There has never been a single defining reason why marijuana prohibition was implemented and lasted for so long. Some feel that cannabis prohibition was racially motivated; an over-reaction to Mexican and African-American culture, musicians and lifestyle. Others claim the roots of cannabis prohibition are to be found in political lethargy, opposition from alcohol/pharmaceutical corporate interests or a misplaced sense of moral/ethical protection to society.
But we do know that in early 1900, as America’s international influence was gathering momentum, a mixture of political, moral and ethical restrictions began to grow in influence. ‘Dry’ crusaders were already hard at work to prohibit alcohol. Presenting it as a victory for health and families. In 1918 the Wartime Prohibition Act was passed, banning drinks with over 1.28% alcohol. Eventually, and with support from other states, the 18th Amendment was passed banning alcohol on Jan 17th, 1920. The moral movement had set the scene and won. Alcohol was finally banned . Cannabis was viewed with equal (or even greater) suspicion and was next under the microscope of morality.
Numerous states had justified and implemented anti-cannabis laws in the 1920s. They listed marijuana as a poison to make their point crystal clear to the general public even though the new laws had required no scientific proof. States including Iowa, Nevada, Oregon, Washington, Arkansas, Nebraska, Louisiana, and Colorado all passed anti-poison legislation. Thirty additional states had cannabis-prohibition legislation waiting to be passed by the time alcohol prohibition was repealed in 1933.
Alcohol had sufficient popular support to be reclaimed as legal, but cannabis had no such luck and was destined to spend around a century languishing as an illegal drug even though it is less damaging than alcohol/tobacco and had important medical properties.
There were important industrial reasons why cannabis and hemp were regarded with corporate and social suspicion. Media baron William Randolph Hearst and Harry Anslinger (America’s first ‘drug czar’) quickly identified cannabis as the next social evil worthy of prohibition. Andrew Mellon, the US Treasury Secretary, was Anslinger’s boss and also uncle to his wife. Mellon also had links to Mellon Bank, a financial supporter of the DuPont company which created a line of man-made
paper to compete with paper made from Hemp. There were good financial and business reasons to ban cannabis/hemp-derived paper products and focus on new industrial paper production.
It’s worth adding that some cannabis historians feel that the commercial battles between modern paper and hemp-paper have been overstated and that racism and the desire for cultural control were the main motivation for cannabis prohibition
Cannabis first felt restrictions as early as 1860 in New York, however, the first serious anti-cannabis laws began to appear at USA state level in the 1910’s and 1920’s. Elsewhere in the world, there wasn't a similar concerted anti-cannabis campaign. In 1925, the USA supported the classification of ‘indian hemp’ as a drug at the International Opium Convention
Harry Anslinger was not at his most active as an anti-cannabis campaigner until the end of alcohol prohibition. Some attribute Anslingers enthusiasm for cannabis prohibition to the impending redundancy of his department as alcohol was being re-legalized. Medical testimony for the various medical uses of cannabis was ignored. Likewise, Anslinger ignored the American Medical Association’s evidence in which 29 of 30 pharmacists and drug industry representatives objected to his proposals to ban marijuana.
Anslinger was firmly established in his role to protect the public, and especially the young, from cannabis. He was active in the TV, radio, and newspaper. His work established plenty of fear, uncertainty, and doubt in the minds of the public.
As momentum gathered around marijuana prohibition, the mainstream media became the chief way for the anti-cannabis message to be delivered to the public. The movie ‘Reefer Madness’ was an infamous movie used to highlight the irrational hysteria which accompanied cannabis, especially during the early years. The content from Reefer Madness is regarded as laughable in the modern world, but in the early years of cannabis prohibition the message was taken with deadly seriousness and set the tone for decades of cannabis prohibition.
The following comes from Reefer Madness
“By the tons, it is coming into this country — the deadly, dreadful poison that racks and tears not only the body but the very heart and soul of every human being who once becomes a slave to it in any of its cruel and devastating forms.... Marihuana is a short cut to the insane asylum. Smoke marihuana cigarettes for a month and what was once your brain will be nothing but a storehouse of horrid specters. Hasheesh makes a murderer who kills for the love of killing out of the mildest mannered man who ever laughed at the idea that any habit could ever get him….” 
With the media successfully enrolled as a willing partner in the deliberate misinformation campaign (with support from sensationalist publisher William Randolph Hearst), Anslinger pushed the anti-cannabis movement from a state concern to a national crisis. Anslinger collected, created and used what he called his "Gore Files" . These were quotes from police reports used to portray offenses caused by drug users in the worst possible light. The Gore Reports were written in the bleak language of a police report. His most infamous story was that of Victor Licata who killed his family. This incident, said Anslinger, was precisely the type of thing that happened after cannabis was consumed. And without marijuana prohibition, more of this insanity was guaranteed;
“An entire family was murdered by a youthful addict in Florida. When officers arrived at the home, they found the youth staggering about in a human slaughterhouse. With an axe, he had killed his father, mother, two brothers, and a sister. He seemed to be in a daze... He had no recollection of having committed the multiple crimes. The officers knew him ordinarily as a sane, rather quiet young man; now he was pitifully crazed”
Cannabis prohibition had its origins in the early 20th century USA. Struggles with political, moral and racial influences played a large role. But things started to change in the 1960’s and 70’s as recreational cannabis consumption began. And this time there was nothing that could be done to prevent the widespread use of cannabis especially amongst the young, educated and liberated. President Reagan had his ‘Just Say No’ campaign which often linked cannabis use to harder drugs. But in 1996, Proposition 215 law was passed allowing the use of cannabis for medical reasons in California. Public trust in the Government led anti-cannabis message was now starting to disintegrate. Slowly but surely, momentum switched. Nowadays most of the USA has legalized cannabis and the same trends are starting to appear in other countries.
Cannabis prohibition continues to lose credibility and momentum each year. Cannabis laws are being changed rapidly, and medical cannabis use is one of the main factors necessitating changes to the law. Countries like South Africa, Australia, New Zealand, European nations, Canada, USA, and South American countries are all moving towards legal medical (and in some cases, recreational) use. The history of the prohibition of cannabis is long and complicated, many factors have influenced prohibition. However, after around a century of prohibition, we are finally able to say that the end of cannabis prohibition is finally in sight.
October 19th 2018