However, most published studies have focused only on adolescents under the age of 18 years and do not reflect the adult population to which medical marijuana policies apply . Therefore, long-term longitudinal studies are needed to monitor the effects of marijuana legalization, marijuana initiation/ re-initiation, cigarette initiation/ reinitiation, and patterns of co-use across all age categories. Additionally, it is recommended that such studies take into account statewide variables including number of years since the policy went into effect to adequately capture any measurable changes. These data are needed to explore the growing evidence and public health concerns about the potential “gateway” effect of marijuana on cigarette initiation and nicotine dependence in adolescents and young adults in addition to the potential for re-initiation of cigarettes among former tobacco users. As more states pass marijuana policies, potential increases in co-use could have important treatment implications. Cigarette smokers who also reported current marijuana use were more likely to have nicotine dependence,commercial greenhouse benches which is a known predictor of smoking and quitting behavior . The positive link between co-use and nicotine dependence was observed across age categories but these associations differed across measures of dependence . We analyzed both NDSS and TTFC. NDSS scores might have been a better measure of nicotine dependence in our comparison across age groups since the scale addresses five aspects of dependence .
In comparison, the TTFC single-item scores might not have captured dependency, particularly in adolescent and young adult populations, who have yet to become regular and established smokers. Other studies have shown problems in using TTFC as a measure of dependence in young adults . Since our analysis included both adolescents and adults, we report both NDSS and TTFC measures of nicotine dependence. In addition, in the present study, cigarette smokers who reported ever but not current marijuana use were at greater risk of having nicotine dependence compared to never marijuana users. This finding supports that the effect of THC exposure on nicotine receptors may be irreversible . Studies are needed to further examine both short term and possibly even the long-term effects of THC and nicotine exposure on nicotine dependence and tobacco cessation. In this analysis, 12–17 year old adolescent and 50–64 year old cigarette and marijuana cousers had the highest odds of having nicotine dependence. These findings support previous studies linking co-use and nicotine dependence in adolescents and young adults and add to preliminary data that this association was also stable in adults and, surprisingly, particularly robust in 50–64 year old adults. These findings reflect evidence of a U-shaped effect between age and nicotine dependence which peaks at age 50 years due to changes in nicotinic receptors and nicotine-associated metabolism with age , and suggest that this relationship was stable among co-users. Studies are needed to determine the extent to which THC exposure and/or current marijuana use add to this effect . Additionally, 50–64 year olds may represent a unique birth cohort who spent their formative years during the 1960’s and 1970’s with minimal tobacco regulations coupled with a counterculture that promoted marijuana use among a large population . More studies on the Baby Boomer generation, specifically, their perceptions about marijuana, current marijuana use including purpose of use , modality, cigarette co-use, and health outcomes could provide a glimpse into the future as continued legalization will likely influence social norms across the general population .
As more states adopt liberal marijuana policies, more studies are needed to understand co-use including the relationship between THC and nicotine in addition to other individual-level factors such as genetics and personality traits that might influence dependence and cessation . We found higher percentages of non-Hispanic Whites and Blacks/ African-Americans in states where medical marijuana was illegal. In this study, these results may be attenuated since our analysis comparing nicotine dependence depended on exclusion of blunt use. The American Civil Liberties Union report data from the NSDUH and Uniform Crime Reporting Data showing that Black males were no more likely to report marijuana use, but 4-times more likely to be incarcerated for marijuana possession compared to their non-Hispanic White male counterparts . Epidemiologic data have shown a linear increase in cigarette and marijuana co-use in Whites, Blacks/ African-Americans, and Hispanics with the fastest rate of increase among Blacks/ African-Americans . Among Blacks/ African-Americans, it is possible that statewide legalization of medical marijuana could help to reduce marijuana-related incarcerations, and at the same time, influence the rate of couse. We are cognizant of the many layers that add to the complexities around the issue of marijuana legalization that are well beyond the scope of our study. We recommend future research will assess potential and actual benefits/ costs of marijuana legalization to society at large, and in states where marijuana is legal, identify issues that can be addressed with specific regulatory measures .Study limitations include the cross sectional nature of these analyses which limits our ability to infer causality. Interpretation of our findings is limited to cigarette smokers which is distinct from those who reported other tobacco products . We were unable to examine statewide legalization of medical marijuana by the number of years the policy went into effect using the NSDUH to account for time lags from adoption to full implementation. The NSDUH public dataset only provides a binary categorization of states that were legal vs. illegal that lumps states that just passed the law with long-term legalization states limits our ability to detect long-term effects and may have attenuated our findings. Further study is needed to examine the effect of combusted vs. non-combusted marijuana use on nicotine given increasing prevalence of edible and aerosolized delivery of marijuana with vaporizers .
