Future research should thus work on validating a vicarious racism questionnaire in order to allow researchers to properly collect much-needed data on different aspects of this construct, especially as vicarious racism becomes more pervasive in the modern era. Another limitation regards some of the study results. Although we found that the link between frequency of vicarious racism and substance use depends on ethnic identity, it is important to note that the simple effects at high and low levels of ethnic identity were not significant. Future research should examine this interaction with larger sample sizes, include a more precise measure of alcohol and marijuana use , and/or consider a manipulation of ethnic identity rather than a self-report measure.In the wake of increased legislation sanctioning the recreational and medicinal use of cannabis in the United States, there is growing interest on the impact of cannabis on other substance use, including alcohol . Alcohol consumption and related consequences are of significant public health concern, as alcohol is the 3rd leading cause of preventable death in the United States , 2013. Cannabis is frequently used with alcohol, and this co-use has been associated with increased alcohol consumption, consequences, and alcohol use disorder . Individuals with cannabis dependence have nearly double the long-term risk for experiencing alcohol related problems and are more likely to develop AUD compared to drinkers who do not use cannabis. Further, cannabis use during alcohol treatment is associated with negative alcohol-related treatment outcomes . Despite the clinical and public health risks associated with co-use, questions remain whether cannabis use acts as a substitute or complement for alcohol use , mobile shelving system and whether these patterns change over time. Regarding substitution, individuals abstinent from cannabis reported greater alcohol consumption and craving during an experimental abstinence period .

State-level policy studies also find that cannabis can function as a substitute for alcohol consumption . There is equally compelling evidence that cannabis acts as a complement to alcohol use: the majority of epidemiological studies, as well as studies examining individual-level outcomes, indicate cannabis use is related to increased consumption of alcohol . Thus, it is critical to use nuanced measurement of alcohol and cannabis use, including daily and event-level studies, in order to clarify these patterns. Rather than examine the effects of cannabis on alcohol consumption, to date most event level studies of co-use have examined outcomes and consequences related to simultaneous use of alcohol and cannabis among adolescents and college students or effects of co-use on cannabis intoxication or use . However, recent work found that daily cannabis use among veterans was associated with increased likelihood of same-day moderate drinking compared to no drinking, and same-day heavy drinking compared to moderate drinking . Similarly, the first longitudinal study examining the effect of cannabis use on alcohol use found that cannabis use days were associated with more drinks and higher estimated blood alcohol concentration compared to non-cannabis use days. This study also found that these associations strengthened over the course the study , suggesting the link between cannabis use at the daily level and more drinking increases over these formative years. Although compelling, data collection for this study included a sample of college students, limiting generalizability. In addition to person-level factors such as age , several moderators of the association between cannabis and alcohol use have been identified. Metrik et al. revealed that individuals with an AUD were significantly more likely to drink heavily on cannabis use days compared to drinkers without an AUD; however, individuals with cannabis use disorder were significantly less likely to drink heavily on cannabis use days. In Gunn et al , pre-college levels of alcohol use and problems predicted increased alcohol consumption on cannabis use days.

Together with clinical and epidemiological studies, this research suggests that those with problematic alcohol use or AUD are at increased risk for heavier consumption when also using cannabis. However, a potential substitution effect may be present for individuals who are using cannabis at heavy or dependent levels—specifically for those without any evidence of AUD—as their demand for alcohol may be diminished in the presence of cannabis . To further elucidate the nature of the cannabis-alcohol association, it would be informative to closely examine medicinal cannabis users, who report using cannabis at a daily or nearly daily level . Medicinal cannabis users have cited use of cannabis as a substitute for alcohol and as a way to better manage alcohol withdrawal symptoms . Among medicinal cannabis users, cannabis may be less strongly associated with increased alcohol consumption. For instance, national data suggest that medicinal users are less likely to have an AUD compared to recreational users . In a large study of veterans, those who reported cannabis use for medicinal purposes also reported using alcohol less frequently, compared to those who reported only recreational cannabis use . Finally, veterans who use cannabis recreationally report higher frequency of alcohol use and are more likely to report alcohol intoxication as a motive for cannabis use . Together, these studies suggest that medicinal users may use cannabis to reduce alcohol consumption . However, to date, there are no event or daily-level examinations of the association between cannabis and alcohol use among medicinal versus recreational cannabis users.Multilevel modeling was used to conduct all analyses as data are nested within individuals, using the lmer4 package within R . A series of linear mixed effects models tested the prediction of number of drinks by cannabis use across all days and moderation of these effects by subject-level variables .

