From the Document: "The Controlled Substances Act (CSA) places various substances in one of five schedules based on their medical use, potential for abuse, and safety or risk for dependence. The five schedules are progressively ordered with Schedule V substances regarded as the least dangerous and addictive and Schedule I substances considered the most dangerous and addictive. Schedule I substances are considered to have a 'high potential for abuse' with 'no currently accepted medical use in treatment in the United States.' [...] Marijuana is listed as a Schedule I controlled substance under the CSA, and has been on Schedule I since the CSA was enacted in 1970 (P.L. 91-513). [...] The Schedule I status of marijuana means that the substance is strictly regulated by federal authorities. Yet, over the last several decades, most states and territories have deviated from across-the-board prohibition of marijuana, and now have laws and policies allowing for some cultivation, sale, distribution, and possession of marijuana."
CRS Insight, IN11204
Congressional Research Service: https://crsreports.congress.gov/