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Associations of personality traits with marijuana use in a nationally representative sample of adolescents in the United States

Introduction Identifying adolescents at risk for marijuana use who can be targeted for intervention efforts is critical. Certain personality traits are strongly associated with substance use, including marijuana use. We investigated the associations of impulsivity (and its subscales sensation seeking and lack of planning), aggression, and neuroticism with marijuana use (lifetime and frequency of past 12-month use) in a national sample of adolescents. Methods We used data from the National Comorbidity Survey: Adolescent Supplement, a nationally representative, cross-sectional study of 8495 U.S. adolescents aged 14 to 18 years. We calculated adjusted prevalence ratios and odds ratios to assess associations of the five personality scales with lifetime use and frequency of past 12-month use and examined gender as a potential moderator of these associations. Results Each of the personality traits was positively associated with lifetime use (all p < 0.001). Impulsivity (the total scale and both subscales) and aggression (all p < 0.05) were positively associated with frequency of past 12-month use. The neuroticism–lifetime use association was stronger among girls (p < 0.001) than boys (p < 0.05), and the associations of impulsivity and lack of planning with frequency of use were significant only among girls, with moderate female users reporting higher levels of the personality scales than infrequent users (both p < 0.01). Conclusions Our study highlights the potential importance of identifying personality traits, specifically disinhibition-related traits such as impulsivity and aggression, to reduce and prevent adolescent marijuana use.


Study design and participants
The NCS-A (2001NCS-A ( -2004 (Kessler, Avenevoli, Costello, et al., 2009;Kessler, Avenevoli, Green, et al., 2009;Merikangas et al., 2009) is a nationally representative, cross-sectional dataset containing information on prevalence and correlates of major mental disorders for 10,148 U.S. adolescents aged 13 to 18. We excluded 13 year olds because they had very low levels of marijuana use, yielding a sample of 8495 adolescents. We received authorization to access restricted NCS-A data from the Interuniversity Consortium for Political and Social Research and also obtained university IRB approval.

Marijuana use
Interviewers asked, "Have you ever used marijuana or hashish, even once?", to determine lifetime marijuana use (yes: n = 2214, never: n = 6262). For frequency of past 12-month marijuana use, interviewers asked "How often did you use marijuana or hashish in the past 12 months-nearly every day, 3 to 4 days a week, 1 to 2 days a week, 1 to 3 days a month, or less than once a month?" to adolescents who responded affirmatively to marijuana use in the past 12 months (n = 1379). We categorized the data into three groups: frequent use (nearly every day or 3-4 days a week: n = 380), moderate use (1-2 days a week or 1-3 days a month: n = 410), and infrequent use (less than once a month: n = 580).
We separately assessed sensation seeking and lack of planning-subscales of ZKPQ impulsivity-to better understand the "active ingredients" of impulsivity, as evidence for the association of impulsivity and marijuana use among adolescents is mixed, possibly due to differential associations of separate features of impulsivity with marijuana use (VanderVeen et al., 2016).

Statistical analyses
Lifetime prevalence of marijuana use and frequency of past 12month marijuana use were dependent variables. Impulsivity, sensation seeking, lack of planning, aggression, and neuroticism were independent variables; each was examined in a separate regression model.
We calculated descriptive statistics for age, race/ethnicity, gender, and parent education and identified their associations with the personality scales and marijuana use variables using weighted Chi-square and adjusted Wald tests. We used generalized linear modeling to calculate adjusted prevalence ratios in assessing associations between the five personality scales and lifetime use. We used multinomial logistic regression to calculate relative risk ratios in examining associations between the five personality scales and frequency of use. We adjusted for age, race/ethnicity, gender, and parent education, as these variables were associated with substance use in previous studies (Dierker et al., 2012;Keyes et al., 2015;Muro & Rodríguez, 2015). To examine gender as a potential moderator, we created terms to represent the interaction between each personality scale and gender and entered these interaction terms into our regression models. We planned gender-stratified analyses in the event that the coefficient for an interaction term was significant. As < 1% of responses were missing, we used listwise deletion by default to handle missing data. Complex survey weights were applied prior to analyses to account for the NCS-A sampling method. Statistical significance was set at p-values < 0.05. Analyses were conducted using Stata13 (StataCorp, 2013).

Sample characteristics
Adolescents aged 15 and older (χ 2 = 71.63, p < 0.001) and those whose parents had not graduated college (χ 2 = 10.55, p < 0.001) were more likely to report lifetime marijuana use. More boys than girls (χ 2 = 4.98, p = 0.01) and more adolescents in the "other" race/ethnicity group than their non-Hispanic White counterparts (χ 2 = 3.03, p = 0.03) reported high frequency of past 12-month marijuana use.
As displayed in Table 1, impulsivity-lack of planning differed by age (p < 0.05), impulsivity (total and both subscales) and neuroticism differed by gender (p < 0.001), impulsivity (total and both subscales) differed by race/ethnicity (p < 0.05), and impulsivity-lack of planning, aggression, and neuroticism differed by parent education level (p < 0.05).

