Last updated: October 2026
CBD and THC are both cannabinoids from the cannabis plant, but THC makes you high and CBD doesn’t. In the UK, THC is a controlled Class B drug, while CBD is legal in food supplements that meet the rules. THC also impairs driving and shows up on drug tests.
Below: a side-by-side comparison, why two molecules with the same formula act so differently, effects and side effects, the UK’s 1mg THC rule, drug tests, the driving limit, other cannabinoids such as THCA and CBN, and how to avoid THC.
CBD vs THC at a glance
| CBD (cannabidiol) | THC (tetrahydrocannabinol) | |
|---|---|---|
| Gets you high? | No | Yes |
| UK legal status | Legal in compliant food supplements | Controlled, Class B |
| Addictive? | No evidence of abuse potential | Can cause dependence |
| Driving | Didn’t impair driving in a 2020 trial; avoid if drowsy | Impairs driving; illegal above a very low blood limit |
| Drug tests | Not usually tested for | The main thing tests look for |
| Main source | Hemp | Drug-type cannabis |
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View productSame formula, different shape
CBD (cannabidiol) and THC (delta-9-tetrahydrocannabinol) are built from exactly the same atoms: 21 carbon, 30 hydrogen and 2 oxygen, written C21H30O2. The difference is how those atoms are arranged. In THC, part of the molecule closes into an extra ring; in CBD that ring stays open.
That small change alters how each one fits the body’s cannabinoid receptors, which is why one is intoxicating and the other isn’t. In the living plant, THC starts out mostly as an acid, THCA, which breaks down into THC over time and with heat. For how hemp seed oil differs from both, see hemp oil vs CBD oil.
How they affect you
THC strongly activates CB1 receptors in the brain, which causes the high, changes in perception, appetite and memory, and sometimes anxiety or paranoia. FRANK warns that regular cannabis use can lead to dependence and, in some people, mental health problems. CBD binds only weakly to CB1 and acts on several other targets, so it doesn’t change your state of mind. In trials, even large doses of CBD felt like a placebo. See does CBD get you high?, what CBD feels like and the endocannabinoid system.
In pharmacology terms, THC is a partial agonist at the CB1 and CB2 receptors: it switches them on, though not fully. In lab studies CBD behaves quite differently, and can block other compounds from switching those receptors on rather than activating them itself. For what the research does and doesn’t show for CBD on its own, see CBD and anxiety and CBD for pain.
Side effects compared
THC’s side effects come mostly from the high itself. CBD’s are usually milder and more physical, and in trials they were mostly seen at doses far above supplement levels.
| Side effect | CBD | THC |
|---|---|---|
| Feeling high | No | Yes |
| Anxiety or paranoia | Not a typical effect | Can happen, especially with a lot |
| Physical effects | Tiredness, diarrhoea, appetite changes | Hunger, drowsiness, feeling sick |
| Dependence | No abuse signal in a 2017 study | Cravings and withdrawal in heavy users |
iCBD can also interact with some medicines, so check with your GP or pharmacist first if you take any. See CBD side effects for what’s normal and who should avoid CBD, and our CBD dosage guide for how much to take.
CBD vs THC for sleep
Neither is an approved sleep aid in the UK. THC can make people drowsy in the short term, but it changes the shape of your sleep, wears off with regular use and often disturbs sleep when you stop. CBD on its own hasn’t shown a clear effect on sleep in controlled trials. Here’s what the research actually says.
THC and sleep
Many people find THC sedating. Older sleep-lab studies found that a dose of cannabis or THC shortened the time it took to fall asleep and reduced REM sleep, the stage in which most dreaming happens. The catch is what happens next. Repeated use builds tolerance, including to THC’s effects on sleep, and a 2017 review concluded that THC could impair sleep quality over the long term.
Stopping after regular, heavy use is often hard on sleep. A systematic review of cannabis withdrawal studies found sleep was frequently interrupted, and sleep-lab studies of heavy users have recorded less total sleep and less REM sleep during abstinence.
CBD and sleep
The evidence for CBD alone is small and mixed. In a 2018 placebo-controlled sleep-lab trial, a single 300mg dose of CBD made no measurable difference to the sleep of healthy volunteers. A 2025 meta-analysis of six randomised trials found that CBD-only products had no significant effect on self-rated sleep quality, while products containing THC or other cannabinoids scored better. A 2020 systematic review found there wasn’t enough evidence to support routine use of any cannabinoid for any sleep disorder.
