Congress Should Not Legalize Marijuana, Marco Rubio Says, Because Black-Market Weed Is 'Laced With Fentanyl'

The Florida senator has a long history of defending prohibition, but it has not improved his arguments.

When Sen. Marco Rubio (R–Fla.) was seeking the 2016 Republican presidential nomination, a local paper noted that he had "a long history speaking out against marijuana legalization." Given that history and the fact that Rubio's position is rejected by two-thirds of Americans, you might think he would be prepared to defend marijuana prohibition with cogent arguments.

If so, you would be wrong. In a recent interview with a Pensacola TV station, Rubio worried that legalization would encourage teenagers to use cannabis, which would be a "gateway" to other drugs, and warned that black-market marijuana is "laced with fentanyl." All three arguments are logically and empirically dubious. If this is the best that Rubio can do, he'd be better off changing the subject.

"When you decriminalize something, the message that you're basically sending people is it must not be that bad," Rubio said. "Now, suddenly, you're an 18- or 17-year-old, [and you] say, 'Well, I know marijuana, you tell me not to smoke it, but you know what? It can't be that bad, because the federal government made it legal.' And so all of a sudden now, you're going to have a problem in this country, because that becomes a gateway. We know that marijuana use is often the first thing that people use before they move on to something else. We've also seen, by the way, marijuana being purchased off the streets that's laced with fentanyl and other drugs, and it's killing people."

We obviously don't know yet what impact repealing the federal ban on marijuana would have on the impressionable teenagers that Rubio imagines. But there is little evidence that legalizing marijuana for medical or recreational use at the state level, as 37 states already have done, has boosted underage consumption.

A 2013 study published in the American Journal of Public Health found that medical marijuana laws "have not measurably affected adolescent marijuana use in the first few years after their enactment." A 2014 study published in the Journal of Adolescent Health likewise "did not find increases in adolescent marijuana use related to legalization of medical marijuana." Similar results have been reported in The Lancet Psychiatry (2015), Drug and Alcohol Dependence (2017), Addiction (2018), and The American Journal of Drug and Alcohol Abuse (2019).

The research on recreational legalization is a bit more mixed, but the weight of the evidence does not support Rubio's concern. A 2017 JAMA Pediatrics study found that cannabis consumption by eighth- and 10th-graders rose slightly in Washington state after recreational use was legalized but stayed the same in Colorado. A 2018 study reported in Substance Abuse: Research and Treatment found "no significant differences" in adolescent substance use before and after recreational legalization in Washington, although "there were significant post-policy increases in problems and use disorder symptoms." A 2019 Prevention Science study "did not find a significant effect associated with the introduction of legal sales of recreational marijuana to adults in Colorado on adolescent (illegal) use."

A 2018 APA PsycNet study found evidence that legalization of recreational marijuana in Oregon "did not increase marijuana use for youth who did not use marijuana but did increase use in youth who were already using." A 2019 study reported in JAMA Pediatrics, based on data from the Youth Risk Behavior Survey (YRBS), found "there was no evidence that the legalization of medical marijuana encourages marijuana use among youth" and said "marijuana use among youth may actually decline after legalization for recreational purposes."

A 2019 systematic review and meta-analysis in BMJ Open found the studies suggested "a small increase in cannabis use among adolescents and young adults following legalisation of cannabis for recreational purposes." But it noted that "studies characterised by a very low/low risk of bias showed no evidence of changes in cannabis use following policy modifications."

According to a 2021 analysis published in the Journal of Adolescent Health, YRBS data "suggest minimal short-term effects of [recreational legalization] on adolescent substance use, with small declines in marijuana use and increase in the likelihood of any e-cigarette use." Yet another study based on YRBS data, reported in JAMA Network Open last year, found "there were no significant associations between enactment of [recreational or medical legalization] and marijuana use among high school students."

What about Rubio's fear that marijuana is a "gateway" to more dangerous drugs? Rubio probably knows from personal experience that the vast majority of people who smoke pot don't become heroin addicts. Taking a page from George W. Bush, Rubio has refused to say whether he smoked pot in his youth, based on a rationale that implicitly concedes he did: "If I tell you that I did, then kids will look up to me and say, 'Well, I can smoke marijuana, because look how he made it.'"

That's a dangerous message, Rubio thinks, because those kids, unlike him, might find that pot is the first step on the road to ruin. But while the "gateway drug" trope has been popular among pot prohibitionists since the 1950s, the issue is much more complicated than Rubio suggests.

It is true that marijuana "is often the first thing that people use before they move on to something else." It is also true that people who try marijuana are more likely to try other drugs than people who never try marijuana. But that does not mean marijuana use causes people to "move on to something else." Many studies have tried to distinguish between correlation and causation by controlling or adjusting for confounding variables, with mixed and contentious results.

The psychologist Andrew Morral and his colleagues at the RAND Drug Policy Research Center have shown that an underlying propensity to use drugs, combined with the relative availability of different intoxicants, could entirely account for the three phenomena emphasized by advocates of the gateway theory: 1) that people tend to use marijuana before other illegal drugs, 2) that people who use marijuana are more likely to use other illegal drugs, and 3) that the likelihood of progression increases with the frequency of marijuana use. Their mathematical model did not disprove the gateway theory, but it did prove that the gateway theory is not necessary to explain these observations. Morral et al. concluded that "available evidence does not favor the marijuana gateway effect over the alternative hypothesis that marijuana and hard drug initiation are correlated because both are influenced by individuals' heterogenous liabilities to try drugs."

I suspect that Rubio is about as familiar with research on the gateway theory as he is with research on how legalization affects adolescent marijuana use. But his third argument against legalization, which hinges on the hazards of marijuana "laced with fentanyl and other drugs," can be debunked without delving into the scientific literature, because it plainly makes no sense.

It is worth noting that fentanyl-laced marijuana may be nothing more than "an urban legend," as an intelligence officer with the New England High Intensity Drug Trafficking Area put it. But even if it were a real and significant threat, it would be entirely a product of the black market created by prohibition. Legalization—the very policy that Rubio ostensibly is arguing against—is the most effective way to assure cannabis consumers that their pot is not mixed with something they neither expect nor want. Rubio's obliviousness to that point speaks volumes about the logically and scientifically bankrupt foundation of the policy he thinks he is defending.