Cannabis

Cannabis is a plant genus, and a variety of psychoactive products derived from these plants, including marijuana and hashish. The plant also produces hemp fiber, and some extracts have medical uses but produce little or no intoxication.

There are two main chemicals within cannabis which produce its effects:

Tetrahydrocannabinol (THC) is the primary psychoactive chemical in cannabis which gives users the "high"
Cannabinoids (CBD) are non-psychoactive (so no "high") but instead offer pain relief, anxiety relaxation and potentially sleep improvements

Understand

The legality of cannabis varies between countries. In many countries usage and possession of any amount are illegal, and enforcement might be strict. Other countries criminalize cannabis trafficking, but do not punish users. In a few countries and territories, the whole production and consumption chain of cannabis is legal, in some for medical, in some also for recreational use.

Border controls on drugs are generally stringent. This includes borders within the United States of America, where neighboring states might have different drug laws — and even when they have the same laws, bringing cannabis from one state to another violates Federal drug trafficking laws.

This article contains general advice, followed at the reader's own risk. None of it should be taken as legal or medical advice.

Destinations

Laws on possession of small amounts of recreational cannabis, as of 2017.
Blue: Legal or essentially legal
Orange: Illegal but decriminalized
Pink: Illegal but often unenforced
Red: Illegal
Gray: No information

Canada – Medical marijuana has been legal for some time, with restrictions that vary from province to province. Recreational use of marijuana has been legal since October 17, 2018; however, there are restrictions varying by province on how much can be purchased at one time, where cannabis products can legally be purchased, which cannabis products can legally be purchased, and how many cannabis plants can be grown at home. Edibles were legalized one year later on October 17, 2019. Importation and exportation remains illegal. See Cannabis and international travel on the Government of Canada's website for details.
India – While cannabis remains illegal in India, some traditional forms of usage are allowed. One of them is bhang thandai, also known as bhang lassi, an infusion of cannabis paste (buds and leaves) and various nuts, herbs and spices in milk that is available in government authorised shops in parts of the subcontinent, including the states of Rajasthan, Uttar Pradesh, and Bihar.
Netherlands – While it has never been legalized, cannabis and a handful of other substances disallowed elsewhere can be bought in "coffee shops" that are legal. The issue of "drug-tourism", however, is somewhat controversial so there may be some restrictions on foreigners frequenting coffee shops or buying cannabis products there. Cannabis products with no THC content are legal even outside coffee shops.
Spain – While cultivation and possession for private use is legal, selling the drug is a crime.
Thailand – Long infamous for its extremely strict drug laws, Thailand did a drastic U-turn in 2018 when it became the first country in Southeast Asia to legalize medical cannabis (กัญชา ganchaa), expanding this in 2022 to legalize recreational use as well. While extracts of cannabis including all edibles are limited to under 0.2% THC, there are no limits on the potency of plant parts like flowers, leaves or stems. Consumption in public is not permitted, but is now legal in private homes and any spaces like cafes and bars that choose to allow it. Vaping, importing and exporting all remain illegal.
Uruguay – Cannabis products are legal in Uruguay. The law states that buyers have to be over 18 and legal residents of Uruguay, but this is enforced inconsistently at most; less formal vendors like farmers' market stands don't often check IDs.
United States – Several states have legalized use and/or possession of cannabis. While federal law prohibits possession, federal authorities do not pursue intrastate users who abide by state laws. Alaska, Arizona, California, Colorado, Illinois, Maine, Massachusetts, Michigan, Montana, Nevada, New Jersey, New Mexico, New York, Oregon, Vermont, Virginia, Washington State, Washington, D.C. and the U.S. territory of Guam allow cannabis for recreational use and several more have "medical marijuana" laws of varying strictness. Arizona, Montana, New Jersey, and South Dakota voted to allow the recreational use of marijuana on November 3, 2020, and it will be legalized in these states in the future. All jurisdictions that have legalized allow for the commercial distribution of cannabis, except Vermont and Washington, D.C. As the constitution explicitly grants the federal government the right to regulate interstate commerce, carrying cannabis across state lines - even between two states where it is legal - is a federal matter and illegal. Cannabis possession is likewise illegal on some native reservations and all federal enclaves (e.g. airport security, as the TSA is a federal agency), even when surrounded by states where it is otherwise legal. Marijuana-related businesses are routinely denied access to the banking system, even in states where pot is legal (so expect to pay cash) and Customs remains a magical rights-free zone where possession of even a single copy of High Times magazine (protected by the US First Amendment as free speech anywhere else) is grounds enough for an agent to ask if you've ever used marijuana and ban you from the country for a very long time, maybe forever (unless you're a U.S. citizen, in which case you can't be banned from entry, but the magazine is grounds for an extremely intrusive search).