At present, the NSDUH does not ask respondents to indicate whether use was combusted and/ or non-combusted and we recommend that future surveys collect information on marijuana modality to elucidate the relationship between various forms of marijuana intake and nicotine and/ or THC dependence. Data on combusted vs. non-combusted THC intake can also help to identify if there might be differences in health effects across marijuana use modality. In addition, the present study did not examine population density which might be a potential covariate for marijuana use. Strengths of the study were use of a large national dataset representative of the U.S. population and internal validity of nicotine dependence comparisons across age categories using the same dataset,grow bench which eliminates methodological variations from one study to another. Medical marijuana legalization was positively associated with cigarette and marijuana couse and co-users were at greater risk for nicotine dependence. Long-term longitudinal data across age groups are needed to elucidate these results. In the meantime, it is recommended that stakeholders in tobacco control participate in policy discussions involving marijuana legalization including regulatory measures to prevent further co-use and develop novel cessation treatments to help co-users who may have a harder time with quitting. Marijuana use is legal for medical or recreational purposes in 33 states and Washington, DC . Recreational legalization has ushered in rapid commercialization . Both Colorado and Washington—the first 2 states to legalize marijuana for recreational use—have seen retail sales exceed a billion dollars annually . States with recreational marijuana have been inundated with mass marketing promoting marijuana use, and also an increase in novel marijuana products with tetrahydrocannabinol content at concentrations not evaluated for safety in humans . Given the absence of federal regulations in managing the commercial marijuana market, individual states are developing regulations governing marijuana advertising, production, and sale . In US adults, rates of recreational marijuana use and cannabis use disorders have increased considerably over the last several years .Legalization for medical purposes has been accompanied with increased daily use and marijuana use disorders among US adults . Approximately 15% of the US adult population used marijuana in some form in 2017 . Between 2016 and 2017, past-month use of marijuana increased nearly 2% among adults aged 18 to 25 years and 1.2% among adults 26 years and older . Additionally, national surveys suggest the perception of ‘‘great risk’’ from weekly marijuana use dropped from 50.4% in 2002 to 33.3% in 2014 and has dropped further since . Recent national surveys also demonstrate that the public attributes benefits to marijuana that are not supported by existing scientific evidence, such as relief from anxiety, stress, and depression, improved appetite, and improved sleep . It is unknown whether adult residents of states where marijuana has been commercialized for recreational use are more likely to attribute benefits to marijuana use.
Given the growing body of evidence that adverse consequences are associated with regular marijuana use , determining whether residents of recreational states perceive marijuana use differently than residents of states without commercial legalization is an important consideration and may inform the needs for more investment in communications of potential risks to the public. In this study, we examine the differences in beliefs about marijuana use and rates of use across states defined by their marijuana legalization status .Survey questions were developed by identifying gaps in existing federally funded national surveys, including the National Survey on Drug Use and Health and Monitoring the Future , and drafting questions to address those gaps. Questions were refined through interviews with marijuana industry professionals, dispensary staff, marijuana distributors, and mental health and substance use disorder experts. Survey items developed included individual opinions on the risks and benefits of marijuana use, comparisons of risks and benefits of marijuana to other psychoactive substances, and the form, amount, and frequency with which individuals use marijuana. In total, the survey included 29 questions assessing beliefs about the risks and benefits of marijuana and 54 questions assessing marijuana use. Answer options for all opinion questions used Likert scales to allow participants to respond with the answer most closely aligned with their beliefs. All questions were written at an 8th-grade reading level and were tested on a convenience sample of 40 adults to ensure readability and construct validity. Full details on survey development have been previously published . The survey tool is available in the supplementary material .We conducted a survey of a nationally representative sample of 16,280 US adults on risks and benefits of marijuana use. The survey was conducted using Knowledge Panel —a nationally representative panel of civilian, non-institutionalized US adults aged 18 years and older that has been used to survey public opinion since 1999 . The address-based sampling covers 97% of the country and encompasses a statistical representation of the US population. Households without internet access are provided with an Internet connection and a tablet to ensure participation. All participants in the panel are sampled with a known probability of selection. No one can volunteer to participate. Participants are provided with no more than 6 surveys a month and are expected to complete an average of four surveys a month . Sampling was stratified by legalization status of marijuana in the state of residence . California residents and young adults aged 18 to 26 years old were over sampled to facilitate a future investigation into the role of recreational legalization on use patterns among young adults in California. Sampling weights were provided by GfK.The response rate, determined using methods outlined by the American Association for Public Opinion Research, was the ratio of respondents to all potential participants . Characteristics of the survey respondents were weighted using weights provided by GfK to approximate the US population based on age, sex, race, ethnicity, education, household income, home ownership, and metropolitan area. All analyses used weighting commands using the weight variable provided by GfK to generate national estimates. We first compared the sociodemographic characteristics of our respondents to that of the NSDUH—an annual, federally funded epidemiologic survey . We then compared views and forms of marijuana use of residents across recreational, medical, and nonlegal states using chi-square statistics. Finally, we reported the prevalence of different forms of use stratified by legalization status of states and the associated 95% confidence interval . In supplementary analyses, using logistic regression, we examined views of residents of recreational states compared with other states after adjusting for baseline demographic characteristics including age, sex, race, employment status, and household size.