began,7 and families of children with microcephaly, organized in WhatsApp or Facebook groups, are active in shaping demands for their needs, including better support to access existing services.

A CHALLENGE What is the role for international public health, and can we achieve all of this in the current political climate, in which austerity

is so often chosen over provision of services? This is our gauntlet. Laura C. Rodrigues, PhD ACKNOWLEDGMENTS The author is partially funded by the European Union’s Horizon 2020 research and innovation program under ZikaPLAN grant agreement No. 734584.

REFERENCES 1. Chan M. Zika: we must be ready for the long haul. Available at: http://www.who. int/mediacentre/commentaries/2017/ zika-long-haul/en. Accessed March 7, 2017.

2. Teixeira MG, Costa Mda C, de Oliveira WK, Nunes ML, Rodrigues LC. The epidemic of Zika virus–related microcephaly in Brazil: detection, control, etiology, and future scenarios. Am J Public Health. 2016;106(4): 601–605. 3. Paixão ES, Barreto F, Teixeira Mda G, Costa Mda C, Rodrigues LC. History, epidemiology, and clinical manifestations of Zika: a systematic review. Am J Public Health. 2016; 106(4):606–612. 4. Miranda-Filho Dde B, Martelli CM, Ximenes RA, et al. Rodrigues LC. Initial description of the presumed congenital Zika syndrome. Am J Public Health. 2016;106(4): 598–600.

Changing Demographics of Marijuana Initiation: Bad News or Good? See also Miech et al., p. 996.

In demonstrating that the rate of marijuana initiation during college has undergone a recent and noteworthy increase, Miech et al. have documented an important social trend related to the prevalence and age at initiation of marijuana use.1 The authors present results from follow-ups of the annual 12th grade samples from Monitoring the Future in which they found that the prevalence of marijuana use among college students who did not initiate use before 12th grade sharply increased during the 2013 to 2015 period. This phenomenon was not observed among non–college students, leading the authors to conclude that college is becoming an increasingly important risk factor for marijuana initiation. Understanding trends in marijuana initiation is critical because initiation rates are an important component of overall prevalence. However, because the authors focus only on relatively late initiation, contrasting college students with similarly aged non–college students, their

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findings do not necessarily portend an overall increase in initiation among the full population. By way of analogy, an increase in the rate of sexual initiation among college students might stem from a wave of late initiators thereby contributing to an increase in the proportion of sexually active young adults. But it might instead indicate that college-bound youths were increasingly forgoing sexual activity until college. There would be no way to discriminate between these two strikingly different interpretations without examining trends among younger adolescents rather than focusing on the minority who initiate sexual activity later in adolescence. Definitive interpretation of the trend in college-age marijuana initiation likewise requires examination of a broader range of initiation ages because those who initiate use during or after 12th grade constitute a minority of users. Figure 1 provides such an analysis with data from 20- to 22-year-old participants from the

National Survey on Drug Use and Health, years 2002 to 2014, categorized according to whether they were currently enrolled in college full time or not. (Further sample details are available in Grucza et al.2) Figure 1 plots the lifetime prevalence of use among college students by year, partitioned by reported age at initiation into “early initiators,” who used before age 17, and “late initiators” who first used at age 17 years or older. Although prevalence was relatively stable for the 2002 to 2014 period, the composition of everusers shifted: most lifetime users were early initiators from 2002 to 2004, but late initiation overtook early initiation in 2006. There was a sharp increase in late initiation in the last few years of the series, but this was offset by a decrease in early initiation. More modest shifts from early to late initiation

5. Rodrigues LC. Zika: the tragedy and the opportunities. Am J Public Health. 2016;106(4):582. 6. Osorio-de-Castro CGS, Miranda ES, Carlos Machado de Freitas CM, de Camargo KR Jr, Cranmer HH. The Zika virus outbreak in Brazil: knowledge gaps and challenges for risk reduction. Am J Public Health. 2017;107(6):960–965. 7. Aiken AR, Scott JG, Gomperts R, Trussell J, Worrell M, Aiken CE. Requests for abortion in Latin America related to concern about Zika virus exposure. N Engl J Med. 2016;375(4): 396–398.

were observed for similarly aged noncollege individuals (omitted from Figure 1 for clarity). Results presented here are highly consistent with those of Miech et al., but provide an important context: if college has become a risk factor for late initiation, then college boundedness has become a protective factor against early initiation. In neither case are the risk or protective factors necessarily causal. Rather, the trends among college students and their similarly aged peers may stem from an overall shift toward later initiation; the shift may be stronger among college-bound youths for reasons not directly related to educational trajectory such as socioeconomic status. A trend toward later initiation is consistent with recent findings documenting decreased prevalence of adolescent marijuana use disorder, which is strongly associated with early initiation, over the 2002 to 2013 period.2 These changes may be part of a broader social trend

ABOUT THE AUTHOR Richard A. Grucza is with the Department of Psychiatry, Washington University School of Medicine, St Louis, MO. Correspondence should be sent to Richard A. Grucza, PhD, Department of Psychiatry, Washington University School of Medicine, 660 S Euclid Ave, Box 8134, St Louis, MO 63110 (e-mail: [email protected]). Reprints can be ordered at http://www.ajph.org by clicking the “Reprints” link. This editorial was accepted March 16, 2017. doi: 10.2105/AJPH.2017.303804






Prevalence, %















Year Note. Points proximal to black line (top) represent total prevalence. Points proximal to gray line represent prevalence of “early initiation,” defined as use before the age of 17 years. Points proximal to short-dashed line represent prevalence of “late initiation,” defined as use beginning at age 17 years or older. Polynomial lines do not represent formal trend analyses and are included only to enable the reader to distinguish among series. Standard errors of estimates range from about 1% to 1.3%. The sample size was n = 32 763.

