This exploratory study assessed sociodemographic, psychiatric, and personality variables among medical students and found independent associations of specific personality traits with at-risk drinking and current cannabis use. Measures of model fit demonstrated improvements in discriminatory and explanatory ability when personality variables were added to basic models with sociodemographic and psychiatric variables, but as a whole, these increments were modest.

These findings should be interpreted considering some limitations. For example, the cross-sectional design of the study precludes any conclusions about causality. The non-random nature of the sampling strategy, with data obtained only from students attending classes, may have led to underrepresentation of students with greater absenteeism or with disabling psychiatric symptoms. Psychiatric measures were obtained by brief, self-report symptom scales, without any formal diagnosis using structured interviews, and encompassed only highly prevalent problems, such as anxiety, depression, and use of alcohol, cannabis, and tobacco; this approach limits conclusions on the role of psychiatric comorbidities in the outcomes of interest. Finally, the relatively high prevalence of missing data for income and BFI measures may have had a relevant impact on the power of analyses. Despite these limitations, this study expands current knowledge on substance use among medical students, particularly regarding the quantitative role of personality traits of different personality theories.

The association patterns in the models which included only sociodemographic and psychiatric variables remained after adding personality variables, with the exception of the association of at-risk drinking with university when BIS/BAS variables were added. The association between at-risk drinking and female gender seems paradoxical at first glance, as males generally consume more alcohol. However, this could be explained by the different cutoff points (which are justified by gender differences in alcohol metabolism) and perhaps reflects the general trend of approximation of alcohol consumption between the genders observed in recent decades.2 Of note, no independent association was found between gender and current cannabis use, which may also reflect this trend. Thus, female students may now constitute a group at risk of harmful drinking. At-risk drinking was also independently associated with not being married/in a domestic partnership; this result replicates in medical students a longstanding, consistent finding of other populations.21

Studying at University B (private) was independently associated with at-risk drinking in the models which included sociodemographic and psychiatric variables (model #1), as well as BFI measures (model #2). However, the association was not independent of BIS/BAS measures (model #3), suggesting a more complex relationship between these variables. The already cited nationwide Brazilian survey of university students3 found a somewhat complex scenario when comparing public and private institutions: in the latter, a higher prevalence of last-month cannabis use and high-risk drinking was observed, whereas binge drinking was more frequent in public institutions. Our results are partially aligned with these findings. Specific institutional and environmental factors have been shown to influence drinking habits among college students.22 Our analyses disaggregating data by university suggest that these differences are related to sociodemographic factors, whereas the role of personality tends to be stable across institutions.

The lack of association between PHQ-4 scores and at-risk drinking or current cannabis use is noteworthy, considering the well-known comorbidity of substance use disorders and depressive and anxiety disorders. This may reflect the aforementioned limitations of using screening instruments, but agrees with previous research on medical students showing this lack of association23 or association with alcohol dependence, but not alcohol abuse.24 Community studies have also shown that comorbidity with depressive and anxiety disorders is most marked in heavy users of alcohol or cannabis.25,26

At-risk drinking and current cannabis use were independently and substantially associated with each other in all analyses. In fact, alcohol consumption as a numerical measure was the only non-personality variable independently associated with current cannabis use. Data from college students in the United States in recent decades have shown a gradual dissociation in the prevalence of use of these substances, with increased use of cannabis and decreased use of alcohol.2 However, the use of alcohol and cannabis simultaneously (at the same time) or concurrently (on different occasions) remains very common and has been associated with additional negative social and health outcomes (such as driving under the influence, mood and anxiety disorders) than isolated use of either substance.27 It is noteworthy that knowledge about interventions to mitigate the use of alcohol when consumed simultaneously or concurrently with other drugs is limited.28

The associations of personality traits with at-risk drinking and current cannabis use in the present study were mostly in agreement with the literature. The reverse association of conscientiousness with both outcomes is largely consistent with meta-analyses of subjects with substance use disorders8,29 and large studies of non-clinical samples.30,31 Another finding that replicated the literature is the association of the outcomes of interest with greater BAS sensitivity.32 In the present study, only the fun-seeking subscale of the BAS showed an independent association with at-risk drinking and current cannabis use. This is consistent, for example, with research on college students which reported associations with greater alcohol use, frequency of binge drinking, and number of illicit drugs already used,33,34 as well as a large epidemiological study which found BAS fun-seeking to be a vulnerability factor for substance-related problems.35 Similarly, a recent systematic review showed associations of binge drinking with higher impulsivity and sensation-seeking, as well as with lower conscientiousness.36 Thus, lower conscientiousness and higher BAS sensitivity (fun-seeking in particular) stand out as factors consistently associated with greater use of different substances in distinct populations. The RST postulates that the neural substrates of the BAS include mesocorticolimbic dopamine pathways.37 These pathways are conceptualized as major components of the brain reward system, and play a central role in neurobiological models of substance use disorders. The reward response has the distinct components of “wanting” (related to motivation) and “liking” (related to actual pleasure). The incentive-sensitization theory of addiction states that addiction is caused by substance-induced changes in the brain’s mesocorticolimbic circuitry, leading to amplification of the “wanting” component.38

