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. Author manuscript; available in PMC: 2025 Apr 23.
Published in final edited form as: J Ethn Subst Abuse. 2023 Oct 23;24(3):607–620. doi: 10.1080/15332640.2023.2270546

Recreational Marijuana Legalization and Marijuana and Alcohol Co-Use Among Adolescents: Differential Associations Among Racial and Ethnic Groups

Grisel García-Ramírez 1,2,3, Mallie J Paschall 1, Joel W Grube 1,2, Patrice Vaeth 1, Raul Caetano 1
PMCID: PMC11035481  NIHMSID: NIHMS1941637  PMID: 37870062

Abstract

We examined associations of the 2016 legalization of recreational marijuana (RML) in California with marijuana and alcohol co-use among race/ethnic groups using successive cross-sections from 7th, 9th, and 11th graders (N=3,319,329) in the 2010–11 to 2018–19 California Healthy Kids Surveys. Multilevel logistic regressions indicated a stronger positive association between RML and co-use among non-Hispanic White youth (OR=1.21) relative to Hispanic (OR=1.02) or Black youth (OR=0.85). Among drinkers who had not consumed five or more drinks on any occasion in the past 30 days (non-heavy drinkers), the positive association between RML and co-use was stronger among American Indian/Alaska Native youth (OR=2.19) compared to non-Hispanic Whites (OR=1.56). For heavier drinkers it was stronger for Native Hawaiian/Pacific Islanders (OR=1.47). Among marijuana users, there was a stronger inverse association between RML and co-use among Black youth (OR=0.72) compared to non-Hispanic/Latino White youth (OR=0.84). RML may increase the risk of co-use to a greater extent among non-Hispanic White youth than other race/ethnic groups in California, but broadly increases the risk among youth who engage in alcohol use or heavy drinking.

Keywords: Adolescents, policy, marijuana, alcohol, co-use

Over the past decade, there has been significant liberalization of marijuana laws in the United States. As of July 2023, 24 states and the District of Columbia have legalized use of recreational marijuana use for adults aged 21 years of age and older (ProCon.org, 2023). In the state of California, adult recreational marijuana use was legalized in November 2016, and retail sales began in January 2018 (California Bureau of Cannabis Control, 2019). The liberalization of marijuana laws raises public health concerns, especially about possible consequences of marijuana legalization for adolescents’ marijuana use and associated physical and mental health outcomes (Hammond et al., 2020; National Academies of Sciences, Engineering, and Medicine, 2017; Volkow et al., 2014). Notably, marijuana and alcohol co-use may increase the risk for such outcomes beyond the use of either substance alone (Brière et al., 2011). Although some studies have found a positive association between recreational marijuana legalization (RML) and adolescents’ co-use of marijuana with alcohol, especially among drinkers (García-Ramírez et al., 2021; Paschall et al., 2021b), none have considered how this association might differ across racial and ethnic groups. To address this gap in the literature, this study investigated whether RML was associated with increased co-use of marijuana and alcohol by adolescents in California and if this association differed among racial and ethnic groups.

Co-use of marijuana and alcohol can refer to either concurrent use or simultaneous use. Concurrent use is the use of both substances, but not necessarily at the same time, whereas simultaneous use refers to the use of both substances close in time so that their effects overlap (Sokolovsky et al., 2020). In a study with high-school students, simultaneous use of alcohol and marijuana was associated with a two-fold increase in the likelihood of experiencing problems (e.g., legal, academic, health) in 11th grade after controlling for problem levels in 10th grade (Brière et al., 2011). A study using ecological momentary assessments with a community sample of adolescents found that each occasion of simultaneous use of alcohol and marijuana was associated with an increase in the number of problems reported (e.g., violence, driving under the influence, riding with a drunk driver) (Lipperman-Kreda et al., 2017). Another recent study of adolescents and young adults similarly found that simultaneous marijuana and alcohol use at a party, compared with alcohol only, was associated with experiencing more problems (e.g., hangover, punishment by their parents, risky sexual behaviors, experiencing sexual violence) (Egan et al., 2019). A review of epidemiologic, laboratory, and clinical research concluded that cannabis and alcohol co-use is associated with more frequent and intense use of these substances, and increased risk for cannabis and alcohol use disorders, mental health disorders, impaired driving, and other adverse behavioral and social consequences (Yurasek et al., 2017).

