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The History of 4/20: A THC Cannabis 'Holiday'

Updated: Aug 2, 2022

As 4/20 quickly approaches, we explore the history of this THC cannabis “holiday” and highlight a brief timeline on the plant’s history.

One of many slang terms for THC cannabis use is “four-twenty.” Although there are a number of urban legends, the term “420” is widely believed to have come from a group of five high school students in California who met each afternoon at 4:20 p.m. to search for an abandoned cannabis crop (and to partake).

Although the teenagers never found the crop, they used “4:20” as a code-word to refer to cannabis consumption. The term seems to have caught on after Dave Reddix, one of the five, became a roadie for the Grateful Dead and the band’s followers, at least, in part, popularized the lingo.

Over the years, April 20th – or 4/20—became an international counterculture holiday. On this date, people gather, frequently at 4:20 p.m., to use cannabis and sometimes to advocate for its legalization.

4/20 in the Broader Culture

Observances of 4/20 are international and have popped up everywhere from Washington Square Park in New York City to Golden Gate Park in San Francisco. Outside the US, 420 events have been held in Vancouver, Montreal, Melbourne, Sydney, and London, as well as in New Zealand, Slovenia, and even northern Cyprus.

The popularity of 4/20 as a holiday and as a slang term has seeped into the broader culture. In 2016 HarperCollins published The 420 Gourmet, a cookbook billed as “the foodie’s guide to cannabis.”

As another sign of the spread of this inside joke, highway signs with the number “420” have frequently been stolen, presumably by cannabis enthusiasts. To thwart the thefts, Colorado’s transportation department replaced its 420-mile marker with one that read “419.99.” When word spread of this creative solution, the 419.99 sign was stolen, too, and the site of the marker has become a mecca for cannabis enthusiasts and tourists drawn to offbeat attractions.

Nods to “420” are increasingly mainstream. For instance, in 2014, after some types of cannabis possession were legalized in Washington, DC, Mayor Muriel Bowser granted license plate number 420 to Adam Eidinger, who headed up the DC Cannabis Campaign, according to an article in the Washington Post.

A Timeline

In honor of 4/20, here is a brief – and admittedly impressionistic-- history of cannabis over the past 5,000 years:

2900 BC. Cannabis is identified as a popular medicine by Chinese Emperor Fu Hsi.

70 AD. Roman medical texts refer to cannabis as a cure for ear pain and a way to suppress sexual desire.

1765. In his journals, George Washington discusses the potential of THC cannabis as a medicine.

1862. A candy made from hashish is advertised in Vanity Fair; the candy is purported to cure melancholy and nervousness.

1906. The Food and Drug Act mandates that any product containing cannabis be labeled appropriately.

1911. Massachusetts becomes the first state to ban cannabis.

1936. By this date, all US states have some type of law regulating THC cannabis usage on their books. This is also the year in which the film Reefer Madness is released.

1952. The Boggs Act is passed, establishing mandatory sentences for drug convictions. The minimum sentence for THC cannabis possession is two-to-ten years, with a fine of up to $20,000.

1970. THC cannabis is classified as a S