Gateway Hypothesis

A substantial body of research supports the gateway hypothesis of drug use. In 2014, a watershed study identified a biological process through which administering one drug influenced the reaction to a second drug. In the study, mice given nicotine in their water over a period of time showed addiction-related genetic changes and increased vulnerability to cocaine dependence.^{Reference Kandel and Kandel7}

In this issue of the Journal of Law, Medicine & Ethics, Arthur Williams argues that cannabis is a gateway drug for opioid use disorder.^{Reference Williams8} He presents several key findings from the scientific literature to support his claim. He cites the earlier work of the Kandels (2014), noted above, and more recent lines of research that suggest the role marijuana might have as a gateway to opioids. Research has found several reasons to believe that the endocannabinoid and endogenous opioid systems in the brain interact.^{Reference Orr, Spechler and Cao9} Williams discusses how marijuana use can worsen mental health outcomes for some individuals, producing anxiety, depression, cognitive deficits, and psychosis. He also raises concerns about adolescent marijuana use, concluding that marijuana use during adolescence may increase the risk for initiation of opioid use and subsequent development of opioid use disorder for some vulnerable individuals.

The gateway hypothesis is not without its critics, however. Scholars have examined the history and application of the gateway hypothesis and argued that it should be retired from use because it involves an oversimplification of the dynamics.^{Reference Kleining10} Williams similarly discusses the multifactorial causes of substance use disorder: for example, trauma, genetic and familial risk, environmental risk factors (e.g., social networks, exposures), and untreated psychiatric comorbidity.¹¹ The framing of the debate around the gateway hypothesis of drug use is a distraction from other important issues, such as research. For example, Williams argues that the important question is not whether the gateway theory exists, rather, it is how we can develop research to best identify which adolescents are at risk and focus on trauma, mental health, and protective environments. Finally, some critics of the gateway hypothesis believe that instead of prohibiting marijuana use, we should accept its use based on ethical grounds of personal autonomy and political grounds of individual liberty.^{Reference Sullum12} These two factors underlie the growing movement toward liberalization of marijuana policy, as more jurisdictions across the U.S. continue to legalize marijuana. At this time, only nine states treat marijuana as fully illegal, while 41 states have enacted laws to: fully legalize (10, plus District of Columbia), decriminalize (3), legalize for medical use only (17), or decriminalize and legalize for medical use (11).¹³

Policy Recommendations

Public health research provides important lessons for policymakers who are considering legalizing marijuana.^{Reference Pacula, Kilmer, Wagenaar, Chaloupka and Caulkins14} Legalization of marijuana has often been accompanied by marketing campaigns that target adolescents and young adults, who are regularly exposed to marketing for recreational use on social media.^{Reference Trangenstein, Whitehill and Jenkins15} To counter advertisements of marijuana products, policy-makers in states that legalize marijuana should design marketing campaigns to educate the public about the potential adverse effects of marijuana use, particularly by adolescents and young adults. Adolescence and young adulthood are critical times for brain maturation because of ongoing neurodevelopment. The process of pruning and remodeling that occurs in the brains of young adults can be affected by marijuana use.¹⁶ Adults who begin using marijuana before the age of 18 are four to seven times more likely to develop marijuana use disorder than adults who develop marijuana use disorder but did not use it before the age of 18.^{Reference Winters and Lee17} Marijuana use is similarly linked to other substance use disorders such as nicotine addiction.¹⁸ Therefore, an important public health strategy would be to restrict the supply of marijuana to adolescents. Doing so may reduce potential harmful use.

Based on information from alcohol and tobacco marketing studies,¹⁹ states legalizing marijuana should set aside funds from tax revenue collected from the marijuana industry to design and fund prevention and cessation programs aimed at reducing marijuana use by adolescents and young adults. Marijuana advertisements or drug delivery devices that are specifically designed to target the young should be prohibited. Several jurisdictions that have legalized marijuana for adult recreational use have regulated the sales of marijuana-infused edibles, citing concerns that their design and advertising focus on young people.^{Reference O'Connor, Mendez and Bess20} California, for example, has banned edibles resembling fruit, animals, or humans, and the products cannot be referred to as “candy.” Cartoons, images, or other messaging that potentially appeal to children are also not permitted.^{Reference McDonough21} More research is needed to examine the effectiveness of these policies.

Tobacco and alcohol studies have shown that targeting the supply of substances is a more effective approach for reducing use in youth than by focusing on possession.^{Reference Babor, Caetano and Casswell22} Williams has suggested that policy-makers should limit the supply of marijuana to children and young adults by setting a minimum age of sale and use at 25.²³ We disagree with such a proposal because doing so may risk reestablishing the long-standing black market that legalization has done so much to defeat. Recent research suggests that over-regulation in California, at both the state and local level, is bolstering the illicit marijuana market.^{Reference Gunelius24} Therefore, regulation of advertising and availability of marijuana-infused edibles and drug delivery devices to youths may be a better approach to curbing the harmful effects of marijuana use than a strict prohibition of use through age 25. Increasing the minimum-purchasing age for buying marijuana to at least 21 would be more reasonable, as this policy would be consistent with tobacco and other vapor-related products.

The science arising from this field of study is still relatively new and current research methodology is insufficient to address the rapid changes occurring in the legal marijuana market. As the market grows, new sources of data will become available to researchers. For example, the marijuana industry is producing a tremendous amount of information through seed-to-sale tracking systems, market surveys, delivery services, loyalty card programs, and other sources.²⁵ Policymakers should work closely with representatives of the marijuana industry to find ways to share data collected from these new sources with researchers, who can then develop evidence-based insights about these emerging markets.^{Reference Kilmer and Pacula26} To assist researchers in this process, the federal government should remove its prohibition of marijuana sales and allow federal funding of scientific research in this field. Doing so might facilitate uniformity of data collection across jurisdictions by reducing the likelihood of a patchwork of competing and conflicting regulations, and will help bring transparency to the marijuana industry.²⁷ Lifting the federal prohibition will also help marijuana dispensaries, which currently have a difficult time negotiating leases with landlords and finding banks willing to open business accounts. One undesirable side effect of banks' refusal to accept funds from marijuana vendors is that it has led to a high rate of cash transactions for marijuana sales. Managers at marijuana dispensaries have expressed concern for the safety of their employees because an all-cash business may attract criminal attention.²⁸