As of 2019, CBD (cannabidiol) products, as long as they contain no more than a very small amount of THC, are at least nominally legal under federal law, as well as in most states. However, because the federal government has yet to issue regulations to fully implement this change, some states continue to ban CBD and hemp products, even prosecuting truckers for transporting hemp that is nominally legal under federal law.

In addition to places where marijuana is legal, there are several places where it is decriminalized, de jure or de facto. This may reach from an internal police memo declaring nonviolent cannabis consumers the "lowest priority" to more or less formal systems whereby cannabis is legal in all but name. The situation may sometimes vary drastically from subnational entity to subnational entity (the de facto limit for "personal consumption" in Berlin is much higher than in Bavaria, for instance, and the police in Bavaria are much more eager to open cases even for personal consumption, even if such cases usually end in acquittal) and in some places even from city to city. Decriminalization might be practiced in various ways; in some cases the authorities confiscate drugs and smoking equipment, without a crime report.

There has been trend towards legalization/decriminalization in the West, but there is still a United Nations agreement that most sovereign states are parties to that classifies marijuana and hashish as controlled substances to be made illegal and combated. Many countries feel still bound by this convention, even if their actual policy is one of de facto decriminalization and laissez-faire. These jurisdictions might still criminalize imports and exports, as well as possession of quantities for more than personal use. The issue of "drug tourism" is a contentious one and most jurisdictions where consumption is legal at least in theory want to discourage people from outside the jurisdiction from visiting just for the consumption of cannabis products.

There are usually DUI laws that apply to cannabis, however legal limits for THC are much less publicized than those for ethanol and some jurisdictions have taken trace amounts of THC in the bloodstream, which - according to current medical consensus - have no impact on driving ability, as grounds for a driving ban and/or fine.

Museums and information

There are several museums dedicated to cannabis history:

Cannabis Museum (Amsterdam).
Hash, Marijuana & Hemp Museum (Amsterdam and Barcelona).
Whakamana Cannabis Museum (Dunedin, New Zealand).
Cannabis Museum (Zagreb, Croatia).
Cannabition (Las Vegas). This has "bongzilla", the world's longest bong at 24 feet (over 7m).

Non-specialist museums may also have cannabis-related exhibits.

Many books are available on cannabis and should be read by the interested individual trying to understand the history and discussions about cannabis:

The Emperor Wears No Clothes. A great book by Jack Herer on the history of cannabis. ISBN 979-8601454001 (updated Aug 2023)
The Medical Cannabis Guidebook. By Jeff Ditchfield and Mel Thomas. Provides explanations on the history of cannabis, the differences between indica and sativa plants and the different strains. ISBN 978-1937866112 (updated Jan 2024)

Stay healthy and safe

Some of the reported adverse health effects of cannabis are still under debate. The safest choice for many people is not to use the drug at all. Smoking any organic substance can release carcinogenic substances as well as harmful carbon monoxide (depending more on the temperature of combustion than the substance itself), so other avenues of consumption are much healthier for the lungs though not risk free either. As for smoking of other substances, there is also a fire risk.

Due to the digestive system, the psychoactive effects from consuming cannabis as food products are delayed relative to smoking. You may think that the dosage was too low because you haven't felt the psychoactive effects yet and decide to consume more, only for the effects from the initial food product to kick in, later followed by the additional effects from the latter food product. Make sure you allow sufficient time after eating cannabis-infused food before consuming more.

