This is the first study to simultaneously examine the density of both MCDs and RCRs around young adults’ homes and associations with future intentions to use cannabis, including the co-use of cannabis with tobacco/nicotine. Our results suggest that young adults who lived in an area with a greater density of any type of outlet were not significantly more likely to report stronger intentions to use cannabis, e-cigarettes, or cannabis mixed with tobacco/nicotine in the future. One prior study found that associations between legalization and more positive attitudes towards cannabis were stronger among those who had previously used tobacco (Cohn et al. 2016). Similarly, data from a Monitoring the Future study found higher odds of intending to use cannabis were associated with recreational legalization among adolescents already at high risk for use, including cigarette smokers (Palamar et al. 2014). Thus, future research in a larger sample could examine whether the increasing density of RCRs and MCDs may be associated with greater intentions to use cannabis among those who previously used tobacco/nicotine or cannabis.

We found several interesting differences by race/ethnicity that may have important implications for understanding disparities in cannabis use. For example, only white young adults who lived near a higher density of any outlets tended to report stronger intentions to co-use cannabis with tobacco/nicotine. Associations between the density of outlets and co-use intentions among white young adults appear to be driven mostly by access to recreational cannabis, suggesting that the effects of RCRs may be stronger than MCDs and that the emergence of RCRs in L.A. County, which made cannabis legally available to everyone over the age of 21 regardless of medical conditions, appears to be especially influential for white young adults. Among Asian young adults, increasing MCD density appears to be somewhat influential for intentions to use cannabis mixed with tobacco/nicotine. It is unclear why MCDs are influential for Asian young adults whereas any type of outlet, but especially RCRs, are influential for co-use intentions among white young adults. One prior study reported no difference in medical marijuana card ownership by race (Tucker et al. 2019a). Thus, white and Asian young adults may have a greater awareness of RCRs and MCDs, respectively, in their neighborhoods. Since both racial groups experienced significant or marginal associations with intentions to co-use, it is worth noting that co-use is associated with more frequent and problematic use, poorer mental and physical health, and delinquent behaviors (Akbar et al. 2019; Cobb et al. 2018; Hernandez-Serrano et al. 2018; Tucker et al. 2019b) compared to single-product use. Moreover, co-use may incur greater health risks compared to the use of single products such as respiratory problems (Layden et al. 2019; Centers for Disease Control and Prevention 2019), although the long-term health effects of vaping co-use are unknown.

Results also indicated that Hispanic young adults who lived near more MCDs reported weaker intentions to use e-cigarettes, but not necessarily cannabis or cannabis mixed with tobacco/nicotine. The inverse association of MCD density with intentions to use e-cigarettes was not expected, and it is unclear why this might have emerged among Hispanic young adults only. Further research is needed to determine whether this is a robust finding and, if so, to understand the impact of MCD exposure on e-cigarette use in Hispanic young adults.

Taken together, these findings could shed light on the density of RCRs as a contextual risk factor for higher rates of co-use among white young adults and suggest that implementation of targeted intervention efforts among residents who live near more RCRs may be an efficient way to curb cannabis use and co-use of cannabis mixed with tobacco/nicotine, especially among white young adults. It is important to note, however, that black, Hispanic, and Asian youths report more negative consequences such as problems with physical health and poor academic functioning when using cannabis and nicotine/tobacco at the same levels of non-Hispanic white youth (D’Amico et al. 2016a, b; Dunbar et al. 2018; Tucker et al. 2019c). Therefore, even though outlet density does not appear to increase intentions to use among Hispanic young adults, they may still be at risk for poorer outcomes even when using at the same levels as white youth. This may be particularly true for Asian young adults who showed a higher risk of intentions to use e-cigarettes associated with MCD dispensary compared to white young adults.

Findings should be considered in the context of limitations. First, we could not examine the density of specialty vape shops or tobacco outlets. There are no publicly searchable databases of specialty vape shops, and tobacco outlet data do not indicate whether shops sell e-cigarettes or vaping products. Moreover, tobacco outlet data do not include single-owner establishments because of privacy concerns, which undercounts the availability of tobacco shops and, therefore, the availability of e-cigarettes or vaping products. Second, the results may not generalize to populations outside of L.A. County. Lastly, the relatively small number of Black young adults in the sample necessitated including them in the other/multi-racial group, which precluded an examination of differences between MCD and RCR density for black young adults.

In summary, there is evidence from this study that non-Hispanic white and, to a lesser extent, Asian young adults who live near a higher density of cannabis outlets are more likely to report stronger intentions to co-use cannabis with tobacco/nicotine over the next 6 months. Future research could use real-time data captured by methods such as ecological momentary assessments to more precisely determine how youths navigate their environments to travel to and purchase from recreational retailers, how cannabis and e-cigarette advertising may affect co-use intentions, and whether policies that seek to restrict geographic locations and density of recreational retailers could potentially reduce harmful levels of cannabis use and co-use with tobacco/nicotine. These restrictions could modify the risk for negative consequences especially among racial/ethnic subgroups who may be more likely to be influenced by their local cannabis retail environments.