Given the liberalization of marijuana laws, it is important to understand whether RML is associated with increases in marijuana and alcohol co-use among adolescents. Although research findings are mixed, one study using statewide samples of adolescents in Oregon from 2010 to 2018 found a significant post-RML increase in past 30-day marijuana and alcohol co-use, particularly among adolescents living in counties with higher levels of retail marijuana and alcohol outlet density (García-Ramírez et al., 2021). Another study using statewide samples of adolescents in California from 2010–2019 found that RML was positively associated with co-use among adolescents, particularly among those who reported past 30-day alcohol use and heavy drinking, but was inversely associated with co-use among past 30-day marijuana users (Paschall et al., 2021b).

It is also possible that RML may differentially affect adolescents from different racial and ethnic groups, thus contributing to health disparities. Studies in California, Colorado, and Washington indicate that recreational marijuana outlets and medical marijuana dispensaries tend to be concentrated in neighborhoods with higher levels of poverty, crime, and racial/ethnic minority populations (Morrison et al., 2014; Shi et al., 2016; Tabb et al., 2018). Higher rates of marijuana use, and marijuana use disorder have been observed among minority youth in urban neighborhoods with higher levels of poverty, drug-related crime, and social disorder (Hasin et al., 2015). A study in Portland, Oregon found that a larger number of licensed cannabis stores were located in neighborhoods with higher levels of economic deprivation, suggesting there may be higher levels of exposure among racial/ethnic minority youth (Firth et al., 2020). In addition, to the extent that marijuana retail outlets are concentrated in economically disadvantaged neighborhoods with higher racial and ethnic minority populations, it is likely that minority adolescents are more exposed to marijuana marketing. Exposure to marijuana marketing has been associated with intent to use by adolescents (D’Amico et al., 2015, 2018; Hust et al., 2020; Palamar, 2014; Rose et al., 2019), and thus RML may have a greater impact on these youth.

More recently, a study monitoring the locations of licensed and unlicensed outlets in Los Angeles, found that most unlicensed outlets were in low-income areas with a predominantly Latinx population, whereas most licensed outlets were in areas with a majority White population (Firth et al., 2022). Thus, Latinx and African American youth in some locations may have greater exposure to cannabis stores and products that are not regulated, while White youth may have greater exposure to licensed retail outlets that are more likely to comply with age and marketing restrictions.

Although RML and decriminalization of cannabis possession and use may reduce social justice harms associated with discriminatory law enforcements practices (Carliner et al., 2017), legalization may differentially affect marijuana use and co-use with alcohol among adolescents in some racial/ethnic groups, potentially leading to or increasing disparities in health, social, and psychological harms. Thus, a previous study in California suggested that African American, American Indian/Alaska Native, Native Hawaiian/Pacific Islander, and multiracial students had greater odds of lifetime and past 30-day marijuana use compared to White students, though RML was more strongly related to marijuana use among White youth (Pape et al., 2009; Paschall et al., 2021a). However, little is known about whether this is also true for marijuana and alcohol co-use.

To address this question, this study examined associations of RML with marijuana and alcohol co-use among adolescents of different racial and ethnic backgrounds using data from the California Healthy Kids Survey (CHKS) from 2010–2011 through 2018–2019. We did not take state alcohol policies into consideration as they did not change significantly during the time period of this study (Blanchette, et al., 2020). The association between RML and co-use was examined for the total sample and for subgroups who engaged in past 30-day alcohol use, heavy drinking, and marijuana use. Because of the mixed findings regarding locations of licensed and unlicensed retail stores and marketing, we did not have directional hypotheses regarding racial/ethnic differences in the association of RML with marijuana and alcohol co-use. However, based on previous studies, we hypothesized that RML would be associated with increased co-use among adolescents who engaged in alcohol use or heavy drinking at least once per month, regardless of race/ethnicity.

