Today is the 70th anniversary of the Marihuana Tax Act, which Franklin Roosevelt signed into law on August 2, 1937. Ostensibly a revenue measure, the act effectively banned marijuana by imposing prohibitive taxes and onerous requirements for legal possession. In 1970 (by which time Congress had stopped pretending to care about constitutional limits on its powers) the Controlled Substances Act banned marijuana directly, classifying it as a Schedule I drug along with heroin and LSD.
Fun fact: The year before Congress passed the CSA, psychedelic evangelist Timothy Leary persuaded the U.S. Supreme Court that the Marihuana Tax Act violated the Fifth Amendment's ban on compelled self-incrimination because it required even unregistered (and therefore illegal) possessors of cannabis to pay a "transfer tax." Leary was convicted of failing to pay the tax after he was caught at the U.S.-Mexican border with a small amount of pot (his daughter's, actually).
To give you an idea of how much thought Congress put into passing the first federal marijuana ban, here is an exchange that occurred when the bill came to the House floor on the night of June 10, 1937 (emphasis added):
Rep. Robert L. Doughton (D-N.C.): I ask unanimous consent for the present consideration of the bill (H.R. 6906) to impose an occupational excise tax upon certain dealers in marihuana, to impose a transfer tax upon certain dealings in marihuana, and to safeguard the revenue therefrom by registry and recording.
Rep. Betrand Snell (R-N.Y.): Mr. Speaker, reserving the right to object, and notwithstanding the fact that my friend, Reed [Rep. Chauncey Reed (R-Ill.)], is in favor of it, is this a matter we should bring up at this late hour of the afternoon? I do not know anything about the bill. It may be all right and it may be that everyone is for it, but as a general principle, I am against bringing up any important legislation, and I suppose this is important, since it comes from the Ways and Means Committee, at this late hour of the day.
Rep. Sam Rayburn (D-Texas), future speaker of the House: Mr. Speaker, if the gentleman will yield, I may say that the gentleman from North Carolina has stated to me that this bill has a unanimous report from the committee and that there is no controversy about it.
Snell: What is the bill?
Rayburn: It has something to do with something that is called marihuana. I believe it is a narcotic of some kind.
Fred M. Vinson (D-Ky.), future chief justice of the U.S.: Marihuana is the same as hashish.
Snell: Mr. Speaker, I am not going to object, but I think it is wrong to consider legislation of this character at this time of night.
To the extent that members of Congress had heard of marijuana, they knew it as a drug that drove its users mad and caused them to commit horrendous crimes. Fortunately, we are much wiser today.
The Marijuana Policy Project's Rob Kampia sums up the achievement of the courageous legislators who didn't let their ignorance about cannabis prevent them from banning it:
Federal government estimates indicate that marijuana use has increased approximately 4,000 percent since the Marijuana Tax Act took effect. A study by researcher Jon Gettman, Ph.D., published in December 2006 and based on government data, found marijuana to be the country's number-one cash crop, exceeding the value of corn and wheat combined. The federally funded Monitoring the Future survey reports that approximately 85 percent of high school seniors describe marijuana as "easy to get"—a figure that has remained virtually unchanged since the survey began in 1975. In 2005 (the most recent figures available), U.S. law enforcement made an all-time record 786,545 marijuana arrests—89 percent for possession, not sale or trafficking.