FIGURE 1—Lifetime Prevalence of Marijuana Use Among National Survey on Drug Use and Health Participants Aged 20–22 Years Enrolled as Full-Time College Students: United States, 2002–2014

toward lower rates of multiple health-risk behaviors during adolescence, such as delinquency, early sexual debut, binge drinking, and other drug use.2,3 The interpretation given here bears some similarity to that provided by Miech et al. who acknowledge “a shift in the age range of marijuana initiation toward young adults.”1(p1001) The authors suggest that the increase in college initiation may herald significant population-level increases in marijuana use, but viewing their findings as a result of an upward shift in age of initiation carries no such implication and could be viewed as a positive development. If the majority of




adults in the United States try marijuana at some point in their lives—as has been the case for some time now—then part of the public health approach should be to delay initiation for as long as possible. This would also have the effect of limiting the total number of initiates as many people would mature out of the experimentation phase without initiating marijuana use. The analyses of Miech et al. are motivated by the “signaling hypothesis,” attributed to a somewhat controversial 1995 editorial by DuPont and Voth, who asserted that any reductions in criminal penalties for drug use would increase risk for young

people, presumably by sending the “wrong signal.”4 DuPont and Voth did not intend to generate a hypothesis for future scientific evaluation, so it is unclear what the signaling hypothesis predicts in terms of the timing of effects, the affected outcomes, the impacted age groups, or the geographic boundaries of the signals. Miech et al. justify their focus on recent college cohorts by arguing that legalization of recreational marijuana in a number of states sent a signal that marijuana is “safe and state sanctioned,” and that college students are particularly receptive to such messages. The authors’ previous work claiming support for the signaling hypothesis focused on high-school students.5 Thus, if the increase in college student initiation is taken as support for the signaling hypothesis, then the decline in early initiation noted here must be taken as counterevidence. Furthermore, medical legalization laws would seem to send the ultimate signal of safety and state approval by implying that marijuana has some health benefits. The fact that their passage does not seem to have resulted in large increases in youth marijuana use presents a significant challenge to the signaling hypothesis (e.g., see Wall et al.6 ). If the signaling hypothesis is to be used as a theoretical framework, greater clarity is needed about its specific predictions. In conclusion, the observation of increased rates of marijuana initiation among college students warrants vigilance, but these increases are not necessarily attributable to campus environmental factors or to policy liberalization and they may not lead to higher rates of marijuana initiation in

the full population. Furthermore, the public health implications are not clear until we know whether any such increases in experimentation are accompanied by higher rates of heavy use and dependence and what they imply for misuse of alcohol and other drugs. Given that later initiation is associated with decreased risk for drug-related problems, there may even be a case for cautious optimism.7 Richard A. Grucza, PhD

REFERENCES 1. Miech R, Patrick ME, O’Malley PM, Johnston LD. Does going to college put students at higher risk for marijuana initiation? A growing trend. Am J Public Health. 2017;107(6):996–1002. 2. Grucza RA, Agrawal A, Krauss MJ, et al. Declining prevalence of marijuana use disorders among adolescents in the United States, 2002 to 2013. J Am Acad Child Adolesc Psychiatry. 2016;55(6):487–494.e6. 3. Johnston LD, O’Malley PM, Bachman JG, Schulenberg JE. Monitoring the Future national results on drug use: 2013 overview, key findings on adolescent drug use. Ann Arbor, MI: Institute for Social Research, University of Michigan; 2014. 4. DuPont RL, Voth EA. Drug legalization, harm reduction, and drug policy. Ann Intern Med. 1995;123(6):461–465. 5. Miech RA, Johnston L, O’Malley PM, Bachman JG, Schulenberg J, Patrick ME. Trends in use of marijuana and attitudes toward marijuana among youth before and after decriminalization: the case of California 2007–2013. Int J Drug Policy. 2015;26(4):336–344. 6. Wall MM, Mauro C, Hasin DS, et al. Prevalence of marijuana use does not differentially increase among youth after states pass medical marijuana laws: commentary on Stolzenberg, et al. (2015) and reanalysis of US National Survey on Drug Use in Households data 2002–2011. Int J Drug Policy. 2016;29:9–13. 7. Robins LN, Przybeck TR. Age of onset of drug use as a factor in drug and other disorders. NIDA Res Monogr. 1985;56:178–192.


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Changing Demographics of Marijuana Initiation: Bad News or Good?

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