Trial doses are also far higher than the FSA’s precautionary advice of 10mg a day: 300mg is 30 times that figure. CBD supplements have no authorised health claims, and CBD isn’t a treatment for insomnia or any other sleep problem.
| THC | CBD on its own | |
|---|---|---|
| Short-term effect in studies | Often drowsy; may fall asleep faster | No clear effect on sleep in a 300mg sleep-lab trial |
| Sleep stages | Less REM (dreaming) sleep | No change to normal sleep stages in that trial |
| With regular use | Tolerance builds; sleep quality may suffer | Few long-term studies |
| Stopping | Sleep often disrupted during withdrawal | No sign of abuse potential in a 2017 study |
| UK legal status | Class B drug; not prescribed for insomnia | Legal in compliant food supplements; not a sleep treatment |
What UK law allows
THC is a Class B drug, so there is no legal way to buy it for sleep. On the NHS, cannabis-based medicines can only be prescribed by a specialist hospital doctor, for a small number of conditions: rare, severe forms of epilepsy, sickness caused by chemotherapy and muscle stiffness in multiple sclerosis. Insomnia isn’t one of them. The NHS also warns that cannabis products sold online without a prescription are likely to be illegal and have a good chance of containing THC.
CBN (cannabinol), often marketed abroad as a sleep cannabinoid, is a Class B drug too, according to the Home Office. Gummies, vapes and oils made to contain THC or CBN are controlled in the UK, whatever the label says.
If poor sleep is affecting your days, your GP is the place to start, and our guide to insomnia covers what the NHS recommends. For a closer look at the studies, read what the research says about CBD and sleep. If you’d like CBD as part of your evening routine, our guide to the best CBD oil for sleep explains how to choose one.
UK law
Cannabis and THC are Class B drugs. CBD itself isn’t controlled, but CBD products must contain no more than tiny traces of THC, and CBD food products must be linked to an application on the FSA’s public list. Hemp can be grown only under a Home Office licence. See is CBD legal in the UK? and hemp vs marijuana.
The 1mg THC rule
Pure CBD on its own isn’t a controlled drug, the Home Office confirms. But CBD is hard to separate completely from other cannabinoids, so most CBD products contain at least traces of controlled ones such as THC and CBN. They can only be sold legally if they meet all three conditions of the “exempt product” rule in regulation 2 of the Misuse of Drugs Regulations 2001:
- the product isn’t designed to give the controlled drug to a person or animal;
- the controlled drug is packaged so it can’t easily be recovered;
- no one component part of the product contains more than 1mg of the controlled drug.
The 1mg limit applies to the whole container, such as a bottle of oil, not to a single dose. The Home Office expects businesses to prove it with testing at a lab accredited to ISO 17025.
CBD as food: the FSA rules
CBD extracts are novel foods, so they need authorisation before they can be sold as food. In England and Wales, only products linked to applications on the FSA’s public list can stay on sale while that process runs. The FSA advises healthy adults to have no more than 10mg of CBD a day, and has set a safe upper limit of 70 micrograms of THC a day from food. It doesn’t recommend CBD for under-18s, anyone pregnant, breastfeeding or trying to conceive, or people taking medication, unless under medical direction. For the latest decisions, see the FSA’s first CBD approvals explained.
Penalties for THC
Cannabis is a Class B drug. The maximum penalty for possession is five years in prison, an unlimited fine or both; for supply or production it is 14 years. THC is legal only in prescribed medicines, and NHS prescriptions are limited to a few conditions: see medical cannabis in the UK.
Labels aren’t always right. An independent analysis of 29 CBD oils on sale in the UK, published in 2020, found that 55% contained measurable THC or CBN, both controlled, and only 38% were within 10% of the CBD content on the label. That is why the batch lab report matters.
Drug tests and driving
- Drug tests look for THC and its breakdown products, not CBD. A CBD product containing traces of THC could still cause a positive result. See CBD and drug tests.
- Driving: it’s illegal to drive with certain levels of illegal drugs, including cannabis, in your blood, even if your driving seems fine. Police can use roadside kits that screen for cannabis. A 2020 on-road trial found CBD-dominant cannabis didn’t impair driving, while THC did. Don’t drive if any product makes you drowsy. See CBD and driving.
How much THC does it take to fail a test?
Less than you might think. In a 2026 US trial, 60 adults took 100mg of CBD in MCT oil containing between 0 and 3.7mg of THC. After a single dose, at least one person in every group taking 1mg of THC or more failed a urine test. Over two weeks of twice-daily use, there were positive tests in every group whose oil contained any THC, even 0.5mg, and one sample in the CBD-only group also tested positive. An earlier study found that single 100mg doses of pure CBD didn’t produce a confirmed positive result.
Standard tests can’t tell whether THC came from a legal hemp product or from cannabis. If you are tested at work or in sport, a broad spectrum or isolate product with a batch report showing THC as not detected is the safer choice.
The THC driving limit
In England and Wales, the legal limit for driving is 2 micrograms of THC per litre of blood, and Scotland uses the same figure. There is no limit for CBD. A drug-driving conviction means a minimum one-year driving ban, an unlimited fine, up to 6 months in prison and a criminal record. FRANK warns that driving when high can double your chances of a serious or fatal crash.
