We were not able to examine the quantity of marketing items . Lastly, our findings may not be applied to RMDs around adolescents’ homes, adolescents in private schools, or jurisdictions outside of California. With the dynamics in marijuana retail environments and government surveillance and law enforcement, the findings in the early stage of recreational marijuana commercialization may also lack generalizability to the most recent regulatory and retail contexts.Epidemiologic data indicate US young adult smokers use marijuana in greater amounts that their non-smoking peers. In 2009, 34.6% of smokers aged 18 to 25 reported past-month cannabis use compared with 8.9% of young adult nonsmokers. Depending on definitions of use, tobacco use increases the risk of cannabis use from 2 to 52 times in adolescents, and 3 to 6.4 times in adults. Demographic differences have been observed in patterns of tobacco and marijuana involvement among young adults. Older youths, males , students in vocational schools, and those living in the Northeast and in small metropolitan areas are more likely to use tobacco or cannabis. There is a need to examine more detailed patterns of tobacco and marijuana use to understand the complex relationship between these two substances. The internet is increasingly used in survey research of substance use with benefits over face-to-face interviews including broader reach; greater inclusion of low-incidence or “hidden” populations; rapid, best way to cure cannabis convenient input by respondents; and reduced bias in response to sensitive, potentially stigmatizing topics including illicit substance use.
Young adults remain the age group most likely to use the internet , and they are less likely, compared to other age groups, to present to traditional research settings for studies of health behavior . Our prior research has demonstrated the reliability and validity of anonymous online surveys of young adult tobacco and cannabis use. Analyzing data from an anonymous online survey of young adult smokers with national coverage, the present study examined the prevalence of past-month marijuana use, frequency among past-month marijuana users, and the frequency of co-using tobacco and marijuana. The large sample permitted analyses by gender, age, ethnicity, geographic region, urban/rural designation, student status, household income, daily smoking status, and by whether or not respondents resided in a state where marijuana is legal for medicinal use.Data for the present study were taken from a national cross-sectional survey using a convenience sample of young adult smokers. Briefly, young adults between the ages of 18 and 25, who reported smoking at least one cigarette in the past 30 days, were recruited online between 4/1/09 and 12/31/10. Three recruitment methods were used: 1) a paid advertisement campaign on Facebook; 2) a free campaign on Craigslist; and 3) a paid email advertising campaign through a survey sampling company. Participant entries could be tracked to which advertisement type they viewed . Only entries from advertisements targeting tobacco use were used in the present study so as not to inflate the prevalence of marijuana use in this population. Advertisements invited young adults to participate in a 20-minute online survey on tobacco use with a chance to win a prize in a drawing worth either US $25 or $400.
Advertisements contained a hyperlink directing potential participants to the study’s institutional review board -approved consent form, which mentioned assessment of marijuana use; to a screener for eligibility criteria; and to a secure online survey with data encryption for added security. Computer IP addresses were tracked, and only one entry was allowed from a single computer to prevent duplicate entries from the same person; however, multiple entries were allowed from the same internet connection .During the recruitment period, the online survey received more than 6423 hits, and 6176 people gave online consent to determine eligibility; of these, 3512 were eligible and deemed to be valid cases. Of eligible and valid cases, 2998 completed information about demographic and tobacco use only, and 1808 completed the entire 20–30 minute survey. Those who completed the survey differed from those who didn’t on some demographic variables, but the differences were small . The majority of the sample was male , Caucasian , living in an urban area , not currently a student , and smoked marijuana daily . Among current smokers, the overall prevalence of marijuana use was 53%. There was a significantly higher prevalence of marijuana use among males compared with females; among those aged 18 to 20 compared with those aged 21 to 25; among those with higher household income; among those living in urban versus rural areas; and among non-daily versus daily smokers.
There were no differences in prevalence of recent cannabis use by ethnicity, census region, residence in a medical marijuana state, or student status. Among past-month marijuana users, the median number of days using marijuana was 18.0 in the past 30 days . Non-students used marijuana on significantly more days than students, and daily smokers used on significantly more days than non-daily smokers. There were no differences in the number of days using marijuana in the past month by gender, age, ethnicity, household income, region, urban versus rural residence, or residence in a medical marijuana state. The proportion of days using both substances out of all past-month using days was a median of 45.5% . There was a higher proportion of tobacco and marijuana co-use among Caucasian respondents compared with those of other ethnic groups, among those residing in the Northeast compared to other census regions, among those residing in rural versus urban areas, among non-students, and among daily versus non-daily smokers . There were no differences in percentage of days with co-use by gender, age, household income, or residence in a medical marijuana state. The findings from this online anonymous survey of young adult smokers with national coverage indicate a greater prevalence of marijuana use than has been reported in epidemiological studies using household interviews. For example, in 2009, the US Substance Abuse and Mental Health Services Administration National Survey on Drug Use and Health reported that 34.6% of past-month smokers age 18 to 25 used marijuana, compared with 53.1% reported in the present study. The present sample was recruited online, primarily through social media, and the survey was completely anonymously, potentially allowing for reduced bias in reporting of illegal substance use . High prevalence of use was observed across demographic groups and regions, suggesting the issue of marijuana and tobacco co-use is of national relevance. The highest prevalence of marijuana use was observed among males, younger people, those with a higher household income and living in urban areas, and non-daily tobacco smokers. Consistent with previous epidemiological studies, young adult males tended to use marijuana at higher levels than young adult females, and young adults tended to reduce substance use as they reached developmental milestones of emerging adulthood, including leaving home, obtaining stable employment, cannabis drying kit and starting a family. Greater use among those in urban areas and from wealthier households reflects factors related to availability and is also consistent with national trends from household survey data. Notably, although daily tobacco smokers were slightly less likely to use marijuana than non-daily smokers, when they did use, they used it more frequently. There was a two-fold greater frequency of use among daily smokers compared with non-daily smokers and elevated frequency of use among non-students. Non-students and daily smokers also had greater co-use. Given the potential for detrimental effects of co-use among daily smokers, these findings support the broadening of interventions for daily tobacco smokers to consider use of both substances. Future research should examine the potential for substitution or compensatory effects during attempts to quit either substance. Study limitations include convenience sampling and self-reported data; however, face-to-face surveys often similarly rely on self-reported drug use, and we have previously demonstrated strong reliability and validity of tobacco and marijuana online surveys with young adults. The survey completion rate in this study was comparable to online survey studies with young adults but lower than that typically seen in nationally representative surveys. For example, weighted response rates for the 2010 SAMHSA-sponsored National Survey on Drug Use and Health were 88.8% for household screening and 74.7% for household interviewing.
