The federal law that makes possession of marijuana a crime has its origins in legislation that was passed in an atmosphere of hysteria during the 1930s and that was firmly rooted in prejudices against Mexican immigrants and African-Americans, who were associated with marijuana use at the time. This racially freighted history lives on in current federal policy, which is so driven by myth and propaganda that it is almost impervious to reason.

The cannabis plant, also known as hemp, was widely grown in the United States for use in fabric during the mid-19th century. The practice of smoking it appeared in Texas border towns around 1900, brought by Mexican immigrants who cultivated cannabis as an intoxicant and for medicinal purposes as they had done at home.

Within 15 years or so, it was plentiful along the Texas border and was advertised openly at grocery markets and drugstores, some of which shipped small packets by mail to customers in other states.

The law enforcement view of marijuana was indelibly shaped by the fact that it was initially connected to brown people from Mexico and subsequently with black and poor communities in this country. Police in Texas border towns demonized the plant in racial terms as the drug of “immoral” populations who were promptly labeled “fiends.”

As the legal scholars Richard Bonnie and Charles Whitebread explain in their authoritative history, “The Marihuana Conviction,” the drug’s popularity among minorities and other groups practically ensured that it would be classified as a “narcotic,” attributed with addictive qualities it did not have, and set alongside far more dangerous drugs like heroin and morphine.

By the early 1930s, more than 30 states had prohibited the use of marijuana for nonmedical purposes. The federal push was yet to come.

The stage for federal suppression of marijuana was set in New Orleans, where a prominent doctor blamed “muggle-heads” — as pot smokers were called — for an outbreak of robberies. The city was awash in sensationalistic newspaper articles that depicted pushers hovering by the schoolhouse door turning children into “addicts.” These stories popularized spurious notions about the drug that lingered for decades. Law enforcement officials, too, trafficked in the “assassin” theory, under in which killers were said to have smoked cannabis to ready themselves for murder and mayhem.