Method

Study design and sample

California Healthy Kids Survey.

This study used successive annual cross-sectional survey data from 7th, 9th, and 11th grade students who participated in the California Healthy Kids Survey (CHKS) from 2010–2011 to 2018–2019. CHKS is the largest statewide self-administered survey of health-related behaviors and attitudes in the U.S. and has been administered every other year since 1998, with about half of the schools participating in alternate years (California Department of Education, 2019). CHKS is conducted by WestEd, a nonprofit research organization, in collaboration with the California Department of Education. School districts were formerly required to participate in CHKS to comply with the No Child Left Behind Act, Title IV, and are now required to participate if they receive funding under the State Tobacco Use Prevention Education Program (California Department of Education, 2019). Otherwise, CHKS participation is voluntary. About 75% of all California school districts currently participate in CHKS. Minimum CHKS requirements include participation of by 7th, 9th, and 11th graders, and at least a 60% response rate with either passive or active parental consent. Based on a review conducted by our study team with a random sample of high schools, response rates are typically 70% or greater for each participating school (Grube et al., 2021).

Study Sample.

Because of changes in the formatting of the questions about ethnicity and race in 2010–2011, this study is based on CHKS data for 2010–2011 to 2018–2019 school years from 3,330,912 students in 3,812 schools, 852 school districts, and all 58 counties in California. The study was deemed exempt by the Pacific Institute for Research and Evaluation IRB because it comprised secondary analyses of anonymous survey data.

Measures

Marijuana use.

From 2010−2011 to 2016−2017, students were asked: ‘During the past 30-days, on how many days did you use marijuana (pot, weed, grass, hash, bud)?’ With six response options including: 0 days, 1 day, 2 days, 3−9 days, 10−19 days, and 20−30 days. The question was modified in 2017−2018 and 2018−2019 to include smoke, vape, eat, or drink to reflect the increasing variety of cannabis products. Because the frequency distributions were highly skewed, these variables were dichotomized to represent any past 30-day marijuana use.

Alcohol use.

Students were provided with a definition of what was meant by an alcoholic drink and were asked: ‘During the past 30-days, on how many days did you have at least one drink of alcohol?’ Response options were: 0 days, 1 day, 2 days, 3−9 days, 10−19 days, and 20−30 days. They were also asked about heavy episodic drinking: ‘On how many days did you have five or more drinks of alcohol in a row, that is, within a couple of hours?’ with the same response options. Dichotomous variables were created to represent two mutually exclusive groups. Respondents who reported drinking in the past 30 days, but did not report heavy drinking were classified as nonheavy drinkers. Respondents were classified as heavy drinkers if they reported any heavy drinking in the past 30 days.

Marijuana and alcohol co-use.

Based on the responses to the questions about past 30-day alcohol and marijuana use, a dichotomous variable was created to represent any past 30-day marijuana and alcohol co-use (1 = yes, 0 = no). Because the survey did not determine whether co-use occurred at the same time, this variable reflects any concurrent or simultaneous use of alcohol and marijuana.

Demographic variables.

Students were asked to report their grade level and gender. In separate questions, students were asked to self-report their ethnicity (Hispanic or Latino) and race, by choosing one of the following options: American Indian or Alaska Native, Asian, Black or African American, Native Hawaiian or Pacific Islander, White, or more than one race (multiracial). We created an ‘unknown’ race category because a large percentage of students reported ethnicity, but not race. Hispanic/Latino was coded as a single dummy variable with non-Hispanic/Latino as the reference group. A series of dummy variables were created representing each racial category with non-Hispanic/Latino White as the reference group. All race groups included only non-Hispanic/Latino students. Grade was coded as two dummy variables representing 9th and 11th grades with 7th grade as the reference group. Self-reported sex was coded as female with male as the reference category. Survey year was coded 1–9 representing the school year when CHKS data were collected and was included in the analyses to account for the secular trend in marijuana and alcohol co-use.

