Alcohol and cannabis use among college students: Substitutes or complements?
Introduction
For nearly 30 years, economists have debated whether alcohol and cannabis act as substitutes or complements to one another. In a substitute relationship, factors that inhibit availability of one substance, such as increased price or legal restrictions, lead to increases in use of the other (as in the above quote regarding hashish restrictions in Turkey). In a complementary relationship, however, factors that influence the availability of one substance have a parallel effect on use of the other (e.g., decriminalization of cannabis leading to increased alcohol consumption; Cameron & Williams, 2001). Implicit in these competing hypotheses are untested assumptions about how individuals behave with regard to alcohol and cannabis use. The substitution hypothesis assumes that substance-using individuals consume the more readily available drug and neglect the less available one. In such instances individuals may have instrumental reasons for using (e.g., self-medication, tension reduction, or stress dampening; Greeley, J. and Oei, T., 1999, Khantzian, E. J., 1997, Sher, K. J., et al., 2007) that they fulfill through the most convenient means (Stone & Kennedy-Moore, 1992). The complement hypothesis, however, assumes that individuals tend to use alcohol and cannabis together within a fixed, limited time period (e.g., during the same evening). In this case, substances may be part of a common social experience (as eloquently related in Snoop Dogg's “Gin and Juice”) or produce desired interactive effects (e.g., euphoria). Limiting availability of one substance, therefore, inadvertently cuts off access to the other substance or makes it less desirable.
Understanding the relation between alcohol and cannabis is key to predicting the overall impact on public health that may result due to changes in substance use policy, which is especially important in light of increasingly liberal attitudes toward cannabis legalization (Vitale, 2014). While support exists for both substitute and complement relations, evidence for each stems mainly from macro-level economic or epidemiological data; no research to date has examined the assumptions underlying these hypotheses at the individual level. This is the first study, therefore, to assess whether alcohol and cannabis serve as substitutes or complements during discrete episodes of substance use. We tested these competing hypotheses among United States (U.S.) college students, as alcohol and cannabis are the most commonly used substances on college campuses (Arria, A. M., et al., 2008, Caldeira, K. M., et al., 2008, Knight, J. R., et al., 2002, Wechsler, H., et al., 2002), and over one-quarter of students co-use these substances (Shillington & Clapp, 2006). Moreover, students who use alcohol or cannabis report an array of academic and social problems stemming from their use (Arria, A. M., et al., 2013, Caldeira, K. M., et al., 2008, Merrill, J. E. and Read, J. P., 2010). Findings from this sample, therefore, would be particularly informative for developing policies and interventions to curb substance use on college campuses.
Multiple studies have supported the substitution hypothesis by showing that policy changes that restrict access to one substance predict increased use of the other. For example, raising the minimum legal drinking age to 21 has been associated with increased cannabis use among U.S. high school seniors (DiNardo & Lemieux, 2001). Moreover, data from the National Survey of Drug Use and Health showed that U.S. alcohol use tends to spike at age 21 (the minimum legal drinking age), whereas cannabis use shows a stark decrease and steady decline at age 21 (Crost & Guerrero, 2012). Increases in the price of alcohol, likewise, have been linked to increased cannabis use in Australia (Cameron & Williams, 2001). In the reverse direction, decriminalizing cannabis use in the U.S. has been associated with decreased drinking (Saffer & Chaloupka, 1999), and legalizing medical marijuana predicted a nearly 15% decrease in alcohol-related traffic fatalities in the 3 years post-legalization (Anderson, Hansen, & Rees, 2013).
Evidence from the coping literature suggests that substitution may be most likely to occur among those who use alcohol or drugs to cope with negative affect. The desire to alleviate or numb unpleasant feelings is a key motivation for both cannabis and alcohol use (Simons, Correia, & Carey, 2000). Multiple theories of alcohol use posit that drinking is often a means of reducing stress or tension, alleviating negative affect, or self-medicating (Cooper et al., 1995, Greeley, J. and Oei, T., 1999, Khantzian, E. J., 1997, Sher, K. J., et al., 2007). Likewise, cannabis appears to be used primarily as a means of tension-reduction or self-medication, as it is anxiolytic (Bergamaschi, M. M., et al., 2011, Crippa, J. A., et al., 2011) and reasons for using such as relaxation and stress-reduction are frequently reported (Beck, K. H., et al., 2009, Brodbeck, J., et al., 2007, Lee, C. M., et al., 2007). Importantly, college students are at particular risk for using substances to cope (Park & Levenson, 2002), which heightens their risk for substance-related problems (Cooper et al., 1995, Simons, J. S., et al., 2005). Germane to our competing hypotheses, individuals who cope using one strategy tend not to engage in subsequent coping behaviors if the first action proved satisfactory (Stone & Kennedy-Moore, 1992). This finding suggests that students with a proclivity to cope using alcohol/drugs may be more likely to exhibit substitution; individual differences in coping style, therefore, emerge as an important potential moderator.