Medicines that use CBD and THC
| Medicine | Contains | Licensed in the UK for |
|---|---|---|
| Epidyolex | Purified CBD | Seizures in some rare forms of epilepsy |
| Sativex | THC and CBD spray | Muscle spasticity in multiple sclerosis |
| Nabilone | A synthetic THC-like drug | Nausea from chemotherapy |
These are prescription medicines at much higher doses than supplements. See medical cannabis UK and prescription CBD.
Other cannabinoids: THCA, CBN, CBG, delta-8 and THCV
CBD and THC are only two of many cannabinoids in cannabis. Here is how some others you may see sold online compare in UK law.
| Cannabinoid | What it is | UK status |
|---|---|---|
| THCA | The raw acid form of THC | Pure THCA isn’t controlled, but it breaks down into THC (Class B) |
| CBN | Forms as THC ages | Class B |
| Delta-8 THC | A close relative of THC | Controlled: counts towards the 1mg rule |
| THCV | A THC relative found in some strains | Controlled: counts towards the 1mg rule |
| CBG | Cannabigerol, sold much like CBD | Not named in the Home Office factsheet; products must still meet the THC rules |
Products sold as THCA flower, CBN gummies or delta-8 vapes carry real legal risk in the UK, whatever the label says. Read more in CBD vs CBN, what is THCV?, CBG vs CBD and delta-8 THC in the UK.
How to avoid THC
- Choose broad spectrum or isolate, not full spectrum. See full vs broad spectrum.
- Check the batch lab report shows THC as not detected. See how to read a lab report.
- Buy from FSA-listed UK products, not unregulated imports.
Full spectrum vs broad spectrum vs isolate
| Type | THC | What else is in it |
|---|---|---|
| Full spectrum | Small amounts | Other cannabinoids and terpenes |
| Broad spectrum | Removed to non-detectable levels | Other cannabinoids and terpenes |
| Isolate | None | CBD only |
More detail in CBD distillate vs isolate vs full spectrum.
CBD vs THC gummies, vapes and drinks
The difference is the same whatever the format. A legal CBD gummy, vape or drink in the UK contains CBD with no more than tiny traces of THC. Products sold as THC gummies, THC vapes or THC drinks are controlled drugs here, and the NHS warns that cannabis products bought online without a prescription have a good chance of containing THC. CBD food and drink must also be linked to the FSA public list.
Our CBD oils and capsules are broad spectrum with 0% THC, tested at ISO 17025 accredited labs (reports on request via our lab testing page) and on the FSA public list. Our Broad Spectrum CBD Oil is simply CBD in organic MCT oil. For help choosing, see best CBD oil UK. All our products are for adults (18+) only. The FSA’s 10mg a day figure is precautionary advice rather than a legal limit, set while longer-term safety research continues. At Evopure we think it is a very cautious figure, and many adults use more. If you go above it, increase slowly, and check with your GP or pharmacist first if you take any medication. We don’t recommend our products during pregnancy or breastfeeding.
For the full picture, see what is CBD? The complete UK guide.
Video: the difference between CBD and THC
A short explainer on how CBD and THC differ and what that means for you.
Noticed a racing heart after a CBD product? Read why CBD can cause palpitations (and why THC is often the real culprit).
See also how THC is removed during CBD extraction.
See also CBD vs Sativex for MS for how the THC and CBD spray compares with CBD supplements.
Related guides
- What is full spectrum CBD?, the type of CBD oil that keeps a small amount of THC.
- CBD isolate, the THC-free form of CBD.
- CBD tolerance vs THC tolerance.
- CBD for athletes: WADA rules and the THC limit.
- Is delta 8 legal in the UK?
- For the research on CBD on its own, area by area, see CBD benefits and side effects: the evidence.
- THC rules differ hugely abroad. Our guide to travelling with CBD oil lists the rules country by country, with official sources.
- Both cannabinoids can affect how some medicines are processed; for CBD, see which drugs interact with CBD.
- CBN is what THC turns into as it ages, and it is also a Class B drug in the UK: see CBD vs CBN.
- The CBD and THC difference is also why many scholars view them differently, as our guide is CBD oil halal? explains.
- The two also leave the body on different timelines: see how long CBD stays in your system compared with THC detection windows.
- Wondering about cannabis rubs? See is there a Tiger Balm with CBD or THC.
- Some argue CBD works better with a little THC; our guide to the CBD entourage effect looks at the evidence.
- THC can be toxic to animals, so keep cannabis products away from pets: see what to give a dog for fireworks, and what not to.
- Choosing a THC-free product? Our CBD capsules UK guide explains why full spectrum carries more legal and drug test risk.
- Strength on a CBD label describes the CBD, not the THC; our guide to CBD strength explains how to read mg and %.
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