Urban/rural context.

We used the U.S. Department of Agriculture Rural−Urban Continuum Code for each of the 58 California counties (U.S. Department of Agriculture, 2013) to represent the urban/rural context of school locations. These codes range from 1 (metropolitan areas with ≥1 million population) to 9 (completely rural or <2,500 urban population).

Legalization.

The pre-post RML variable was coded 0 for the 7 school years up to and including the school year when RML went into effect on November 9, 2016 (2010–2011 to 2016–2017) and coded 1 for the two full school years after RML (2017–2018 and 2018–2019). We were not able to disaggregate Fall 2016 from Spring 2017 CHKS data.

Statistical Analyses

Descriptive statistics were conducted for the total sample and three subgroups that reported past 30-day non-heavy alcohol use, heavy alcohol use, and marijuana use. A preliminary logistic regression analysis was conducted to examine unadjusted race/ethnic differences in co-use across the total sample. The primary analyses were multi-level logistic regression analyses to assess racial/ethnic differences in changes in past 30-day marijuana and alcohol co-use after RML for the total sample and the three marijuana and alcohol use subgroups, controlling for demographics, secular trend (school year), and urban/rural context. To investigate possible moderating effects of ethnicity/race, regression models included RML × ethnicity/race interaction terms, the main effects for RML and ethnicity/race dummy variables, and the covariates. Finally, to estimate the ORs and standard errors for RML associations with co-use for each of the race/ethnicity groups, a subsequent regression included all RML × ethnicity/race interaction terms, including RML × non-Hispanic/Latino Whites, and covariates, but not the overall pre/post RML dummy variable. Parallel models were used to explore race and ethnic differences in the associations of RML with co-use among non-heavy drinkers, heavy drinkers, and marijuana users. Analyses were conducted in HLM version 8.0 software to account for the non-independence of observations nested within schools and counties (Raudenbush et al., 2019). Sample weights were created by the study team based on the California Department of Education’s student population statistics by grade, gender, ethnicity and race, and were applied in all analyses (California Department of Education, 2021).

Results

Sample Characteristics

About eight percent of students in the total sample reported past 30-day marijuana and alcohol co-use over the study period, while 31.6% of non-heavy drinkers, 67.8% of heavy drinkers, and almost 70% of marijuana users reported past 30-day co-use (Table 1). Over the nine-year period, 8.2% of non-Hispanic/Latino White students reported any past 30-day co-use, compared to 9.1% of Hispanic/Latino, 12.4% of American Indian/Alaska Native (AIAN), 8.9% of Black, 2.6% of Asian, 7.4% of Native Hawaiian/Pacific Islander (NHPI), 7.7% of multiracial, and 7.5% of unknown race students. Results of logistic regression analysis (unadjusted odds ratios) indicated that Hispanic/Latino (OR = 1.14, 95% CI = 1.11, 1.18), Black (OR = 1.10, 95% CI = 1.01, 1.20), and AIAN (OR = 1.44, 95% CI = 1.37, 1.53) students were significantly more likely to report co-use than non-Hispanic/Latino Whites. Asian students were significantly less likely to report co-use than non-Hispanic/Latino Whites (OR=0.35, 95% CI=0.32, 0.38).

Table 1.

