How 4/20 Became a Date Synonymous With Cannabis

Published: 8 April 2026
Last Updated: 27 July 2026
Last Reviewed: 27 July 2026
Author: Weed Supermarket Editorial Team

A UK Guide

Every year on 20 April, people around the world recognise 4/20 as a date associated with cannabis culture, political campaigning and discussions about drug policy.

What began as a private code used by a small group of Californian students eventually spread through music communities, magazines and international popular culture. In the UK, 4/20 gatherings have also become associated with campaigns to reform cannabis laws.

This guide explores the most widely accepted origin of 420, how April 20 became an international date and what 4/20 means within the current UK legal landscape.

What Does 420 Mean?

The term “420” is widely used as shorthand for cannabis. It may refer to:

The time 4:20pm.
The date 20 April, written in the American format as 4/20.
Cannabis culture more generally.
Events and campaigns associated with cannabis-law reform.

Although several alternative explanations have circulated over the years, the most widely documented origin involves a group of students at San Rafael High School in California during 1971.

Who Were the Waldos?

The Waldos were a group of five friends who attended San Rafael High School in Marin County, California.

The group reportedly received information about an abandoned cannabis crop and agreed to meet after school to search for it.

They chose 4:20pm as their meeting time because school activities had finished by then. Their original phrase, “4:20 Louis”, referred to both the time and a meeting place near a statue of Louis Pasteur on the school grounds.

Although the group did not find the alleged crop, “420” remained part of their private vocabulary and developed into a general code for cannabis.

Common Myths About the Origin of 420

Several alternative explanations have been repeated online, but there is limited evidence supporting them.

Common myths include claims that 420 was:

A police radio code for cannabis possession.
The number of active chemicals in cannabis.
A reference to Bob Dylan lyrics.
Connected to a specific section of Californian criminal law.
The date of a famous musician’s death.

The Waldos’ account is generally regarded as the best-supported origin because it is associated with surviving correspondence, photographs and contemporary connections.

How Did 420 Spread Beyond California?

The term remained relatively local until it began circulating within the community surrounding the Grateful Dead.

The Waldos had personal connections to people associated with the band, whose concerts attracted a large travelling fan community commonly known as Deadheads.

As the expression moved through this network, it became familiar to people outside Marin County and was increasingly used as shorthand for cannabis.

The Role of the Grateful Dead Community

The Grateful Dead were closely associated with the counterculture that developed around San Francisco during the 1960s and 1970s.

The band’s large touring community provided an effective way for slang, ideas and cultural references to spread across the United States.

By the late 1980s and early 1990s, “420” had moved well beyond the Waldos’ original friendship group and was becoming part of wider cannabis culture.

How High Times Helped Popularise 420

A major stage in the term’s development came when a flyer promoting a cannabis gathering at 4:20pm on April 20 reached a reporter connected with High Times magazine.

The magazine subsequently published references to 420, helping introduce the term to a much larger international readership.

During the 1990s, 420 became increasingly visible through:

Cannabis magazines.
Music festivals.
Countercultural events.
Clothing and merchandise.
Internet forums.

The date 20 April then developed into an informal annual event rather than simply a reference to a time of day.

How April 20 Became an International Cannabis Date

As awareness grew, gatherings began taking place at 4:20pm on April 20 in cities around the world.

These events vary significantly. Some are primarily cultural or social, while others are organised as political demonstrations calling for changes to cannabis legislation.

In jurisdictions with regulated adult-use markets, 4/20 may also involve licensed events, educational campaigns and commercial promotions.

In countries where recreational cannabis remains illegal, public gatherings can create legal and public-safety issues.

The Growth of 4/20 in the UK

The expression reached UK audiences through music, magazines, films, television and the internet.

By the early 2000s, public gatherings connected with April 20 had become increasingly visible in Britain.

Events have taken place in cities including:

London.
Brighton.
Bristol.
Manchester.
Glasgow.

