How Cannabis Was Prohibited: The War on Drugs

Cannabis prohibition is often presented as a public-health measure, but its origins had far more to do with politics, racism, and economics than with science. For most of American history, hemp was an ordinary crop, and cannabis preparations appeared openly in pharmacies. Within a few decades of the early 20th century, however, the plant was recast as a dangerous narcotic. Understanding how that happened — and whom it targeted — is essential to understanding the modern cannabis debate and its ongoing social consequences.

Before Prohibition: Cannabis as Medicine and Industry

In the 19th century, cannabis was a legitimate medicine in the United States and Europe. It appeared in the United States Pharmacopeia, and tinctures were widely sold in pharmacies. The Irish physician William Brooke O'Shaughnessy introduced cannabis to Western medicine in the 1840s after observing its use in India, and for decades it was prescribed for pain, muscle spasms, and other conditions.

Hemp, the fiber variety of the plant, was also a major industrial crop. It was grown for rope, sailcloth, and canvas across the American colonies and into the 19th century. There was no national stigma attached to cannabis — it was simply another medicine and fiber crop, used mostly in liquid form and unremarkable to most Americans.

Early 20th Century: The Mexican Revolution and Racist Association

The shift toward prohibition began in the 1910s, and it was driven by social panic more than pharmacology. During the Mexican Revolution of 1910, refugees and immigrants fled north into the United States, bringing with them the practice of smoking marihuana — the recreational use of the plant's flowers. While Americans already had cannabis tinctures in their medicine cabinets, the smoked form was new and culturally unfamiliar.

Newspapers and politicians began linking cannabis to Mexican immigrants, portraying it as a foreign vice that incited violence and madness. This was the period when the term "marihuana" (later "marijuana") displaced the older, neutral word "cannabis" in public discourse — a deliberate choice that made the plant sound foreign and threatening. Several states, starting with Massachusetts in 1911 and followed by Utah, Texas, and others through the 1910s and 1920s, banned the plant. These early laws were aimed overwhelmingly at controlling and criminalizing Mexican and Black communities.

Harry Anslinger and the Federal Bureau of Narcotics

The person most responsible for national prohibition was Harry J. Anslinger. Appointed to lead the new Federal Bureau of Narcotics in 1930, Anslinger initially dismissed cannabis as a minor concern. But after alcohol prohibition was repealed in 1933, he faced pressure to justify his agency's budget. He turned to cannabis and launched a relentless propaganda campaign.

Anslinger's rhetoric was openly racist. He collected and promoted sensational stories linking cannabis to crime, frequently invoking race — claiming the drug caused Black men to become violent and that it led white women into relationships with men of color. He testified before Congress with claims about cannabis-induced insanity and murder that had no scientific basis. His testimony was central to the political momentum for a federal ban.

"Reefer Madness" and the Marihuana Tax Act of 1937

The propaganda reached a cultural peak with the 1936 film Tell Your Children, later re-released and widely known as Reefer Madness. The film depicted casual cannabis use spiraling into hallucinations, insanity, and murder — claims that bear no resemblance to the actual effects of the drug. It became a touchstone of anti-cannabis messaging for decades.

In 1937, Anslinger's campaign culminated in the Marihuana Tax Act. Rather than banning cannabis outright, the law imposed a transfer tax and a maze of regulatory requirements that effectively made the plant impossible to sell or prescribe legally. The American Medical Association opposed the law, arguing there was no medical reason to restrict cannabis, but it passed anyway. The first person arrested under the Act, Samuel Caldwell, was sentenced to four years of hard labor for selling two joints — a punishment that set the tone for decades of enforcement.

The UN Single Convention and Global Export

U.S. prohibition went global in 1961 with the United Nations Single Convention on Narcotic Drugs. This treaty placed cannabis alongside heroin and cocaine as a dangerous drug with no medical value and required member states to restrict it heavily. Because the United States drove much of the treaty's content, American prohibition attitudes effectively shaped international drug policy for the rest of the 20th century.

The Single Convention remains in force today and is one reason so many countries still classify cannabis strictly. Reforming it is a slow diplomatic process, which is why even pro-legalization nations sometimes frame their laws around "medical" or "tolerance" models rather than full legalization.

Nixon, the Controlled Substances Act, and the "War on Drugs"

In 1970, President Richard Nixon signed the Controlled Substances Act, which created the scheduling system still used today. Cannabis was placed in Schedule I — the most restrictive category, reserved for drugs with "high potential for abuse" and "no accepted medical use." Heroin and LSD share that tier; cocaine and methamphetamine are actually classified one tier lower (Schedule II), which is scientifically indefensible and reveals how political the scheduling was.

In 1971, Nixon officially declared a "War on Drugs," framing drug use as a law-enforcement problem rather than a public-health one. Decades of subsequent research, including reporting on the Nixon administration's own internal deliberations, have made clear that the war on drugs was politically motivated. A 2016 quote widely attributed to Nixon aide John Ehrlichman described targeting anti-war protesters and Black Americans through drug enforcement — an admission that, regardless of exact phrasing, aligns with the policy's clear effects.

Disproportionate Enforcement

The practical result of the War on Drugs was mass incarceration that fell overwhelmingly on Black and Latino communities. Despite surveys consistently showing that cannabis use rates are similar across racial groups, Black Americans have historically been arrested for cannabis possession at several times the rate of white Americans. This disparity fueled decades of lost jobs, broken families, and deep distrust of the criminal justice system.

The legacy persists even as legalization spreads. People still sit in prison for conduct that is now legal in many states, and expungement of past convictions has been slow and uneven. Modern legalization efforts increasingly include social-equity provisions aimed at repairing some of this damage.

Key takeaways

• Cannabis was legal medicine for most of U.S. history — it appeared in the Pharmacopeia and was sold openly in pharmacies until the 1930s.
• Early state bans were rooted in racism, targeting Mexican immigrants and Black communities rather than any new scientific finding.
• Harry Anslinger engineered federal prohibition through sensational, scientifically unsupported propaganda to justify his agency's existence.
• The 1937 Marihuana Tax Act effectively criminalized cannabis; the 1970 Controlled Substances Act made it Schedule I.
• The War on Drugs was politically motivated, with enforcement falling disproportionately on Black and Latino Americans.
• U.S. policy was exported globally through the 1961 UN Single Convention on Narcotic Drugs.

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