Sample characteristics, percent

Variable Total Sample (N=3,319,329) Non-heavy drinkers (n=251,835)a Heavy drinkers (n=281,938)a Marijuana Users (n=386,116)a
Past 30-day alcohol and marijuana co-use 8.1 31.6 67.8 69.7
Past 30-day non-heavy drinking 7.5 - - 20.4
Past 30-day heavy drinking 8.4 - - 49.3
Past 30-day marijuana use 11.6 31.6 67.8 -
Grade 7 34.0 19.7 11.0 12.1
Grade 9 34.9 37.0 33.4 36.2
Grade 11 31.1 43.3 55.6 51.7
Female 48.5 56.4 46.5 45.1
Ethnicity
Hispanic/Latino 52.8 60.2 58.6 59.5
Raceb
American Indian/ Alaska Native 0.6 0.6 1.0 0.9
Asian 11.7 5.6 4.1 3.9
Black 6.2 5.2 5.3 7.9
Native Hawaiian/ Pacific Islander 0.5 0.4 0.5 0.5
White 25.0 24.9 27.6 24.1
Multiracial 2.6 2.4 2.3 2.6
Unknown race 0.7 0.6 0.7 0.7
Urban/rural context
 Metro
≥ 1 million population 71.7 69.5 67.9 68.6
≥ 250K – 1M population 21.9 23.0 23.2 23.5
< 250K – 20K population 3.7 4.2 4.8 4.2
 Nonmetro
≥ 20K population 1.3 1.7 2.2 1.9
<20K population 1.3 1.5 2.0 1.7
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Note: Percentages are weighted whereas sample (N) and subsample (n) sizes are unweighted.

a

The two subgroups of past-30-day drinkers are mutually exclusive, but these subgroups overlap with past-30-day marijuana users.

b

Race groups are non-Hispanic/Latino.

Multi-level Regression Analyses

Moderating Effects of Ethnicity/Race.

Overall, RML had a positive association with co-use for the total sample (OR = 1.21, 95% CI = 1.17, 1.26), heavy drinkers (OR = 1.22, 95% CI = 1.14, 1.31), and non-heavy drinkers (OR = 1.56, 95% CI = 1.45, 1.67), but an inverse association for marijuana users (OR = 0.84, 95% CI = 0.78, 0.89). A summary of the results to assess moderating effects of ethnicity/race on these associations between RML and co-use are presented in Table 2, while results of subsequent analyses examining the associations between RML and past 30-day marijuana and alcohol co-use for each racial/ethnic group are reported in Table 3. For the total sample, there was an inverse significant moderating effect of Hispanic/Latino ethnicity, Black, multiracial, and unknown race groups on the association between RML and co-use as shown by the significant interaction terms in Table 2. Among non-heavy drinkers, there were positive significant moderating effects for American Indian/Alaska Native (AIAN), but an inverse significant moderating effect for Asian, and Black students on the association between RML and co-use relationship. Among heavy drinkers, there was a positive significant moderating effect on the association between RML and co-use relationship for Native Hawaiian/Pacific Islander (NHPI) students relative to non-Hispanic/Latino Whites. Finally, among marijuana users, there was a negative significant moderating effect for NHPI, Black, and a positive significant moderating effect for Hispanic/Latino and unknown race groups on the association between RML and co-use.

Table 2.

Summary results of multi-level regression analyses of moderating effects of ethnicity/race group on the association between RML and past 30-day alcohol and marijuana co-use, odds ratio (95% confidence interval)a

Predictors Total sample (N=3,319,329) Non-heavy drinkers (n=251,835)b Heavy drinkers (n=281,938)b Marijuana users (n=386,116)b
RML 1.21 (1.17, 1.26)** 1.56 (1.45, 1.67)** 1.22 (1.14, 1.31)** 0.84 (0.78, 0.89)**
RML × Hispanic/Latino 0.84 (0.80, 0.88)** 1.01 (0.95, 1.09) 1.03 (0.96, 1.11) 0.89 (0.85, 0.94)**
RML × AIAN 0.96 (0.86, 1.07) 1.40 (1.07, 1.84)** 1.32 (0.98, 1.77) 1.03 (0.85, 1.24)
RML × NHPI 0.93 (0.87, 1.01) 0.99 (0.80, 1.24) 1.20 (1.03, 1.40)* 0.88 (0.79, 0.99)*
RML × Asian 0.98 (0.94, 1.02) 0.91 (0.84, 0.99)* 0.99 (0.88, 1.12) 1.05 (0.97, 1.13)
RML × Black 0.69 (0.64, 0.75)** 0.83 (0.72, 0.96)* 1.05 (0.89, 1.12) 0.86 (0.79, 0.93)**
RML × Multiracial 0.90 (0.86, 0.95)** 0.97 (0.92, 1.03) 0.99 (0.88, 1.11) 0.97 (0.91, 1.04)
RML × Unknown 0.76 (0.68, 0.85)** 1.33 (0.94, 1.88) 1.27 (0.72, 2.21) 1.25 (1.00, 1.57)*
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a