The findings of independent, direct associations between at-risk drinking and extraversion, as well as current cannabis use and openness to experience, are not aligned with previous meta-analyses of substance use disorders.8,29 However, they are partially aligned with other studies of non-clinical samples. For example, a systematic review found a direct association between higher extraversion and binge drinking,36 and a large community-based study directly correlated cannabis use with openness to experience.31 Thus, one may speculate that clinical and non-clinical samples (such as undergraduate students) differ in their personality profile in the context of substance use, but this hypothesis remains to be directly addressed. BIS sensitivity and neuroticism are conceptually related constructs to some extent; nevertheless, in the present study, participants with at-risk drinking showed lower BIS scores, but not lower neuroticism. An association of substance use and lower BIS sensitivity has been described previously among college students.33 However, higher neuroticism in alcohol use has been found more consistently.36 In addition, higher neuroticism has been associated with several psychiatric disorders.8

Research on personality traits of medical students has focused mainly on their role in stress and academic achievement, suggesting that conscientiousness is important to success in early years, while more prosocial traits are relevant in later clinical years.39 Consistently, in our study conscientiousness was inversely related to potentially harmful behavioral outcomes. While studies relating personality traits and substance use have been frequently conducted among college students, research specifically addressing medical students in this regard is much scarcer. A nationwide, prospective study in Norway40 assessed medical students at different time points and reported that impulsiveness at the first time point predicted binge drinking at the second time point. Another study in England23 found direct associations between a measure of the psychoticism construct in Eysenck’s personality model (which is considered inversely related to agreeableness and conscientiousness in the Five-Factor Model) and alcohol and illicit drug intake. As in the present study, an investigation conducted in another region of Brazil41 evaluated Big Five traits related to alcohol dependence in medical residents and found an independent direct association with extraversion.

A systematic review of Big Five traits across different academic majors reported consistent group differences with medium to high effect sizes.42 Therefore, understanding the role of personality traits in substance use in specific student populations may have implications for mitigation strategies. At the collective level, personality traits may inform the design of preventive campaigns. For example, dramatic portrayals of the possible consequences of cannabis use have been shown to reduce last-month cannabis use, specifically in youths with high sensation-seeking.43 At the individual level, measures of personality traits could be used to identify individuals at risk of substance-related problems and to develop specific interventions. Interventional studies conducted to date generally found positive results with moderate effect sizes for interventions with psychoeducational, motivational, and cognitive-behavioral components, addressing traits of impulsivity, sensation-seeking, anxiety, and hopelessness.44

Our results showed independent associations of specific personality traits with the outcomes of interest, but with modest effect sizes. At first glance, this suggests that taking personality into account in preventive or therapeutic approaches would have a modest impact as well. However, we assessed a non-clinical sample, and the role of personality traits may differ in medical students with a formal diagnosis of substance use disorders. This is a relevant topic to be addressed by future studies. On the other hand, our results also demonstrated modest effect sizes for sociodemographic and psychiatric variables. This is consistent with the idea that preventive and therapeutic approaches should consider the multifactorial, complex nature of substance-related problems.45 Although we found stability of the role of personality traits in at-risk drinking across the two participant universities, a “one-size-fits-all” approach does not seem appropriate, as research also suggests that medical school specificities are important.22 For example, subgroups within a medical school could be identified for specific interventions, as illustrated by our results showing that living alone was a risk factor for at-risk drinking in only one of the universities.

To conclude, substance misuse is an important issue to be addressed in medical student populations, as it may be a gateway to substance use disorders and other substance-related problems. This may ultimately impact public health due to the specific implications of substance-related problems among physicians, which range from difficulties to seek treatment to impaired patient care and legal problems. Our findings and the literature discussed above indicate that personality traits have a significant role in substance use among medical students, and may be useful to inform preventive and therapeutic approaches. Evidence-based interventions informed by personality characteristics, however, are a relatively new area of research, and more studies in specific populations are needed. Personality traits linked to substance misuse may be more stable across institutions than sociodemographic factors, but specific local characteristics should not be overlooked. Medical schools can use evidence from the literature, together with their own quantitative or qualitative data, to define strategies consistent with their realities.