Weed Day

1. The unofficial celebration dedicated to marijuana.
2. 420, 4:20, or 4/20 (pronounced four-twenty) is a code-term in cannabis culture that refers to the consumption of cannabis, especially smoking cannabis around the time 4:20 p.m./a.m. (or 16:20 in 24-hour notation) and smoking and celebrating cannabis on the date April 20 (which is 4/20 in U.S. form).
3. There are a few possible explanations for why marijuana enthusiasts' day of celebration landed on April 20, but the real origin remains a bit of a mystery.
4. Steven Hager, a former editor of the marijuana-focused news outlet High Times, told the New York Times that the holiday came out of a ritual started by a group of high school students in the 1970s. As Hager explained, a group of Californian teenagers ritualistically smoked marijuana every day at 4:20 pm. The ritual spread, and soon 420 became code for smoking marijuana. Eventually 420 was converted into 4/20 for calendar purposes, and the day of celebration was born. (A group of Californians published documents giving this theory legitimacy, but it's unclear if their claims are valid.)
5. One common belief is that 420 was the California police or penal code for marijuana, but there's no evidence to support those claims.
6. Another theory is that there are 420 active chemicals in marijuana, hence an obvious connection between the drug and the number. But there are more than 500 active ingredients in marijuana, and only about 70 or so are cannabinoids unique to the plant, according to the Dutch Association for Legal Cannabis and Its Constituents as Medicine.
7. A lesser-known possibility comes from the 1939 short story "In the Walls of Eryx" by H.P. Lovecraft and Kenneth Sterling. The story describes "curious mirage-plants" that seemed fairly similar to marijuana and appeared to get the narrator high at, according to his watch, around 4:20. Since the story is from 1939, it's perhaps the earliest written link between marijuana and 420.
8. Festivities are widespread in the US, where observances have been held in locations including Hippie Hill in Golden Gate Park, San Francisco and Parliament Hill in Ontario.
9. Today, it remains a term used to describe the consumption of weed, especially at around 4:20pm in the afternoon.
10. Medical marijuana is legal in many parts of the US, with recreational use of the drug also allowed in certain states such as Alaska, California and Colorado.
11. Most cannabis smokers report feeling relaxed, giggly and hungry, although some can feel light-headed, faint and sick. In some cases the drug may cause feelings of anxiety, suspicion, panic and paranoia.
12. Last November 2017, California voted "yes" to legalizing recreational marijuana, making this week's annual celebration of marijuana in San Francisco the first officially sanctioned event by the city. A bevvy of sponsors were on hand to demonstrate the weed economy's growing clout, including HEMP20, Green Door SF and High Times Magazine (naturally). 

References:

http://www.express.co.uk/news/uk/794153/420-meaning-weed-day-what-is-cannabis-marijuana

https://www.vox.com/2014/4/19/5624560/why-is-420-national-weed-day

https://www.thesun.co.uk/living/3352744/420-day-cannabis-marijuana-april-20-weed/

http://www.huffingtonpost.com/2012/04/20/april-20-weed-day_n_1440522.html

http://www.huffingtonpost.com/2012/04/20/420-weed-day-marijuana-april-holiday_n_1437964.html

https://en.wikipedia.org/wiki/420_(cannabis_culture)

http://www.cnbc.com/2017/04/22/how-san-francisco-celebrated-the-first-official-weed-day-this-week.html