The legalization of marijuana is one of the largest drug policy shifts in American history. What began as a campaign to prohibit a substance through racial anxiety and economic interest has evolved, over nearly nine decades, into a situation where the majority of American states have programs allowing some or all cannabis use. Understanding how prohibition was established, how it eroded, what legalization has actually produced in terms of public health outcomes, and where federal policy stands today provides essential context for any serious engagement with cannabis issues.
Before Prohibition: Cannabis in American History
Cannabis was legal and widely used in the United States through most of the 19th and early 20th centuries. Hemp, a variety of cannabis with very low THC, was cultivated by early American farmers (including George Washington) for fiber. Medical cannabis preparations were listed in the U.S. Pharmacopeia from 1850 to 1942. Patent medicines containing cannabis were widely sold.
Recreational use of cannabis was prevalent in Mexican-American communities in the Southwest and South following the Mexican Revolution of 1910, as significant migration brought cannabis smoking culture northward. This association between cannabis and Mexican immigrants was deliberately exploited in early prohibition campaigns; the word ”marijuana” (rather than ”cannabis”) was promoted in anti-drug campaigns precisely because it sounded foreign and played on nativist anxieties. The term “Marihuana” in the 1937 legislation reflected this political framing.
By the mid-1930s, 35 states had adopted the Uniform State Narcotic Drug Act, effectively criminalizing cannabis at the state level. Federal action followed.
The Marihuana Tax Act of 1937
The federal government’s first major prohibition of cannabis came through the Marihuana Tax Act of 1937, championed by Harry Anslinger, the first commissioner of the Federal Bureau of Narcotics. The legislation was structured as a tax measure rather than an outright prohibition, similar to the Harrison Narcotics Tax Act of 1914 that had effectively prohibited opium and heroin, because Congress deemed tax-and-regulate legislation less susceptible to constitutional challenge.
The 1937 act imposed prohibitively high transfer taxes and registration requirements on cannabis dealers, manufacturers, and importers, effectively ending recreational use and severely curtailing medical and industrial hemp use. The American Medical Association actively opposed the bill, with legislative counsel Dr. William Woodward testifying that the evidence did not support claims that cannabis caused addiction or violence. Congress passed it anyway.
The political context for the 1937 act involved multiple overlapping interests: Anslinger’s institutional need for the FBN to expand its authority following the end of alcohol prohibition, the Hearst newspaper empire’s anti-cannabis advocacy (Hearst had invested heavily in timber for newsprint, competing with hemp paper), and the nativist and racist framing of cannabis as a “Mexican” and “Black” drug. The hearings included sensationalized testimony about cannabis-induced violence that had no credible evidentiary basis.
The Marihuana Tax Act remained in effect until 1969, when the Supreme Court struck it down in Leary v. United States as a violation of the Fifth Amendment’s protection against self-incrimination: a person seeking to pay the marijuana tax would have to incriminate themselves.
The Controlled Substances Act of 1970
Congress responded to Leary by enacting the Controlled Substances Act (CSA) of 1970 as part of the Nixon administration’s broader drug enforcement agenda. The CSA established a scheduling framework and placed marijuana in Schedule I, the category for substances with high abuse potential and no accepted medical use. This was explicitly described as a temporary placement pending the findings of the National Commission on Marihuana and Drug Abuse (the Shafer Commission), which Nixon had established to study the issue.
The Shafer Commission delivered its 1972 report, Marihuana: A Signal of Misunderstanding, recommending the removal of criminal penalties for possession and distribution of small amounts of marijuana. Nixon famously rejected the commission’s findings and initiated the War on Drugs, which sharply escalated marijuana enforcement rather than following the commission’s advice.
A widely reported 1994 admission by John Ehrlichman, Nixon’s domestic policy chief, described the original intent behind the War on Drugs explicitly: the Nixon campaign had two enemies, Black people and antiwar protesters, and by associating each with heroin and marijuana, “we could disrupt those communities” and “criminalize both heavily.” This historical record has shaped contemporary discussions of cannabis policy reform and racial justice.