Cannabis bought on the black market does not only raise legal concerns; it might include impurities which are much more dangerous than the cannabis itself. Furthermore, there is obviously no legal recourse for bad quality, lower than advertised quantity or any other problem coming from black market dealings.

Cannabis use is also associated with a higher risk of psychosis and schizophrenia, particularly for people with a pre-existing genetic vulnerability. Although there is some scientific discussion about the exact link between cannabis and psychiatric illness, health organizations (including some in countries where cannabis is legalized) typically warn against cannabis use for those with a history of psychosis. They also urge users to take extra care if there are cases of mental illness in their family or if they react unusually strongly (e.g. feel very disoriented or panicked) after using cannabis.

Aside from the physical health effects, intoxication impairs sensory perception and judgment, and might be dangerous and illegal when driving. In many jurisdictions having traces of cannabis (or byproducts) in your urine or bloodstream that are consistent with having consumed it days ago, but - according to all current medical consensus - not linked to any perceptible impairment to driving, will still result in a DUI conviction if caught and might even lead to a (temporary) driving ban.

Medication

See also: Medication

As of 2018, some new prescription medications carefully extract and package just one active ingredient derived from cannabis. For instance, Epidiolex is a purified form of cannabidiol (CBD, one of hundreds of molecules found in marijuana) developed as a treatment for childhood epilepsy.

The legality of these products varies widely internationally; they may be lawfully-regulated prescription medicine in one country, criminalised as illegal street drugs in another, and pending lengthy clinical trials before they can be sold and prescribed somewhere else. Any attempt to carry this medicine into another country is a legal minefield to be avoided at all costs, even if the product is lawful and regulated at its point of origin.

Detection

Cannabis usage can be detected through testing of urine, blood and hair samples. While blood and hair testing requires time and laboratory equipment, urine testing can be done on the spot with cheap and reliable test strips.

Detection times depend on the amount consumed, the consumption frequency, the quality of the material and the metabolism of the person. Compared to other drugs, traces of cannabis can be detected long after the last consumption. It can be difficult to tell how long after the last consumption a test will show a "positive" result, but generally the detection times for the most common test kit (20 ng/mL cut off) are:

Up to 7 days for a one time user
Up to 30 days for a regular weekend user
Up to 80 days for a heavy user

These are examples and should not be used to declare someone "clean" under any circumstances. Cannabis detection times are unpredictable. If in doubt, play it safe.

In some countries, testing positive is all it takes to get you in trouble, even if you used cannabis in a country where it is legal or tolerated. Dubai has a reputation of zero tolerance, with 2 years of imprisonment for peeing positive. In Thailand, consumption without selling or trafficking is a minor offense, but testing positive might nevertheless ruin your trip. In China, testing positive can lead to administration detention up to 15 days with compulsory rehabilitation and deportation. Countries like South Korea and Singapore also have extraterritorial laws to prosecute their own citizens who consume cannabis in foreign countries, even if cannabis is legal in such foreign countries. Singapore takes it a step further by making it a crime for anybody to test positive for cannabis while in Singapore, even if it was consumed overseas, and spot urine tests are sometimes carried out at ports of entry.

In the United Kingdom, driving after consuming cannabis can be extremely legally risky even if you are not impaired, since the legal limits for driving with THC in one's system are exceptionally low, being 2 micrograms per litre of blood; this will easily be exceeded by someone who has recently consumed the drug even if they are not impaired at all, while a habitual consumer may not be "clean" by these standards for weeks. In the event of an accident, there is every chance you could be drug swabbed, and if positive you are likely to be arrested and charged (refusing the swab carries the same penalty as failing it). If you are intent on driving in the UK, the best thing to do is simply not to consume cannabis.

If you choose to take the risk, stay below the radar. Dress decent and avoid that stereotypical stoner look.

Respect

Even in countries where cannabis smoking or intoxication is not a crime, it might be prohibited, or unwelcome, at some premises. At the very least, follow the same restrictions as for tobacco smoking. In a group with other people, think and ask before lighting up.