Adolescents that reported higher than average exposure to MM ads also tended to report greater marijuana use, stronger intentions to use marijuana in the future, stronger positive expectancies about marijuana use, and more negative consequences from use. In addition, adolescents who reported increased exposure to MM ads over the seven-year period also reported increases in their marijuana use, intentions to use, positive expectancies, and negative consequences. This association was particularly strong for exposure to MM ads and marijuana use. Overall, results suggest that exposure to MM advertising may not only play a significant role in shaping attitudes about marijuana, but may also contribute to increased marijuana use and related negative consequences throughout adolescence. The association between exposure to MM ads and past year consequences likely occurred because youth who were exposed to MM ads were then more likely to use marijuana more heavily and therefore experience more negative consequences. Future work should begin to explore mechanisms for these associations. Overall, our findings mirror those from the alcohol and tobacco fields, which have shown that increased exposure to advertising for these products is associated with increased use among adolescents . This highlights the importance of beginning to think about regulations for marijuana advertising , similar to regulations that are in place for tobacco and alcohol . Findings must be understood in the context of the changing legal landscape of marijuana in the United States. For example, it is important to note that marijuana use and consequences may be viewed differently than alcohol use and consequences,trimming cannabis as teens tend to associate marijuana use with fewer negative consequences than alcohol use .
For example, nearly one in five teens report driving under the influence of marijuana, one third of whom believed their driving ability was improved after marijuana use , and younger drivers are especially likely to believe that driving under the influence of marijuana is socially acceptable and safe . Given the health claims that are made for marijuana use , and the effects of advertising we found over this seven-year period, it is crucial to address perceptions about marijuana effects and the potential consequences from use as part of our prevention and intervention efforts with adolescents. One recent study found, for example, that when adults communicated with youth about information in anti-marijuana ads using moderate, non-directive language, this was more effective in decreasing adolescents’ intentions to use marijuana than when adults used more extreme, directive language . Teachers, parents, and community leaders need to be ready to provide teens with up-to-date information on both medical and recreational marijuana to help youth better understand that although there may be some benefits medically for adults , marijuana use during adolescence can affect functioning during the teen years as the brain is still developing , and is also associated with impairment in young adulthood and adulthood . Findings from this study are an important first step in understanding the long-term effects of MM advertising; however, there are limitations to our work. As the data indicated, there is a great degree of variability in exposure to MM ads, use, cognitions, and consequences, which is likely due to the fact that other factors are associated with these constructs, such as parental monitoring, peer use, or where an adolescent may live. Future work could begin to examine how these factors, along with advertising, may affect these associations over time. In addition, we cannot draw conclusions from this study about the reciprocal associations of exposure to MM ads with marijuana use and related cognitions.
Our previous longitudinal work examined these associations using cross-lagged analyses over one year and found a reciprocal association such that teens exposed to MM ads reported greater marijuana use, and teens who reported greater marijuana use were also more likely to report exposure to MM ads . In this study, we were more interested in capturing interindividual differences in intra-individual growth, as well as modeling the functional form of growth. The parallel process LGMs used in current analyses allow us to do that by focusing on conjoint longitudinal change in MM advertising and adolescents’ marijuana use, intentions, positive expectancies and negative consequences. It is also important to note that we only had one item measuring exposure to MM advertising. Future work could ask more detailed questions about where exposure to ads occurred to rule out recall bias. Another limitation is that we relied exclusively on self-reported marijuana use. However, the limits of self-report are often exaggerated , and recent work with young adults 18–21 has shown that self-reported alcohol use can be corroborated by biomarkers . In addition, our sample’s marijuana use rates match those seen for national samples . Finally, this sample was limited geographically to adolescents living in southern California, thus, generalizability may be restricted. Marijuana is one of the most commonly used psychoactive substances in the US, with an estimated 49% of adults having ever used marijuana, including 19% within the past year, and 12% within the past month. The prevalence of marijuana use has risen over the past several decades and its use is expected to increase as more states legalize marijuana. Medically, marijuana may help treat chemotherapy induced nausea and vomiting, chronic neuropathic pain, inflammatory conditions, Parkinson’s disease symptoms, and epilepsy. Despite these therapeutic benefits, marijuana use may have adverse effects on health including short-term and long-term use. Additionally, marijuana use has been associated with increased risk of psychiatric disorders.
