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标题：Birth Cohorts Analysis of Adolescent Cigarette Smoking and Subsequent Marijuana and Cocaine Use
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作者：Katherine M. Keyes ; Ava Hamilton ; Denise B. Kandel 等
期刊名称：American journal of public health
印刷版ISSN：0090-0036
出版年度：2016
卷号：106
期号：6
页码：1143-1149
DOI：10.2105/AJPH.2016.303128
语种：English
出版社：American Public Health Association
摘要：Objectives. To examine whether the drug behavior of adults from different birth cohorts is shaped by adolescent drug experiences and whether adult prevalence of marijuana and cocaine use depends on adolescent cigarette or alcohol use prevalence. Methods. We analyzed 18 birth cohorts comprising 8th, 10th, and 12th graders, sampled from 1991 to 2008, from Monitoring the Future, an annual nationally representative cross-sectional survey of high school students in the United States (n = 864 443). Results. Within cohorts, lifetime rates of 8th and 10th grade cigarette use were significantly associated with subsequent lifetime rates of marijuana and cocaine use, controlling for trends in use and social norms toward drug use. Each percent increase (or decrease) in 8th and 10th grade smoking was associated with an 8% increase (or decrease) in prevalence of later marijuana use and 14% to 23% increase (or decrease) in prevalence of later cocaine use. Relationships were consistent by gender and race/ethnicity. Conclusions. Prevalences of smoking in 8th and 10th grade and of marijuana and cocaine use in 12th grade are associated. Public health campaigns should focus on early stages of adolescence, when drug use habits are forming. Drug use often starts in adolescence with a drug that is legal for adults and proceeds to illegal drugs. Typically, the use of alcohol or tobacco precedes the use of marijuana, which in turn precedes the use of cocaine and other illicit drugs. 1–7 This sequence has been observed even in recent periods, when the prevalence of marijuana use among young people has greatly increased and even surpassed that of cigarette use. Among high school seniors in 2014, 66.0% reported ever drinking alcohol, 34.4% smoking cigarettes, 44.4% using marijuana, and 4.6% using cocaine. 8 Of the marijuana users, 47.2% smoked or drank alcohol before using marijuana, 37.3% started in the same grade, 11.3% started using marijuana before smoking or drinking, and 4.2% never smoked nor drank. Parallel percentages for cocaine users were 84.4%, 10.4%, 2.8%, and 2.4%, respectively. This progression has led to the notion that drugs, such as alcohol and tobacco, can be considered to be “gateways” to the use of other drugs. 1–3,6 However, although most cocaine users have smoked cigarettes, very few smokers progress to cocaine; only 11.6% did so by 12th grade compared with 0.8% of nonsmokers. An alternate interpretation is that the use of multiple drugs reflects a common liability for drug use, which itself, rather than using a particular drug, increases the risk of using another drug. 9 Generalized risks include common genetic predispositions, psychosocial factors conducive to using any drug, and environmental factors, including drug availability, opportunities for use, and societal norms favorable to drug use. 4,10–14 Both generalized risk across drugs and drug-specific risk, attributable particularly to tobacco use, have been identified. 5 Although common factors may explain the use of drugs in general, specific factors may explain why young people use specific drugs and in a particular sequence. Evidence supporting a causal mechanism for the sequence between 2 drugs derives from translational research. Nicotine pretreatment in mice enhances the subsequence response to later cocaine exposure but not vice versa. 15 Nicotine exerts a priming effect on cocaine through increased global histone acetylation in the striatum of the nucleus accumbens, creating an environment primed for induction of gene expression. Similarly, mice exposed to nicotine in early adolescence showed increased conditioned place preference for cocaine in adulthood through induced AFosb expression. 16 The results provide a biological basis and a molecular mechanism for the sequence of drug use observed in people: one drug affects the circuitry of the brain in a manner that potentiates the effects of a subsequent drug. 15,17 At the population level, if the order of drug use onset is relevant, the drug behavior of adults at different historical periods will vary as a function of the prevalence of specific drugs used in adolescence. Degenhardt et al. 6 used a similar argument on the basis of examining the impact of variations in adolescent drug behavior across 17 countries during the same historical period. Prevalence of adolescent smoking and alcohol use predicted use of other drugs by age 29 years. We hypothesized that birth cohorts in which a higher percentage of adolescents smoked cigarettes early in adolescence would also have a higher prevalence of marijuana and cocaine use in later adolescence and early adulthood; the reverse would hold for birth cohorts with a lower prevalence of smoking in adolescence. To test the hypothesis, longitudinal data from different birth cohorts followed from adolescence to adulthood would be optimal. However, repeated cross-sectional surveys from representative national samples are a suitable alternative, because age groups in successive surveys are random subsamples of their respective birth cohorts. It is also important to control for other common causal explanations of the associations, such as social norms regarding drug use. Observed patterns may reflect changing norms about all forms of drug use in each birth cohort. Increases in negative norms in a birth cohort would produce lower rates of smoking in adolescence and lower rates of marijuana and cocaine use in adulthood. We examined sequential patterns of drug use over a short interval from early to late adolescence by taking advantage of historical variations in rates of cigarette use in early adolescence and repeated nationally representative surveys of drug use among high school students spanning 22 years. We examined the lifetime marijuana and cocaine use of 12th graders as a function of levels of smoking experienced 2 or 4 years earlier by 8th or 10th graders in 18 birth cohorts sampled from 1991 to 2008. These cohorts spanned a period of lower smoking prevalence among 8th graders (44.0%) in 1991, a period of peak prevalence (49.2%) in 1996, and a period of much lower prevalence (20.5%) in 2008. We implemented analysis by gender and race/ethnicity. African Americans appear to be less likely than are Whites to follow the sequence from tobacco to marijuana, 18 although the sequence has been observed in community samples. 19