The federal government first criminalized marijuana in the 1930s with the Marihuana Tax Act of 1937, and cannabis activity remains a federal crime today.
Modern federal marijuana law is codified under the Controlled Substances Act of 1970, which sought to update the Marihuana Tax Act. Since then, marijuana has remained a "Schedule I" controlled substance, meaning it sits at the top of the list of dangerous drugs alongside heroin and LSD, and that scientists deem it to have a high potential for abuse and no medical use.
Prohibition proponents have maintained cannabis as a high potential for abuse and no medical value. They allege cannabis is a "gateway drug" to harder drug use and that allowing cannabis encourages teen use of the drug.