Regression models included students’ gender, ethnicity, race (excluding non-Hispanic/Latino White, the referent group), grade level, school year, county urban/rural classification, a pre-post RML dummy variable, pre-post RML × ethnicity and race interaction terms.

b

The two subgroups of past 30-day drinkers are mutually exclusive, but these subgroups overlap with past 30-day marijuana users.

*

p < .05

**

p < .01

Table 3.

Estimates of associations between RML and past 30-day alcohol and marijuana co-use by ethnic/race group, odds ratio (95% confidence interval)a

Ethnicity/Race Total sample (N=3,319,329) Non-heavy drinkers (n=251,835)b Heavy drinkers (n=281,938)b Marijuana users (n=386,116)b
Hispanic/Latino 1.02 (0.99, 1.05) 1.58 (1.48, 1.69)** 1.26 (1.21, 1.32)** 0.75 (0.70, 0.80) **
AIAN 1.17 (1.06, 1.28)** 2.19 (1.67, 2.87) ** 1.61 (1.22, 2.14)** 0.86 (0.71, 1.04)
NHPI 1.13 (1.06, 1.22)** 1.55 (1.23, 1.95)** 1.47 (1.25, 1.73) ** 0.74 (0.67, 0.81)**
Asian 1.19 (1.15, 1.23)** 1.42 (1.31, 1.54) ** 1.21 (1.09, 1.35)** 0.87 (0.79, 0.97)*
Black 0.85 (0.79, 0.90) ** 1.30 (1.15, 1.46) ** 1.29 (1.09, 1.53)** 0.72 (0.66, 0.78) **
White 1.21 (1.17, 1.26)** 1.56 (1.45, 1.67)** 1.22 (1.14, 1.31)** 0.84 (0.78, 0.89)**
Multiracial 1.09 (1.05, 1.14) ** 1.52 (1.41, 1.63)** 1.21 (1.06, 1.37)** 0.81 (0.75, 0.88)**
Unknown race 0.92 (0.82, 1.04) 2.08 (1.47, 2.93)** 1.55 (0.91, 2.65) 1.05 (0.85, 1.30)
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a

Models included students’ gender, ethnicity, race, grade level, school year, county urban/rural classification, and pre-post RML × ethnicity and race interaction terms, including pre-post RML × White but not the pre-post RML dummy variable, in order to obtain estimates of and significance tests for the associations of RML with co-use for each ethnic/race group.

b

Past 30-day non-heavy and heavy drinkers are mutually exclusive, but these subgroups overlap with past 30-day marijuana users.

Note: Boldface estimates are significantly different from those for non-Hispanic/Latino Whites (p < .05).

*

p < .05

**

p < .01 (p values indicate significant RML effects for specific ethnic/race groups).

Associations of RML with Co-Use by Ethnic/Race Group.

Results of subsequent analyses for the total sample (Table 3) indicated that there was a significant 21% post-RML increase in the odds of past 30-day co-use among non-Hispanic/Latino White students, a nine percent post-RML increase in the odds of co-use among multiracial students, and a 19% post-RML increase among Asian students. In contrast, there was a significant 15% post-RML decrease in the odds of past 30-day co-use among Black students, and no association between RML and co-use among Hispanic/Latino students and students of unknown race. Among non-heavy drinkers, there were significant post-RML increases in the odds of co-use for all racial/ethnic groups with ORs ranging from 1.30 for Black students to 2.19 for AIAN students. The association between RML and co-use for AIAN, Asian and Black students was significantly different from the association for non-Hispanic/Latino White students. Among heavy drinkers, there were significant post-RML increases in the odds of co-use for all racial/ethnic groups except unknown race with ORs ranging from 1.21 for Asian and multiracial students to 1.61 for AIAN students. The association between RML and increased co-use for NHPI students who were heavy drinkers was significantly stronger than for non-Hispanic/Latino White students. For marijuana users the odds of past 30-day co-use decreased significantly for almost all racial/ethnic groups after RML except for AIAN students and those with unknown race, with ORs ranging from 0.72 for Black students to 0.87 for Asian students. Additionally, the negative associations between RML and co-use for marijuana users who were Hispanic/Latino, Black, and unknown race were significantly stronger than that for non-Hispanic/Latino White students.

