The number 420 has become a euphemism for one's support for cannabis and drug culture in general. The exact origin of the term is unknown, although there is much speculation, and a large number of urban legends surrounding its origin. Although dedicated marijuana smokers partake at almost any time of day, smoking at 4:20 or on April 20 has special meaning to some. Punctual and exacting smokers smoke-out at 4:20 AM, insisting that 4:20 PM is actually 16:20 (24 hour time). Many of the clocks in the movie Pulp Fiction are set to 4:20. In an episode of the show Futurama, an alternate universe where everyone is a hippie is numbered as Universe 420.
An origin story according to Snopes and The Straight Dope claims that in the early 1970s a group of California teenagers at San Rafael High School used to meet every day to smoke marijuana after school at 4:20 PM. The time became a code word for the drug, and usage spread. 4:20 PM has since become a popular time to "smoke out." It's also worth noting that 4:20 PM is the time of LSD creator Albert Hofmann's first deliberate ingestion of the substance, in 1943 on what was latter dubbed Bicycle Day; perhaps this is where the San Rafael kids picked up the idea.
Another possible origin of the term can be found in the works of H. P. Lovecraft. A short story of his, entitled "In the Walls of Eryx" and first published in Weird Tales [34, No. 4 (October 1939), pp50-68], contains this passage:
I had encountered at least one of those curious mirage-plants about which so many of our men told stories. Anderson had warned me of them, and described their appearance very closely - the shaggy stalk, the spiky leaves, and the mottled blossoms whose gaseous dream-breeding exhalations penetrate every existing make of mask...Although everything was spinning perilously, I tried to start in the right direction and hack my way ahead. My route must have been far from straight, for it seemed hours before I was free of the mirage-plant's pervasive influence. Gradually the dancing lights began to disappear, and the shimmering spectral scenery began to assume the aspect of solidity. When I did get wholly clear I looked at my watch and was astonished to find that the time was only 4:20. Though eternities had seemed to pass, the whole experience could have consumed little more than a half-hour.
In 1955, Raj Kapoor directed a film entitled Shree 420 (Mr. 420), a reference to someone who has a reputation for theft and deception, since apprehensions for such crimes are usually section 420 of the Indian Penal Code.
Other theories include:
* The number is a police numeric code for a drug bust.
* There were, at one time, believed to be 420 chemicals in marijuana.
* April 20th, or 4-20, is the last day on which one is supposed to plant cannabis seeds.
* April 20th, or 4-20, is the birthday of Adolf Hitler.
* The Beatles song "Come Together" is 4:20 in length.
Today many people who smoke marijuana use 420 to symbolize their desire to smoke. In 1994, classified ads in the Santa Cruz Sentinel for "Housing to share" began reading as: "Rm avail Veggie household. 420. No pets M pref"