Attendance, organisation and police responses have varied from year to year.

Why Is Hyde Park Associated With 4/20?

Hyde Park in central London has become the best-known location for UK 4/20 gatherings.

Large numbers of people have attended in previous years to socialise, discuss cannabis policy and participate in demonstrations supporting legal reform.

However, these gatherings do not create an exemption from UK drug laws or Royal Parks regulations.

Police may attend, and individuals can still face enforcement action for possession, supply or other offences.

Is 4/20 an Official UK Event?

There is no official national cannabis holiday in the United Kingdom.

Individual gatherings may be organised informally or promoted by campaign groups, but their existence does not mean they have been authorised by the police, local authority or Royal Parks.

Anyone attending a public event remains responsible for complying with the law and any rules applying to the location.

Current Cannabis Law in the UK

Cannabis remains a Class B controlled drug under the Misuse of Drugs Act 1971.

Without a relevant legal exemption, it is illegal to:

Possess cannabis.
Produce or cultivate cannabis.
Supply cannabis.
Import or export cannabis.

Penalties vary according to the offence and circumstances. Possession can carry a maximum penalty of five years’ imprisonment, an unlimited fine or both. Supply and production can carry substantially higher penalties.

Medical Cannabis in the UK

Since November 2018, specialist doctors have been able to prescribe certain cannabis-based medicinal products in limited circumstances.

This change did not legalise recreational cannabis.

Medical cannabis access involves clinical assessment, a specialist prescribing decision and supply through an authorised pharmacy or dispensing arrangement.

It should not be confused with purchasing cannabis from an ordinary website, social media account or public event.

What Does 4/20 Represent in the UK?

Different people interpret the date in different ways.

For some, 4/20 represents:

Cannabis culture and shared identity.
Campaigning for legal reform.
Medical cannabis awareness.
Harm-reduction education.
Discussion about policing and criminal justice.
Opposition to prohibition.

For others, the date raises concerns about public drug use, youth exposure, health risks and the enforcement of existing law.

A balanced discussion should recognise both the cultural importance of the date and the public-policy questions surrounding it.

4/20 and Cannabis-Law Reform

Campaigners have used April 20 to call for changes including:

Decriminalisation of personal possession.
A regulated adult-use market.
Wider access to prescribed cannabis-based medicines.
Expungement of some historical convictions.
A greater emphasis on public health and harm reduction.

Opponents of reform commonly raise concerns about high-potency products, dependence, mental health, road safety and potential youth access.

Any change to UK cannabis law would require political and parliamentary action. Public gatherings do not themselves alter the legal position.

How 4/20 Has Changed in Legal Cannabis Markets

In parts of North America where adult-use cannabis has been legalised, 4/20 has developed into a mixture of cultural event, political anniversary and commercial occasion.

Licensed businesses may hold promotions, while public-health bodies use the date to communicate information about responsible use, impaired driving and product safety.

This commercialisation has created debate within cannabis communities. Some people welcome the wider acceptance of cannabis, while others believe the original countercultural and political meaning of 420 has been diluted.

4/20 and Social Media

Social media has accelerated the international spread of 4/20 culture.

Hashtags, videos, memes and live broadcasts allow events in one country to reach audiences worldwide almost instantly.

However, social platforms can also expose users to:

Illegal sellers.
Fraudulent cannabis websites.
Fake competitions.
Counterfeit products.
Misleading medical claims.

People searching for 4/20 offers or cannabis products should remain cautious, particularly when approached by anonymous sellers through Telegram, WhatsApp, Instagram or Snapchat.

4/20 Cannabis Scams

Fraudsters may exploit increased search interest around April 20 by advertising limited-time offers, festival stock or guaranteed cannabis delivery.

Common warning signs include:

High-THC cannabis openly offered for nationwide UK delivery.
Pressure to pay before an alleged 4/20 deadline.
Cryptocurrency-only payments.
Requests for gift cards or vouchers.
Additional courier or insurance fees after payment.
New websites with no verifiable history.
Anonymous social media or messaging-app accounts.