Personality scales and marijuana use
All five personality scales were positively associated with lifetime prevalence of marijuana use (all p < 0.001). Impulsivity (including both sensation seeking and lack of planning), and aggression were positively associated with higher frequency of past 12-month marijuana use (all p < 0.01) (see Table 2).

Discussion
We examined associations of personality scales with lifetime marijuana use and frequency of past 12-month marijuana use in a nationally representative sample of U.S. adolescents. Each personality scale showed small but significantly positive associations with lifetime use, indicating higher levels of impulsivity, aggression, and neuroticism may distinguish adolescents who have ever used marijuana from those who have not. Impulsivity and aggression but not neuroticism were positively associated with frequency of use, suggesting adolescents with higher levels of impulsivity and aggression were more frequent users of marijuana than their peers without such tendencies. Our moderation analyses showed that the association of neuroticism and lifetime use was stronger among girls than boys, and the association of impulsivity (the total impulsivity score and the lack of planning subscale) with frequency of use was significant for girls but not boys, with significant associations for girls who reported moderate but not infrequent use.
Impulsivity and aggression were significantly associated with marijuana use. Our findings are similar to those of previous studies in nonrepresentative samples that assessed lifetime use (Malmberg et al., 2012), past 12-month use (Muro & Rodríguez, 2015), and past 30-day use (Kong et al., 2013). We also found neuroticism was not associated with frequency of marijuana use and that the association of neuroticism with lifetime use was not as robust as those of impulsivity and aggression with lifetime use. These results are similar to a recent metaanalysis that showed strong associations of both low conscientiousness (i.e., high impulsivity) and low agreeableness (i.e., high aggression) but relatively weak associations of neuroticism with adult substance use disorders. Our findings contribute to the current efforts in developing a comprehensive developmental model of marijuana use, as our findings are consistent with a recent theoretical model that argues for a crucial role of disinhibition-related traits, such as impulsivity and aggression, in substance use and other externalizing behaviors as compared with a key role of neuroticism in internalizing behaviors (Clark & Watson, 2008;Krueger, Markon, Patrick, Benning, & Kramer, 2007).
Boys reported higher impulsivity and more frequent use of marijuana than girls. Impulsivity and lack of planning were only associated with frequency of use among girls, with moderate female users reporting higher levels of these personality characteristics than infrequent users. Our findings suggest the lack of planning component of impulsivity may be more relevant for marijuana use frequency than the sensationseeking component. Girls with lack of planning capacities may benefit from a program that teaches them organization skills. One possible implication of our findings is that personality screening among adolescents may contribute to effective prevention and early intervention strategies for marijuana use. Longitudinal studies have shown that changes in personality traits can prevent future substance use in children (Hampson, Tildesley, Andrews, Luyckx, & Mroczek, 2010) and adults (Turiano, Whiteman, Hampson, Roberts, & Mroczek, 2012). Evidence suggests altering the trajectory of maladaptive personality traits is possible with cost-effective, early psychological interventions (Barlow et al., 2014;Kennedy et al., 2009;Mihalopoulos et al., 2015;Rapee et al., 2010). There is emerging evidence for personality-targeted approaches to substance use prevention, specifically in the Netherlands, England, and Australia (Conrod, 2016;Conrod, Castellanos-Ryan, & Strang, 2010;Mahu, Doucet, O'Leary-Barrett, & Conrod, 2015). The Preventure Programme screens high-risk individuals based on their personality scales and target personality-specific pathways to substance misuse (for a detailed description of the Preventure Programme, see Conrod, 2016).
This study is limited by the fact that data on personality scales and marijuana use were obtained via self-report. In addition, we cannot make causal inferences about the personality-marijuana use relationship as the NCS-A is cross-sectional in design. However, findings from several prospective studies indicate that maladaptive personality traits are likely to develop before substance use initiation and may predict maintenance and treatment outcome (Bogg & Roberts, 2013;Hengartner, Kawohl, Haker, Rössler, & Ajdacic-Gross, 2016;Lahey, 2009).

Conclusions
Our study highlights the potential importance of identifying personality traits, specifically disinhibition-related traits such as impulsivity and aggression, to reduce and prevent adolescent marijuana use. Given emerging evidence for benefits of personality-informed interventions in delaying the onset of or reducing marijuana use among non-U.S. adolescents, we recommend exploring implementation of such interventions in the U.S. Mindfulness-based interventions that promote self-regulation may also be promising in this context. Research has identified an inverse relationship between impulsivity and trait mindfulness (Murphy & MacKillop, 2012;Peters, Erisman, Upton, Baer, & Roemer, 2011) and supported the effectiveness of a mindfulness program in lowering impulsivity and aggression among high school students with behavioral issues (Franco, Amutio, López-González, Oriol, & Martínez-Taboada, 2016). Future research should explore whether such strategies could also be useful in preventing adolescent marijuana use.