The Origins of 420

420 is cannabis culture’s code for marijuana, and April 20 has become an unofficial cannabis holiday: a 2023 study found that medical dispensary transactions in Arizona rose sharply during the 4/20 week. The origin story told most often, which we could not confirm in an official record, points to a group of San Rafael, California high schoolers in 1971.

The number is also a time of day: 4:20, morning or afternoon. If you’re going to smoke cannabis, that’s the customary time.

Why? Because it’s tradition.

In fact, April 20 (4/20) is an unofficial holiday for marijuana consumers, medical and recreational alike. The banks may still be open and you still have to go to work, but that doesn’t make the day any less special.

Think we’re exaggerating when we call it “special”? We’re not. Dispensaries notice it too: in the Arizona study, medical cannabis sold rose by an average of 120.3 pounds a day during the 4/20 week. Florida treatment centers must post their prices and any discount policies online, so check those pages before you shop around April 20.

But what are the origins of 420? How did it become such a huge part of cannabis culture? Why not some other set of numbers, any set at all?

Some people claim that “420” comes from a numerological sequence that ancient Chinese healers used when they wrote about medicinal plants.

That claim comes with no source, which is a good reason to check what you read against the original source. Cannabis was used as medicine in ancient Asia, mainly in India.

But a lot of myths surrounding the origins of 420 have popped up over the years, and they are no better supported than the one you just read. Here are just a few of them.

What Are the Myths About Where 420 Came From?

• 420 is a police code for “marijuana.” No source supports this, and police radio codes differ from one agency to the next.

• Jimi Hendrix, Janis Joplin and Jim Morrison died on 4/20. Actually, Hendrix died on 9/18, Joplin died on 10/4 (which in many radio codes means “OK”) and Morrison died on 7/3. If you’re still looking for a common thread that connects these three musicians, here’s one: all three of them died at the age of 27.

• 4/20 is Adolf Hitler’s birthday. Yes, this is true, but it has nothing to do with the origins of 420 in cannabis culture. It’s just an unfortunate coincidence.

• April 20 is the perfect date to plant a marijuana crop. Nope. Planting dates depend on climate, and in Florida, home growing is not allowed, even for medical patients.

• It’s from the Bob Dylan song “Rainy Day Women #12 & 35”. This song talks a lot about getting stoned. And 12 multiplied by 35 equals 420, but that is only a coincidence.  Nothing to do with 420 as we know it.

• When the Grateful Dead stayed in hotel rooms, they always picked Room #420. No, but this is a little closer to the truth.  Maybe it’s the closest of all the myths out there.

Where Did 420 Come From?

As the story is usually told, a group of high schoolers in San Rafael, California created the code “420” as we know it in 1971. We could not confirm it in an official record, so treat the details below as the popular account.

These students called themselves “the Waldos.” No relation to the Where’s Waldo book series. They named themselves that because they literally hung out near a wall.

One fateful day, the Waldos found themselves in possession of a “marijuana treasure map.” The map supposedly led to a marijuana crop that was growing in Point Reyes, California.

The Waldos planned to get together after school to go find the crop. They got out of class at 3 pm, but some of them had after-school activities that lasted until 4 pm.

So they decided to meet at 4:20 pm. They’d get together, smoke some marijuana, and try to find this fabled cannabis crop.

They didn’t find the crop on their first outing. Or their second. Or their third.

In fact, they never found that crop. But they still kept meeting at 4:20 pm to go look for it.

From there, they started using “420” as a code for smoking marijuana in general, no matter what time it was. They used the code in school, right in front of teachers, and the teachers would have no idea what the Waldos were talking about.

Later, a family member of one of the Waldos was connected to Phil Lesh, bassist for the Grateful Dead, and the term “420” was passed on to the band. After that, the term began to spread.

By the usual account, in 1990 Oakland-based Deadheads distributed flyers inviting people to “smoke 420” on April 20, 4:20 pm. Somehow, one of the flyers ended up in the hands of High Times magazine. The magazine printed a copy of the flyer the following year and continued using 420 as a reference for marijuana.

From there the term spread through cannabis culture.

420 Today

“420” is now a staple of cannabis culture.

It’s constantly referenced in TV/films, magazines, websites, and products. Marijuana-related businesses incorporate it into their brand names. Some roommate ads on Craigslist make specific requests for “420-friendly” roommates.

It even made its way into state government. California’s 2003 Medical Marijuana Program law was Senate Bill 420, signed on October 12, 2003. Whether the number was picked on purpose has never been confirmed.

Why 4/20 Matters in Cannabis Culture

Cannabis has an interesting history of use on this planet. The ancients used it for many purposes, ranging from medicine to food to clothing to rope to religious sacrament. A 2006 review found it was used as medicine in Asia, mainly in India, before the Christian era.

In the United States, the Marihuana Tax Act of 1937 put it under federal regulation, and for decades it carried a heavy stigma.

Only in recent decades have states begun to allow medical use again.

We can’t think of any other plant, psychoactive or otherwise, that has its own holiday, and the Arizona sales figures show the day is a business event too. That just goes to show you the effect this plant has had on modern culture.

Holidays force us out of our normal routine and give us the opportunity to focus on the things that we too often take for granted. We at Dr. Green Relief are grateful to reside in a state that has legalized medical marijuana. By June 2022, 38 states and D.C. had legalized medical cannabis, a peer-reviewed study found, while the other 12 states had not.

So while April 20 is a day to celebrate medical marijuana with our patients, we also watch federal law: since April 28, 2026, marijuana subject to a state medical marijuana license is in Schedule III, but it is still a federally controlled substance. We hope the stigma keeps fading, so that patients feel free to tell their doctors about cannabis use, just as they would list any prescription or supplement.

But we’ll probably keep using the code “420.” After all, we’re still getting some good mileage out of it.

Last updated October 16, 2026 by the Dr. Green Relief Editorial Team.

Sources

• Meier MH, et al. The effects of the 4/20 cannabis holiday and adult-use cannabis legalization on medical cannabis sales and medical cannabis patient registration in Arizona. Int J Drug Policy. 2023 (PubMed)
• Zuardi AW. History of cannabis as a medicine: a review. Braz J Psychiatry. 2006 (PubMed)
• Steuart SR, et al. State Variation in U.S. Medical Cannabis Limits, Restrictions, and Therapeutic Cannabis Dosing. Cannabis. 2023 (PubMed Central)
• Federal Register, April 28, 2026, FR Doc. 2026-08176, Schedules of Controlled Substances: Rescheduling (govinfo, PDF)
• U.S. Customs and Border Protection. Did You Know… Marijuana Was Once a Legal Cross-Border Import?