Read our Cannabis Scams UK guide before sending money to an unfamiliar seller.

Buying Cannabis Online in the UK

There is currently no regulated recreational online cannabis market in the United Kingdom.

Websites openly offering unrestricted high-THC cannabis for general UK delivery may be operating illegally, fraudulently or both.

Legal routes and product categories are different:

Prescription cannabis-based medicinal products may be supplied through authorised pharmacies following specialist assessment.
Some hemp-derived cannabinoid products may be sold online when they comply with applicable UK requirements.

A product should not be assumed to be lawful simply because it is described as CBD, hemp, THCa or a legal alternative.

Legal Hemp-Derived Cannabinoid Products

Depending on their composition, intended category and regulatory status, online retailers may offer products containing cannabinoids such as CBD and CBG.

Possible formats include:

CBD and CBG isolates.
Cannabinoid extracts.
Herbal cannabinoid products.
Solid or hash-style cannabinoid products.

Consumers should look for clear product information, laboratory reports and published compliance procedures.

Learn more in our UK Compliance & Laboratory Testing guide.

How to Mark 4/20 Responsibly

People interested in 4/20 can engage with the date without possessing or using illegal substances.

Activities may include:

Learning about cannabis history.
Reading evidence-based research.
Watching policy debates.
Exploring the history of hemp.
Following lawful political campaigns.
Discussing medical cannabis access.
Learning how to recognise online scams.

Educational participation allows people to understand the cultural and political significance of 4/20 while remaining aware of current UK law.

Related Guides

Frequently Asked Questions

What does 420 mean?

420 is a widely recognised term associated with cannabis. It originated as a code used by a group of Californian students who arranged to meet at 4:20pm.

Why is April 20 called 4/20?

In the American date format, April 20 is written as 4/20. As the number 420 became associated with cannabis, the corresponding date developed into an annual cultural event.

Who invented the term 420?

The most widely accepted account credits five students from San Rafael High School in California known as the Waldos.

Is 420 a police code for cannabis?

There is no reliable evidence that the term originated as a police radio code. This is one of several myths surrounding its history.

Why is Hyde Park associated with 4/20?

Hyde Park has become the best-known location for annual UK 4/20 gatherings involving cannabis culture and calls for legal reform.

Is the Hyde Park 4/20 gathering legal?

The gathering does not create an exemption from UK drug laws or park regulations. Police may take enforcement action where offences occur.

Is recreational cannabis legal in the UK?

No. Cannabis remains a Class B controlled drug unless a specific legal exemption applies.

Can medical cannabis be prescribed in the UK?

Yes. Certain cannabis-based medicinal products may be prescribed by specialist clinicians in limited circumstances.

Can you legally order recreational cannabis online in the UK?

No regulated recreational online cannabis market currently exists in the UK.

Why do cannabis campaigners use 4/20?

The date provides a widely recognised opportunity to discuss legal reform, medical access, criminal justice and harm reduction.

Final Thoughts

What began as a private meeting time used by five Californian students has developed into one of the most recognisable symbols in international cannabis culture.

The expression spread through the Grateful Dead community, gained wider attention through cannabis media and eventually transformed April 20 into an annual date observed around the world.

In the UK, 4/20 combines cultural identity with political debate. Gatherings such as those associated with Hyde Park draw attention to cannabis law, medical access and public attitudes, but they do not change the current legal position.

Understanding the history of 420 provides useful context for modern discussions about cannabis, regulation and the continuing evolution of public policy.

Compliance Statement

This article is provided for historical, cultural, legal-awareness and educational purposes only. It does not encourage the purchase, possession, supply or use of illegal controlled substances. Cannabis remains controlled under UK law except where a specific legal exemption applies. References to 4/20 gatherings do not imply that public cannabis possession or use is lawful. This content does not constitute legal or medical advice.