Dependent variables in all three models were daily number of drinks as self-reported on the TLFB. All models included fixed effects of percent of cannabis use days , calculated from all TLFB days as a percentage of those days in which any cannabis was used . All models also included fixed effects of any daily cannabis use , time , baseline age, any daily cigarette use , any other daily drug use , day of the week , and random effects for individual. The initial model examining the longitudinal effect of daily cannabis use on alcohol consumption also included the interaction of time and daily cannabis use. For the model examining moderation by type of user , time and two and three-way interactions between time, type of user , and daily cannabis use were included. For the final exploratory analysis examining moderation by alcohol substitution reason among medicinal users only, time and two- and three-way interactions between time, substitution reason , and daily cannabis use were included. Due to the small number of females in the sample and the effect of sex being non-significant in all models, sex was removed from final analyses. Initial models also included marital status, race, and ethnicity, which were also non-significant and removed from final analyses.This is the first study to examine day-level associations between daily cannabis use and alcohol consumption among medicinal and recreational cannabis users. We examined: whether daily cannabis use predicted increased daily alcohol consumption across 18 months; whether recreational cannabis users would drink more on cannabis use days compared to medicinal users; and the role of cannabis as a self-reported substitution for alcohol among medicinal users. Results indicated that cannabis use was associated with higher levels of alcohol consumption at the daily level, and that this effect was consistent over time. There was also a significant moderation by type of user, in that recreational users drank more on cannabis use days compared to medicinal users. Follow-up analyses showed that among these medicinal users, those who reported more frequent use of cannabis to substitute alcohol were more likely to drink less on cannabis use days. Our findings are consistent with other studies suggesting complementary use of alcohol and cannabis among recreational users . Further, mobile racking significant negative effect of time and cannabis use on alcohol consumption was detected in our initial model, and in our second which considers type of user. However, in both models, these effects are of small magnitude, suggesting that the positive association between alcohol and cannabis use is relatively stable, but may reduce, over time. Although this is inconsistent with a recent study of college students in their first two years of school, which found a strong positive association between time and cannabis use on daily number of drinks , this discrepancy may be a function of the unique samples.

Compared to the present study sample of veterans, of which 45% and 35% had an AUD and CUD respectively at baseline, college students in their first two years of school in Gunn et al. were following a population-based trend of increased alcohol consumption during this developmental period . Our results supporting complementary use are also consistent with prospective studies that suggest cannabis use during treatment for alcohol use may result in poorer alcohol-related treatment outcomes . Taken together, although results were of relatively modest effect sizes, this daily-level study suggests that cannabis use consistently complements alcohol consumption over time among recreational users. Further, our finding that type of user moderated the effect of cannabis use on alcohol consumption helps to elucidate conflicting evidence in the field as to whether cannabis acts as a substitute or a complement to alcohol consumption . Results suggest that cannabis is more likely to act as a substitute among medicinal users, but not recreational users. These results are consistent with other survey studies suggesting that medicinal users report using cannabis as a substitute for alcohol . Overall, it may be that those who use cannabis for medicinal reasons may be less likely to experience the additional risks associated with co-use, compared to recreational users. Consistent with other studies , our sample of medicinal users were less likely to have an AUD and drank on fewer days compared to recreational users. However, our sample was also more likely to have a CUD and reported more frequent cannabis use days and couse days across the assessment period. Therefore, although medicinal users may be less likely to experience clinically significant symptoms related to alcohol use, they were more likely to meet criteria for a CUD. However, this finding should be tempered by an important consideration in the literature regarding whether assessment methods for DSM-5 CUD symptoms translate for medicinal users. For instance, Loflin et al. suggest that symptoms that assess frequency and density of cannabis use may not be as indicative of problems in medicinal users compared to recreational users. Our preliminary follow-up analyses examining the role substitution among medicinal users confirmed that those who reported using cannabis to substitute for alcohol’s effects more frequently were less likely to drink more on cannabis use days, compared to medicinal users who reported less frequent substitution. The present study has important implications for treatment and prevention. First, our results are consistent with several other recent studies of treatment samples suggesting that recreational use of cannabis is associated with increased alcohol consumption and should be avoided for those in treatment for AUD or alcohol related problems. These findings suggest caution should be taken in the wake of changes in recreational cannabis policy, as increased cannabis use could lead to increased problematic drinking among recreational users . In addition, there is a clear documented negative impact of cannabis use on AUD recovery for individuals with AUD in alcohol treatment . Medicinal cannabis users in our sample consumed alcohol less frequently than recreational cannabis users, which could be interpreted as an additional indication that medicinal cannabis may serve as a replacement for alcohol use. However, these data were drawn from an observational longitudinal study not limited to an alcohol treatment-seeking sample and should not be applied to those in treatment for alcohol misuse. Furthermore, veterans in this sample endorsed a number of conditions for medical cannabis use including anxiety, stress, PTSD, pain, depression, and insomnia . Therefore, besides using cannabis as a substitute for alcohol, there may be important additional moderators among reasons for medical cannabis use that could clarify the cannabis-alcohol co-use association.This study should be understood in the context of several limitations. First, although the TLFB has established reliability and validity, it does require retrospective recounting of substance use. As with all self-report measures, this may be subject to recall biases.