Congress passes the Controlled Substances Act, placing marijuana in Schedule I

On October 27, 1970, President Richard Nixon signed the Comprehensive Drug Abuse Prevention and Control Act of 1970, Title II of which is the Controlled Substances Act (CSA). Taking effect on May 1, 1971, the law created the five-tier federal drug scheduling system still used in the United States today and placed cannabis (“marihuana”) and tetrahydrocannabinols in Schedule I.

Why Congress wrote a new federal drug law

For more than thirty years, federal cannabis enforcement relied on the Marihuana Tax Act of 1937, which did not technically ban cannabis outright but imposed steep transfer taxes and paperwork requirements. In May 1969, the U.S. Supreme Court unanimously struck down key enforcement provisions of the 1937 Act in Leary v. United States, ruling that forcing someone to register and pay the tax violated the Fifth Amendment protection against self-incrimination.

Rather than repairing the tax statute, Congress replaced it under the Commerce Clause with a unified system classifying drugs into five schedules based on medical utility and abuse potential.

What Schedule I meant for cannabis

Under the Controlled Substances Act, a Schedule I substance is defined by three criteria: a high potential for abuse, no currently accepted medical use in treatment in the United States, and a lack of accepted safety for use under medical supervision.

• Prohibition on prescriptions: Doctors could not prescribe Schedule I substances, and pharmacies could not dispense them.
• Research barriers: Scientists needed special DEA Schedule I registrations and had to source plant material through a single federally contracted facility at the University of Mississippi.
• The Shafer Commission: The 1970 Act created the National Commission on Marihuana and Drug Abuse (the Shafer Commission) to study where cannabis truly belonged. Although the Commission recommended in 1972 that personal possession be decriminalized, the Nixon administration rejected the findings and kept cannabis in Schedule I.

Why this date still matters

Every modern conflict between state and federal cannabis law—from dispensary banking and 280E tax penalties to interstate commerce bans and the 2023–2026 Schedule III rescheduling proceedings—traces directly back to the Schedule I placement enacted on October 27, 1970.