Due to the expected rise in use coinciding with legalization, studies investigating the association between marijuana use and molecular or epigenetic mechanisms may provide novel insights into the short- and long-term impacts of marijuana on health-related outcomes. DNA methylation, one of the most-studied epigenetic modifications, is a regulatory process that affects gene expression through the addition or removal of methyl groups. These modifications can be induced by environmental and lifestyle factors, which may serve as blood-based biomarkers for recent and cumulative exposures. Additionally, the modifiable nature of DNA methylation allows for the investigation of exposure-induced changes to the epigenome and its variability across time, potentially leading to the identification of dynamic and/or stable biomarkers.These methylation changes may serve as biomarkers for recent and cumulative marijuana use, and subsequently,drying and curing cannabis may further our understanding of the acute and additive influences of marijuana on molecular and biological processes influencing downstream health conditions. Despite the growing use of marijuana, a limited number of studies have examined epigenome wide biomarkers associated with marijuana use. Previous studies have identified differentially methylated DNA signatures associated with marijuana, including markers located in AHRR, ALPG, CEMIP, and MYO1G. These biomarkers, however, were limited to a single time point and did not examine both recent and cumulative marijuana use. Studies examining the relationship between recent and cumulative marijuana use and epigenetic factors in a diverse population across time with repeated measurements may provide novel insights. Therefore, the purpose of this study was to investigate the association between recent and cumulative marijuana use and repeated genome-wide DNA methylation patterns measured in middle aged adults.Details of blood sample collection and DNA processing have previously been described. Briefly, a random sample of 1200 participants with available whole blood at both Y15 and Y20 underwent DNA methylation profiling using the Illumina MethylationEPIC BeadChip. Data process and quality control of the DNA methylation datasets were performed using the default settings in the R package Enmix. Low quality methylation measurements were defined as markers with a detection P < 1E−06 or less than 3 beads. A total of 6209 markers with a detection rate <95% and 87 samples with methylation measurements of low-quality >5% or extremely low intensity of bisulfite conversion probes were removed from further analysis. Additionally, 95 samples were identified as extreme outliers as determined by the average total intensity value [intensity of unmethylated signals + intensity of methylated signals ] or β value [M/] across all markers and Tukey’s method. Model-based correction was applied using ENmix and dye bias correction was conducted using RELIC . M or U intensities for Infinium I or II probes underwent quantile normalization separately, respectively. Low-quality methylation markers and β value outliers, as defined by Tukey’s method, were set to missing. After applying these criteria, 1042 and 957 samples at Y15 and Y20 remained for downstream analysis, respectively.In this multiple time point epigenome-wide association study of middle-aged adults, we observed 201 methylation markers associated with recent and cumulative marijuana use across time. We replicated 8 previously reported methylation markers associated with marijuana use.
We also observed 638 cis-meQTLs associated with several marijuana-methylation markers, as well as 198 differentially methylated regions. During pathway and disease analyses, marijuana-associated genes were statistically over represented in numerous pathways and diseases. While replication of these findings in independent cohorts is warranted, our results provide novel insights into the association between recent and cumulative marijuana use and the epigenome and related biological processes, which may serve as a mechanism of earlystage disease associated with marijuana use.Of these, cg05575921 in AHRR was associated with recent and cumulative marijuana use at both time points, including the single most-associated methylation marker for two of the four analyses. This methylation marker has previously been associated with heavy cannabis use among tobacco users, tobacco use, and is 1 of 172 CpGs included in the estimation of a DNA methylation surrogate for pack-years of smoking for GrimAge, a measure of biological age associated with lifespan. The association of this epigenetic marker with both tobacco and marijuana use may suggest common modulating effects on DNA methylation and may represent a nondiscriminatory smoke related biomarker, irrespective of tobacco or marijuana use. Additionally, cg05575921 has been associated with psychiatric disorders.The top methylation marker associated with recent marijuana use at Y15, cg18110140, is located on chromosome 15 in an ‘open sea’ region of the epigenome. This marker was recently found to be associated with smoking status. Several top epigenomic loci have also previously been associated with tobacco smoking, including BMF and MYO1B, and may provide additional measurable biomarkers for tobacco and marijuana exposure. Moreover, numerous epigenomic loci have been reported to have potential therapeutic benefits via the endocannabinoid system. NOX4 is a member of the NADPH oxidase family and an enzyme that synthesizes reactive oxygen species and cannabidiol , one of the most common cannabinoids, has been reported to attenuate ROS formation and enhance expression of NOX4. Similarly, TFEB is associated with the autophagy-lysosomal pathway and may aid in reducing inflammation and cognitive impairment via the cannabinoid receptor type II . Although the effect estimates for the observed associations are relatively small, the magnitude of the beta coefficients are consistent with previous EWAS studies and further studies investigating the cumulative effect of these individual CpGs may yield greater biological, and potentially clinical, relevance. We also replicated several previously reported marijuana loci, i.e., AHRR, ALPG, F2RL3, and MYO1G, in this mixed sex and self-reported race study sample, although additional studies in more diverse populations are needed to further evaluate previously associated epigenetic markers. Additionally, we observed differential DNA methylation levels by self-reported race and tobacco smoking status. While regression coefficients were highly correlated during stratified analyses, these findings provide insight into the interactive roles of self-reported race and tobacco smoking on marijuana associated methylation markers. For example, recent and cumulative marijuana use tended to exhibit greater hypomethylation of cg05575921 among Black participants and nonsmokers compared to White participants and former and current smokers, respectively. For the latter finding, the hypomethylation of cg05575921 during pooled and stratified analyses by tobacco smoking status suggests marijuana’s association with methylation may be consistent and independent of tobacco smoking. Our results highlight the interactive influences of biological and environmental factors on methylation signatures and provide insight into the differing impact of marijuana on the epigenome by population strata. These findings may serve as potential biomarkers to identify recent and long term marijuana use and molecular targets for further investigation. The epigenome is dynamic and responsive to environmental and lifestyle factors throughout the lifespan. Due to the ever changing nature of the epigenome, evaluating differences in methylation patterns across time not only enables the temporal assessment of a phenotype and epigenetic changes in the context of the natural history of a disease, but also permits examination of intra- and inter-individual variability and trajectories in methylation patterns over time.