UK cannabis law, in plain English.
Cannabis is a Class B controlled substance in the UK under the Misuse of Drugs Act 1971. That's the legal reality, stated plainly. Here's what it actually means in practice, without the scaremongering. If you're outside the UK, check your local laws.
This page explains the law as it stands. It isn't legal advice. If you're facing a specific situation, speak to a solicitor or a drugs-law charity like Release (see the note at the end).
If what you really want to know is what happens in the moment, what the police can and can't do if they stop you, and what you do and don't have to say, that's a page of its own: Know Your Rights.
Possession
The maximum penalty for possessing a Class B drug is up to 5 years in prison, an unlimited fine, or both (GOV.UK). That's the ceiling, not the norm. In practice, for a small amount for personal use with no aggravating factors, the police often use lower-level responses: a cannabis warning, or an on-the-spot penalty notice for disorder (a fine of around £90), with escalation for repeat encounters. There's real police discretion here, and outcomes vary by force and circumstances, but a caution or conviction still creates a record that can show up in enhanced checks and affect travel to some countries.
Supply and production
Supply and production are treated far more seriously: up to 14 years in prison, an unlimited fine, or both (GOV.UK). The important thing many people don't realise is how broadly "supply" is defined. It doesn't require selling. Passing a joint to friends, or buying a batch and splitting the cost, can in principle count as supply ("social supply"). Growing your own plants is production, regardless of whether any of it is sold. Quantity, cash, scales, bags and messages are the kinds of things used to argue intent to supply.
Drug-driving
This is where people most often come unstuck without realising the risk, and it's worth understanding properly, because the way the law works catches people who genuinely thought they were fine to drive.
There are really two ways you can be caught. The older offence is driving while impaired by drugs. But since March 2015, England and Wales also have a "per se" limit: it's a separate offence simply to drive with more than 2 micrograms of THC per litre of blood, whether or not your driving is actually affected (GOV.UK; the figure is set in the Drug Driving (Specified Limits) Regulations 2014). Scotland brought in the same limits in 2019. That 2µg/L threshold is deliberately low, low enough that "I don't feel high" is no defence at all.
And this is the part that catches regular users out: THC lingers in the body far longer than the high does, so a frequent user can still be over the limit many hours, sometimes into the next day, after they last felt anything. MIXEDEvidence strength How long THC stays in blood above the 2µg/L limit varies a lot between people, depending on how often and how heavily they use, their body composition and metabolism. Occasional users typically drop below the limit within a few hours; frequent, heavy users can retain detectable blood THC much longer. Key study: Karschner et al. (2009), in Addiction, found measurable THC in the blood of chronic daily users for days after their last use, showing that blood THC is a poor marker of "recent" use in regular users. Why it's "mixed": the general pattern is well established, but there's no reliable way to translate "I stopped X hours ago" into "I'm now under the limit". The safe reading is simply: if you use regularly, don't assume a night's sleep clears you.
How it's enforced. At the roadside, police can carry out a Field Impairment Assessment (a set of coordination tasks) and use a saliva swab that screens for cannabis and cocaine in a few minutes. A positive swab, or reasonable suspicion of impairment, leads to arrest and an evidential blood test at the station, which is what actually decides the case. Refusing to give a blood sample without a good reason is itself an offence, and carries penalties in the same bracket as failing the test.
The penalties. A conviction carries a minimum 1-year driving ban, an unlimited fine, up to 6 months in prison and a criminal record, and the endorsement stays on your licence for 11 years (GOV.UK). At the extreme, causing death by careless driving under the influence of drugs carries a maximum of life imprisonment. Beyond the court, the knock-on effects are real: insurance premiums that can multiply, jobs that require driving or a clean record, and problems entering some countries. Practically: don't drive after using. Harm Reduction covers this too.
One exception matters here. A statutory medical defence can apply if you're driving on lawfully prescribed cannabis and following the prescribing advice, provided you're not impaired. It's narrower and more fraught than it sounds. The Medical cannabis page covers it in full.
Medical cannabis
Since 1 November 2018, cannabis-based products for medicinal use (CBPMs) have been legal in the UK on prescription, but the route is narrow and often misunderstood. They can only be prescribed by a specialist doctor, never a GP. NHS prescriptions are very rare, so in practice most patients go through a private clinic. This is factual, not a nudge. This site is not a "get a prescription" service. We've given it a page of its own: Medical cannabis in the UK covers who can prescribe, the licensed medicines, the NHS-vs-private reality, and what living with a prescription means for driving and work.
Not in the UK?
Everything above is UK law. Cannabis law varies enormously between countries, from full legalisation to severe criminal penalties. If you're elsewhere, see where cannabis is legal around the world for a country-by-country snapshot, and always check the current law where you actually are.
This isn't legal advice
This page is general information, not advice on your situation. For that, contact a criminal-defence solicitor, Citizens Advice, or Release, the UK's centre of expertise on drugs and drugs law, which runs a free, confidential helpline. For non-judgemental information about cannabis itself, there's always FRANK.