Discussion

We found that among adolescents in California, RML was less strongly associated with increases in past 30-day marijuana and alcohol co-use among adolescents of Hispanic/Latino ethnicity and Black, multiracial, and unknown race compared to non-Hispanic/Latino Whites. The positive associations between RML and co-use among adolescents in the other three racial groups (Asian, AIAN, NHPI) were statistically equivalent to that observed for non-Hispanic/Latino White students. To some extent, these racial and ethnic differences in the association between RML and co-use may reflect the greater increases in marijuana use following RML among White youth observed in a previous study of California adolescents (Paschall et al., 2021b). However, racial/ethnic differences in the association between RML and co-use may also reflect differences in marijuana and alcohol availability from social and commercial sources and beliefs related to norms and risks related to use and co-use of these substances, though further research is needed to better understand these differences.

In the subsamples of drinkers and marijuana users, there were also some racial/ethnic differences in the strength of association between RML and co-use, though the direction of these relationships was generally the same across all racial/ethnic groups. Consistent with our hypothesis, RML was positively associated with co-use among non-heavy and heavy drinkers regardless of ethnicity/race, suggesting an increase in complementary use of alcohol and marijuana after RML. In contrast, there was a decrease in co-use in the subsample of marijuana users across almost all racial/ethnic groups, with one exception, unknown race. Some research suggests that youth may reduce alcohol use in more liberal cannabis environments, (Bailey et al., 2020) and our results indicate that this was the case for recent marijuana users, suggesting substitution of cannabis for alcohol in this subgroup.

Limitations

This study has some limitations. First, although the sample size is large, the CHKS sample of 7th, 9th, and 11th graders may not be representative of all adolescents in California or other states where RML has been implemented. Responses to survey questions about alcohol and marijuana use may be subject to social desirability and recall errors, and missingness on the survey questions may have introduced bias. Because of the lack of specificity regarding the timing of marijuana and alcohol use in survey questions, simultaneous use and concurrent co-use could not be distinguished. It is important to note that the survey design (successive cross-sections) precludes making conclusions regarding within-person changes in these behaviors. In addition, the lack of a control or comparison group and controls for other historical changes not considered in this study may limit our conclusions regarding the association between RML and alcohol and marijuana co-use.

Conclusion

This study provides evidence that the association between RML and marijuana and alcohol co-use varies across California adolescents in different racial and ethnic groups. Further research is needed to better understand the extent to which local regulatory policies and retail availability of marijuana and alcohol may contribute to co-use among underage youth in different racial and ethnic groups. The legalization of recreational marijuana may increase the risk of marijuana and alcohol co-use for some racial/ethnic groups among California adolescents, and more so for youth who engage in alcohol use or heavy drinking.

Given the observed differences in the relationship between RML and co-use across racial and ethnic groups, different prevention approaches may be appropriate for different communities. Further research on state and local regulatory policies and retail availability of alcohol and marijuana should be conducted to better understand racial/ethnic differences in possible effects of RML across communities. Future studies should focus on specific race and ethnic groups to test group-specific hypotheses.

Acknowledgment.

This work was supported by the National Institute on Alcohol Abuse and Alcoholism (NIAAA) of the U.S. National Institutes of Health (NIH) P60-AA006282 and T32-AA014125. The content is solely the responsibility of the authors and may not represent the views of NIAAA or NIH.

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