THC (delta-9-tetrahydrocannabinol) is the compound in cannabis that causes the "high". It binds to CB1 receptors in the brain, which changes mood, perception, memory and coordination. It is one of more than 100 cannabinoids in the plant. CBD, the best-known other one, does not intoxicate. In the UK, THC is a Class B controlled drug.
Key facts
- Full name
- Delta-9-tetrahydrocannabinol (Δ9-THC)
- Discovered
- Isolated and described in 1964 by Yehiel Gaoni and Raphael Mechoulam
- How it works
- Binds strongly to CB1 receptors in the brain and, less strongly, to CB2 receptors
- In the plant
- Made as THCA, which turns into THC when heated
- UK status
- Class B under the Misuse of Drugs Act 1971 (Home Office factsheet, as of October 2026)
- THC vs CBD
- THC intoxicates; pure CBD does not and is not a controlled drug in the UK
Prefer watching? This video covers the key points:
What does THC mean?
THC is short for tetrahydrocannabinol. When people say THC, they usually mean delta-9-THC, the form that occurs naturally in cannabis and causes most of its intoxicating effects. Related compounds such as delta-8-THC and THCV have a similar structure but are separate substances.
THC belongs to a group of compounds called cannabinoids. Cannabis and hemp contain more than 100 of them. THC and CBD (cannabidiol) are the two that have been studied most.
Who discovered THC?
Mechoulam lecturing with the structure of tetrahydrocannabinol behind him, around 1964. Image courtesy of Zach Klein, from his documentary "The Scientist".
The Israeli chemists Yehiel Gaoni and Raphael Mechoulam isolated THC and described its structure in 1964. It was the first time researchers could point to the single compound behind the effects of cannabis. Our article on the history of THC follows the story from there.
How does THC work in the body?
THC acts on the endocannabinoid system, a signalling network made up of cannabinoid receptors, the body's own cannabinoids and the enzymes that break them down. THC binds mainly to CB1 receptors, which are concentrated in brain areas involved in memory, mood, perception and movement. That binding is what causes the high. It also binds to CB2 receptors, which are found mostly in immune tissue (Zou and Kumar, 2018).
Read more in our guide to the endocannabinoid system and in our overview of which cannabinoids are psychoactive.
How does THC form in cannabis?
The plant does not make much THC directly. It makes THCA (tetrahydrocannabinolic acid), which does not intoxicate. Heat removes a carboxyl group and turns THCA into THC, a reaction called decarboxylation. A 2016 laboratory study measured this reaction in cannabis extracts at temperatures between 80 and 145°C (Wang et al., 2016). This is why the Home Office notes that THCA readily breaks down into THC. Our article on how heat affects cannabinoids explains the process.
What is the difference between THC and CBD?
THC and CBD come from the same plant and have the same chemical formula, but they act differently in the body. THC activates the CB1 receptor and intoxicates. CBD does not. In 2018 the World Health Organization's Expert Committee on Drug Dependence concluded that in humans CBD shows no effects indicating any potential for abuse or dependence.
| THC | CBD | |
|---|---|---|
| Causes a high | Yes | No |
| Action at CB1 receptors | Binds and activates them | Low affinity |
| Abuse or dependence potential | Yes, with frequent heavy use | None found by the WHO (2018) |
| UK legal status | Class B controlled drug | Pure CBD is not controlled |
| Picked up by standard drug tests | Yes | No; tests look for THC |
For a fuller comparison, see CBD vs THC and our guide to what CBD is.
What are the side effects of THC?
The effects of THC depend on the amount, the person and how it is used. Research has described these risks:
- Anxiety and paranoia. Some people, especially those prone to anxiety, react with unease or paranoia (Crippa et al., 2009). In a trial where THC was given intravenously, it increased paranoid thinking (Freeman et al., 2015).
- Memory and coordination. THC impairs short-term memory, attention and motor skills, and the effect grows with the dose (Curran et al., 2002; Broyd et al., 2016).
- Psychosis. Heavy use of high-potency cannabis has been linked to a higher risk of psychotic disorders (Johnson-Ferguson and Di Forti, 2021).
