis use and both psychosis and SPD, and whether there is a dose–response relationship between the extent of cannabis use and psychosis and specific schizotypal personality traits.
Section snippets
Sample and procedures
Wave 2 of the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC) was used as the source of data. The NESARC is a large, nationally representative survey of people living in the 50 states of the U.S. and the District of Columbia, including citizens and noncitizens, aged 18 years and older (Grant et al., 2003a, Grant et al., 2003b, Grant et al., 2004, Grant et al., 2005). Wave 1 of the NESARC was conducted in 2001 and 2002 with households and non-institutional group quarters,
Results
Table 1 shows the descriptive sample characteristics of lifetime cannabis users and non-users. Compared to non-users (n = 27 025), lifetime cannabis users (n = 7 438) were significantly more likely to be male. There were also significant differences with regard to age and race. Lifetime cannabis users were more likely to be younger (30–44 years old), and they were more likely to be white compared to cannabis non-users.
Table 2 shows the percentage of lifetime cannabis users in the entire sample (n =
Discussion
This is the first population-based study to examine the association between lifetime cannabis use, self-reported history of psychotic illness or episode (SPIE), schizotypal personality disorder (SPD), and schizotypal features, further implicating cannabis use as a possible risk factor for psychosis liability. The results indicate that the risk of both psychosis and SPD increases with greater use of cannabis, in a dose-dependent manner. Compared to non-users, greater cannabis use showed
Role of funding source
This work was supported by the National Institute on Drug Abuse (DA019606, DA023200 and DA023973 to C.B. and DA007294 to F.R.L.), the National Institute of Mental Health (MH082773 and MH076051 to C.B. and MH081011 to M.T.C.), and the New York State Psychiatric Institute (C.B., F.R.L., and G.P.D.).
Contributors
GD and CB were extensively involved in the conception and planning of the focus and content of this manuscript. GD undertook the literature search and completed the first draft of the paper. SW conducted the statistical analysis for this study. GD worked closely with CB in subsequent revisions of the manuscript. MC and FL provided feedback and provided additional content to the body of the report. All authors contributed to and have approved the final manuscript.
Conflict of interest
The authors have no conflicts of interest to declare.
Acknowledgment
Original data set for the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC) is available from the National Institute on Alcohol Abuse and Alcoholism (http://www.niaaa.nih.gov).
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