Other evidence, however, supports the complement hypothesis. For example, increases in the cost of alcohol have been associated with decreases in cannabis use among U.S. adolescents and young adults (Farrelly, M. C., et al., 1999, Pacula, R. L., 1998). Moreover, increases in alcohol prices and fines for heavy intoxication have been linked with decreased cannabis use in Australia, especially among individuals who use these substances concurrently (Williams & Mahmoudi, 2004). Of particular interest, higher alcohol prices and alcohol-restrictive policies, specifically regulating happy hours and banning alcohol on campus, have been associated with decreased cannabis use across U.S. colleges (Williams, Pacula, Chaloupka, & Wechsler, 2004).
Both physiological and social mechanisms have been proposed to explain why alcohol and cannabis might be used in a complementary fashion (Hall & Lynsky, 2005). Animal models demonstrate that most drugs produce similar reward effects in the dopaminergic system. The euphoria induced by one drug, therefore, may increase sensitivity to other substances, thus producing a pattern of complementary use. Moreover, decreased use of one drug could extinguish reward associations common across substances. It is also likely that alcohol and cannabis use occur in shared social settings where co-use becomes more likely due to shared availability. Given that social motives underlie much substance use on college campuses (Beck, K. H., et al., 2009, Christiansen, M., et al., 2002, Lee, C. M., et al., 2007), one may expect complementary use as part of this social milieu.
The ambivalence of the evidence—including studies that indicate asymmetrical, limited, or non-existent associations between alcohol use and other drug consumption (Krauss, M. J., et al., 2015, Petry, N.M., 2001, White, H. R., et al., 2015)—calls for further research using different methodologies to understand these relations. Examining these hypotheses at the individual level represents such an advance in our understanding. Although economic theories assume an individual-level association between these two substances, analyses at these more macro-levels cannot support such interpretations. Furthermore, both hypotheses may be true under certain circumstances, and within-person analyses present a better opportunity to explore individual differences that may shed light on when and for whom each hypothesis is correct. Identifying how efforts to curb substance use may be received by different subgroups is paramount to designing policies and interventions that provide the greatest benefit to the widest audience.
The goal of the current study, therefore, was to examine associations between proximal use of both alcohol and cannabis in a substance-using, U.S. college sample, as well as how this relation differs by individuals' general motivation to use substances to cope with stress. According to the substitution hypothesis, on evenings when students consume more alcohol than usual, we would expect to see lower odds of using cannabis. The complement hypothesis, however, would predict that on evenings of higher-than-usual alcohol use, the odds of cannabis use would be greater. Moreover, we expect to find stronger evidence of substitution among students who report using alcohol/drugs to cope. To test these hypotheses, we conducted a 30-day online daily diary study, a design well-suited for capturing discrete behaviors such as cannabis and alcohol use that tend to be memorable and time-limited (Gunthert & Wenze, 2012).
Section snippets
Participants
The institutional review board at the University of Connecticut—a large, rural, state university in the northeastern U.S—approved all procedures. From 2008 to 2012, we recruited 1818 students through the undergraduate psychology participant pool and campus-wide emails. Eligible students were at least 18 years old, had consumed alcohol at least twice in the past 30 days, and had never undergone treatment for alcohol problems (measured during prescreening). Students were excluded from analyses if
Descriptive statistics
Students in the final sample used cannabis on an average of 3.2 evenings during the study (SD = 5.5, range: 0–29), consumed alcohol on an average of 6.7 evenings (SD = 4.3, range: 0–29), and drank an average of 6.3 drinks per episode (SD = 3.9, range: 0–32). Furthermore, students used both alcohol and cannabis during the same evening an average of 1.3 times during the study (SD = 2.3, range: 0–15). As displayed in Table 1, men were heavier substance users than women across all measures of daily alcohol
Discussion
Understanding whether alcohol and cannabis act as substitutes or complements is necessary for developing policies and interventions to curb substance use. As a novel approach we looked for evidence for these hypotheses using a daily diary survey of substance-using, U.S. college students. Our results generally support earlier findings that college students engage in complementary use of alcohol and cannabis (Williams et al., 2004). Higher overall levels of alcohol consumption, as well as higher
Conclusion
These findings underscore the need to examine questions, such as the substitute versus complement hypotheses, using varied methodologies in order to fully understand complex behaviors such as substance use. Furthermore, this research highlights the need to consider the motives underlying college students' substance use before proceeding with changes in policy or interventions. Future micro-level studies are needed to explore how individuals use multiple substances in their day-to-day lives, and
Role of funding sources
Funding for this study was provided by NIAAA 5P60-AA003510, and preparation of this manuscript was supported by NIAAA 5T32-AA07290. NIAAA had no role in the study design, collection, analysis or interpretation of the data, writing the manuscript, or the decision to submit the paper for publication.
Contributors
Ross E. O'Hara performed the statistical analysis, conducted the literature search, and led the writing of the manuscript. Stephen Armeli and Howard Tennen designed the study, oversaw the collection of data, and revised the manuscript. All authors have contributed to and approve the final manuscript.
Conflict of interest
The authors declare that they have no actual or perceived conflicts of interest to report.
Acknowledgments
This research was supported by grant 5P60-AA003510, and preparation of this manuscript was supported by grant 5T32-AA07290, both from the National Institute on Alcohol Abuse and Alcoholism. The authors wish to thank Marcella H. Boynton for assistance with data analysis and Jesse J. Jungkurth for assistance with background research.
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Ross E. O′Hara is now at Persistence Plus, LLC, Boston, MA 02129, USA.