The Long March Through the States: 1973–2012
The legalization movement began not with dramatic federal policy change but with incremental state-level decriminalization:
- 1973: Oregon became the first state to decriminalize cannabis, reducing the penalty for possessing up to one ounce to a $100 civil fine
- 1970s: Alaska, Maine, Colorado, California, and Ohio followed with decriminalization; several quickly reversed
- 1978: New Mexico approved a short-lived medical marijuana research program
- 1996: California Proposition 215 was the breakthrough, the first state law legalizing medical marijuana. California’s voters directly defied federal policy in what became the model for state-federal cannabis conflict
- 2000s: Medical programs spread to a growing number of states through ballot initiatives and legislative action
- 2012: Colorado Amendment 64 and Washington I-502, the watershed moment. Voters in both states approved full adult-use recreational legalization, becoming the first US states to create regulated recreational cannabis markets. These represented the first state-level legalizations in the world of recreational cannabis for adults
The Modern Legalization Era: 2012–2026
Colorado and Washington’s 2012 legalizations opened a cascade of state action:
- 2014: Alaska, Oregon, and Washington D.C. followed with adult-use legalization
- 2016: California, Nevada, Massachusetts, and Maine voted for recreational legalization; Florida and Arkansas expanded medical programs
- 2018: The 2018 Farm Bill legalized hemp (cannabis with ≤0.3% delta-9-THC), excluding it from the CSA and opening the CBD market
- 2020: Arizona, Montana, New Jersey, and South Dakota voted for adult-use legalization. New Jersey and others launched regulated markets by 2022
- 2022: The Medical Marijuana and Cannabidiol Research Expansion Act became law, the first standalone cannabis reform at federal level
- 2024–2025: Ohio launched adult-use sales (2024), Delaware launched retail sales (August 2025), Kentucky launched its medical program (January 2025), Texas expanded its limited medical program (September 2025)
- April 2026: The DOJ placed state-licensed medical marijuana in Schedule III, the most significant federal reclassification since 1970
As of early 2026, 24 states, DC, Guam, and the Northern Mariana Islands have adult-use recreational legalization; 40+ states, DC, Puerto Rico, and Guam have some form of medical marijuana program. An estimated 64.2 million people 12 and older in the US used cannabis in the past year in 2024, with 15.4% past-month use, up from 6.1% in 2008.
What Legalization Has Produced: Public Health Implications
The public health effects of marijuana legalization have been actively studied since 2012, with a growing body of evidence. The picture is complex:
Cannabis use increased in adults but not uniformly in adolescents. Legal adult-use states have seen increases in cannabis use among adults, consistent with reduced barriers to access. The impact on adolescent use has been more variable; some studies show no significant increase, others show modest increases in states with recreational markets, and national surveys show increasing teen use in the overall context of widespread state-level access changes. The research is ongoing.
Risk perception declined. One of the most consistently documented effects of legalization is a decline in perceived risk of cannabis use, particularly among youth. This is a public health concern because reduced perceived risk predicts increased use, including escalation in vulnerable populations.
Cannabis use disorder rates have increased. As cannabis use has grown, so has the total number of people meeting criteria for cannabis use disorder. According to the 2023 National Survey on Drug Use and Health, approximately 19.2 million people met past-year CUD criteria, up from earlier estimates. Daily and near-daily use, the primary driver of CUD, has also increased significantly since 2015, alongside the proliferation of higher-potency products in legal markets.
Illicit market persistence. Legal markets have not fully displaced illicit cannabis markets in most states. Price differentials (legal cannabis is taxed and often more expensive), regulatory burdens on small cultivators, and geographic access gaps maintain illicit supply. The illicit market is a regulatory failure: unregulated potency, no age verification, and no consumption messaging.
Emergency department and poison control trends. Cannabis-related ED visits and poison control calls have increased in legal states, particularly involving unintentional pediatric ingestion of edibles. The edible products that make cannabis more accessible and palatable for adults also create pediatric poisoning risks that child-resistant packaging has only partially mitigated.
Traffic safety. Cannabis-impaired driving is a serious public health concern in legal states. Roadside detection of cannabis impairment is substantially more difficult than alcohol (no equivalent of the breathalyzer for THC). Studies of traffic fatalities post-legalization show mixed results across states, but the concern is real and the policy response is underdeveloped.
Social equity outcomes. One of the central justifications for legalization was addressing the racial inequity of cannabis enforcement. Legal states have had mixed success on equity provisions. Arrest disparities have reduced in most legal states, though not eliminated. Social equity licensing programs designed to prioritize historically impacted communities have faced implementation challenges including capital access barriers and regulatory delays that have often disadvantaged the equity applicants they were designed to help.
Potency as a Public Health Variable
One dimension of legalization that has not received adequate public health attention is the dramatic escalation of cannabis potency in legal markets. Average THC content in legal market flower products has exceeded 20% in many states, several times the average potency in products studied in the clinical literature. Concentrates available in legal dispensaries routinely test at 50–90% THC. This product evolution means that the harms documented in research from lower-potency products are likely underestimates of the harms from current legal market products.
Professional Perspective
The concerns about legalization that run through addiction treatment circles don’t come only from prohibitionists. Roger A. Roffman spent decades studying marijuana dependence interventions and worked as an addictions therapist at the University of Washington School of Social Work. Writing in NCBI, he acknowledged the appeal of legalization arguments (social justice, tax revenue, failed prohibition) while laying out the public health concerns that still gave him pause.
“Legalization likely will convey an erroneous message that marijuana use has no risks, and with that belief, attitudes will likely change and the prevalence of use, adverse consequences as well, may rise. Those who have been protected from harm because of their anti-drug attitudes and the stigma attached to marijuana use, due in part to its illegality, will lose that protection.”
For people whose marijuana use has crossed into dependence or disorder, the normalization that legalization accelerates can make it harder to recognize a problem, and finding treatment is the first step toward addressing it.