Our respondents could leave the survey at any time; methods considered to encourage completion would have compromised participant anonymity. Sampling procedures and online data collection could have led to higher prevalence of marijuana use and co-use than is typical of representative surveys that have procedures to increase response rates .Marijuana is the most widely used illicit intoxicant and a significant public health concern for adolescents. Almost half of 12th graders have tried marijuana, with 5% reporting daily use . Early marijuana involvement can be particularly problematic, as use before age 15 is associated with a seven fold increased risk of developing a substance use disorder in the future . Concomitant alcohol and marijuana use is common, as 58% of adolescent drinkers also use marijuana . Animal studies have demonstrated cellular changes associated with chronic cannabis exposure, especially in prefrontal, hippocampal, and cerebellar regions among mice , rats , and primates . Two studies reported both gray and white matter abnormalities in several brain regions among young adult marijuana users , although findings reported by Aasly and colleagues may have been attributable to alcohol use. In contrast, Block and colleagues, in a study excluding individuals with histories of heavy drinking, did not find structural brain abnormalities among cannabis users . Recent functional neuroimaging studies on adults have found prefrontal, hippocampal, and cerebellar functioning abnormalities among marijuana users . However, the long term effects of chronic cannabis use, as opposed to acute effects, are less characterized. In a meta-analysis examining 11 studies, Grant and colleagues found that chronic cannabis use was associated with persistent but subtle deficits in learning and memory, but not in other cognitive domains. Other studies have demonstrated persisting deficits in processing speed, attention, working memory, visuospatial skills, and executive functioning . However, some studies found no persisting cognitive deficits among adults with histories of heavy marijuana use , and one study found that observed neurocognitive deficits normalized within a month of abstinence . Because neuromaturation continues through adolescence , results based on adults cannot necessarily generalize to adolescent marijuana users. White matter develops into the late 20s . Concurrently, gray matter volume peaks around ages 12–14 then decreases, due largely to synaptic pruning in the striatum and frontal lobe anterior to the motor strip , frontal poles, and lastly in the dorsolateral prefrontal cortex , which also is late to myelinate . Furthermore, adolescence may be a period of vulnerability to the neurocognitive effects of drug and alcohol use . For example, CB1 cannabinoid receptor levels in animals peak in early adolescence , cannabis-exposed adolescent rats are more vulnerable to learning impairments compared with exposed adult rats , and early adolescent onset of use is associated with increased morphometric and cognitive abnormalities in adult marijuana users . Despite the high prevalence of marijuana use, few studies have examined neurocognitive functioning in heavy marijuana using adolescents . Recently, we examined hippocampal volume and asymmetry and verbal memory among 63 adolescents . Similar to Tzilos and colleagues , we found that marijuana and alcohol using adolescents did not significantly differ from controls in hippocampal volume. However, we did find that the correlations between hippocampal asymmetry and verbal learning were abnormal among the marijuana users compared with the non-drug using controls. More specifically, increased right greater than left hippocampal asymmetry was associated with improved verbal learning among the controls, while no significant correlations between structure and function were found among marijuana users. Consistent with the adult literature , functional neuroimaging studies have found abnormal frontal, temporal, and parietal activation patterns among adolescent marijuana users compared with controls in response to verbal working memory and spatial working memory tasks. With few exceptions , neuropsychological studies focusing on adolescent substance abusers have found persisting cognitive deficits associated with heavy marijuana use. In an inpatient treatment study, marijuana-dependent adolescents demonstrated short-term memory decrements after 6 weeks of abstinence compared with polydrug users and controls . Marijuana using adolescents have also demonstrated increased perseverative responding on a problem solving task compared with control adolescents . A longitudinal investigation by Tapert and colleagues followed 47 polysubstance users and 26 normal controls over 8 years, from ages 16 to 24.