Prohibition Didn’t Stop Marijuana Use. It Stopped Marijuana Research.

On June 29, the Drug Enforcement Administration (DEA) will convene a hearing to consider whether marijuana should finally be removed from Schedule I of the Controlled Substances Act, the federal government’s most restrictive drug classification, reserved for substances with a high potential for abuse and no accepted medical use. Heroin and LSD are in the same category. This hearing will determine whether restrictions will be eased on marijuana as a whole.  

It’s a strikingly late debate to be having. 

The proceedings, which must conclude by July 15, follow an April order from the Department of Justice that moved marijuana products approved by the Food and Drug Administration (FDA) and state-licensed medical marijuana into Schedule III, a less restrictive category that allows medical research to proceed. Tens of millions of Americans use marijuana today, and cannabis is sold legally in some form across most of the country. Yet we know far less about the drug than its ubiquity would suggest. For more than half a century, a classification that was never meant to be permanent has blocked the research needed to understand what marijuana actually does to the people who use it.

The origin of this problem is political, not scientific. When Congress passed the Controlled Substances Act in 1970, marijuana’s placement in Schedule I was explicitly provisional, a placeholder pending review by a presidential commission. The Shafer Commission, chaired by a Republican governor and composed largely of President Richard Nixon’s appointees, concluded in 1972 that marijuana did not meet the criteria for Schedule I and recommended decriminalizing personal possession. Nixon ignored the report and escalated the war on drugs. The provisional classification became permanent by default. Since 1965, an estimated 29 million Americans have been arrested on marijuana charges, roughly 90 percent of them for possession alone.

The most damaging consequence of Schedule I, however, has not been to cannabis users, who have gained access through state legalization, but to the research enterprise. Schedule I substances face the most restrictive regulatory barriers under federal law, including heightened DEA registration requirements, limited sourcing options, and protocol approvals that materially delay or deter research. Even DEA-registered researchers have been barred from using certain National Institutes of Health grants to purchase cannabis. The products available from government-approved suppliers have not represented the full range of what people actually consume at dispensaries. The classification, in effect, impedes research into drug safety, leaving the millions of cannabis users it claims to protect less informed than they would otherwise be.

And there is plenty we need to know. The strongest evidence of risk concerns psychosis, especially in young users. A multisite study published in The Lancet Psychiatry, drawing on data from 901 patients with first-episode psychosis across 11 European sites, found that daily cannabis use was associated with more than three times the odds of a psychotic disorder, rising to nearly five times for users of high-potency products containing over 10 percent THC, the primary psychoactive compound in marijuana. The authors estimated that one in five new psychosis cases across the study sites could be attributed to daily use. A 2022 systematic review of 20 studies covering nearly 120,000 cannabis users confirmed that higher-potency products are associated with elevated risk of both psychosis and cannabis use disorder.

The biological mechanism is plausible and concerning, particularly for young people. Adolescence is a critical window for brain development, marked by extensive synaptic pruning and the maturation of prefrontal circuits governing impulse control and decision making. The endocannabinoid system, the molecular network that THC activates, plays an essential role in these developmental processes. A 2025 review in the American Journal of Psychiatry concluded that translational research combining longitudinal neuroimaging with animal models provides compelling evidence that frequent cannabis use, particularly high-THC products, can disrupt adolescent brain development.

Meanwhile, the potency of commercially available cannabis has been rising steadily for decades, with average THC concentrations increasing by roughly 0.29 percent per year from 1970 to 2017. That trend aligns with what drug-policy analysts sometimes call the “iron law of prohibition“: When enforcement intensifies, producers and traffickers have incentives to favor more concentrated and potent products that are easier to transport, conceal, and distribute while generating greater returns relative to the legal risks involved. Today’s dispensary products bear little resemblance to the marijuana the Shafer Commission evaluated in 1972.

Prohibition may make youth cannabis access easier rather than harder. Illegal markets do not check identification, whereas licensed retailers risk losing their licenses for selling to minors. As long as recreational marijuana remains confined to illicit channels, teenagers will continue to obtain cannabis from suppliers who face no meaningful incentive to restrict underage access. It would be safer to have a legal market with age restrictions on marijuana sales, as with alcohol, nicotine, and other adult products.

Public opinion has moved faster than federal policy. According to a Pew Research Center survey conducted in January 2026, roughly nine in 10 American adults say marijuana should be legal in some form: 55 percent support legalization for both medical and recreational use, 33 percent support it for medical use only, and just 11 percent say it should not be legal at all. A 2025 Gallup poll found that 64 percent of Americans support making marijuana legal outright, more than double the level of support recorded in 2000, with no age group opposing legalization. Forty states, the District of Columbia, and several U.S. territories have legalized medical cannabis, and 24 states have legalized recreational use. More than 6 million patients are registered in state medical programs. Yet the federal classification persists, and so does the debate over whether and how to reform it.

The debate is not entirely one-sided. While Americans overwhelmingly support medical access, views on the broader consequences are more divided. According to a 2024 Pew report, 34 percent of adults said recreational legalization makes communities less safe, compared to 21 percent who said it makes them safer. About 29 percent believed it increases the use of harder drugs. These concerns are not irrational. But the current federal framework is poorly suited to resolving them, because the same classification system that is supposed to protect public health has, for decades, prevented the research that would tell us how worried we should actually be.

The medical marijuana system itself reflects a broader American tendency to force adult behavioral choices through medical gatekeeping structures. Millions of adults who simply want legal access to cannabis are effectively required in many jurisdictions to obtain physician certification for conditions that may be only loosely medicalized. When legal access to products, services, accommodations, or reimbursement depends upon obtaining a medical diagnosis, the boundary between illness and ordinary human behavior can become increasingly blurred. The physician’s role shrinks to that of regulatory intermediary, and with it collapses any meaningful distinction between medical treatment and adult lifestyle choice.

Schedule I classification has not stopped tens of millions of Americans from using marijuana, but it has made it extraordinarily difficult for scientists to study what happens when they do. The federal government has spent decades trying to suppress marijuana use while simultaneously obstructing the research needed to understand risks, benefits, dosing patterns, and long-term effects. Prohibition has not prevented widespread cannabis consumption. It has mainly ensured that policymakers, physicians, and consumers operate with less reliable evidence than they otherwise would.

Even so, the scientific case for medical cannabis has only strengthened. The FDA has approved one cannabis-derived drug (Epidiolex for severe pediatric epilepsy) and three cannabis-related synthetic compounds for chemotherapy-induced nausea and AIDS-associated wasting. A 2024 systematic evidence map reviewing 194 studies found that the majority of treatment effects across 71 distinct health outcomes were positive or potentially positive, with the strongest evidence for chronic pain, nausea, and spasticity. The Department of Health and Human Services recommended rescheduling in 2023, citing credible scientific support for medical use. In other words, the agency responsible for evaluating drug safety concluded that the government’s own classification was wrong.

Rescheduling marijuana to Schedule III does not legalize recreational use. It does not make cannabis available over the counter. What it does is substantially reduce the regulatory barriers to the research that informed policy requires. It will allow scientists to study the products people actually use, at the doses they actually consume, without years of DEA paperwork. President Donald Trump’s December 2025 executive order directing the attorney general to expedite rescheduling acknowledged as much, citing the need to remove barriers to medical research. If this summer’s hearing ends with marijuana as a whole in Schedule III, the research pipeline severed in 1972 can finally begin to be rebuilt.

Adults in a free society should be able to make informed choices about what they put in their bodies. But informed choice depends on information, and for half a century, the federal government has made it nearly impossible to generate the information needed to make those choices genuinely informed.