- Dependence. In a large US survey, about 8.9% of people who had used cannabis went on to develop dependence (Lopez-Quintero et al., 2011). Regular use also builds tolerance to THC.
Is THC legal in the UK?
No. Cannabis is a Class B drug under the Misuse of Drugs Act 1971, and so are a number of cannabinoids, including THC. Pure CBD, as an isolated substance, is not controlled. The Home Office points out that consumer CBD products can still contain traces of controlled cannabinoids such as THC. Such a product falls outside the controls only if it meets the "exempt product" conditions in the Misuse of Drugs Regulations 2001, one of which is that no controlled drug exceeds 1 mg per container. Our guide Is CBD oil legal in the UK? explains the rules in more detail.
THC-based medicines are a separate category. In the UK they are only available on prescription. Our guide to THC oil explains how it differs from CBD oil.
How long does THC stay in your system?
It depends on how often and how much someone uses, and on the test. In a study of 86 chronic users kept under supervised abstinence, urine tests stayed positive for a mean of 27 days, and some people took up to 77 days to test consistently negative (Ellis et al., 1985). Occasional use clears much faster. Our guide to CBD, drug tests and driving explains what this means for people who use CBD products.
From our production
The question I am asked most is how much THC is in our products. We test every batch in Switzerland and print the THC content on the certificate of analysis to two decimal places. We have never had a failed test since 2013.
— Robin Roy Krigslund-Hansen, co-founder and CEO
Frequently asked questions
What is THC?
THC (tetrahydrocannabinol) is the main intoxicating compound in cannabis. It binds to CB1 receptors in the brain and causes the high. It is one of more than 100 cannabinoids in the plant.
What does THC stand for?
THC stands for tetrahydrocannabinol. The form found naturally in cannabis is delta-9-tetrahydrocannabinol, often written Δ9-THC.
What is the difference between THC and CBD?
Both come from cannabis and share the same chemical formula. THC activates CB1 receptors and intoxicates; CBD does not. In the UK, THC is a Class B drug, while pure CBD is not controlled.
Is THC addictive?
It can be. Frequent, heavy use can lead to dependence and withdrawal symptoms. In a large US survey, about 8.9% of people who had used cannabis developed dependence.
Can you overdose on THC?
A fatal overdose from cannabis alone is unlikely, but too much THC can cause severe anxiety, panic, paranoia, a racing heart, confusion and vomiting. Anyone with these symptoms should seek medical help.
Can THC show up on a drug test?
Yes. Urine, blood, saliva and hair tests look for THC or its breakdown products. After heavy, long-term use, urine tests can stay positive for weeks.
Related guides
This article is for information only and does not describe any product in our shop. Formula Swiss CBD oils are cosmetic products for use on the skin. They are not medicines. See our full disclaimer.
Last reviewed:
Sources
- Gaoni Y, Mechoulam R. Isolation, structure, and partial synthesis of an active constituent of hashish. J Am Chem Soc 1964;86(8):1646–1647.
- Zou S, Kumar U. Cannabinoid receptors and the endocannabinoid system: signaling and function in the central nervous system. Int J Mol Sci 2018. doi:10.3390/ijms19030833
- Wang M, Wang YH, Avula B, et al. Decarboxylation study of acidic cannabinoids. Cannabis Cannabinoid Res 2016. doi:10.1089/can.2016.0020
- World Health Organization, Expert Committee on Drug Dependence. Cannabidiol (CBD): critical review report. Geneva: WHO; 2018.
- Crippa JA, Zuardi AW, Martín-Santos R, et al. Cannabis and anxiety: a critical review of the evidence. Hum Psychopharmacol 2009. doi:10.1002/hup.1048
- Freeman D, Dunn G, Murray RM, et al. How cannabis causes paranoia: using the intravenous administration of Δ9-THC to identify key cognitive mechanisms leading to paranoia. Schizophr Bull 2015. doi:10.1093/schbul/sbu098
- Curran HV, Brignell C, Fletcher S, et al. Cognitive and subjective dose-response effects of acute oral Δ9-THC in infrequent cannabis users. Psychopharmacology (Berl) 2002. doi:10.1007/s00213-002-1169-0
- Broyd SJ, van Hell HH, Beale C, et al. Acute and chronic effects of cannabinoids on human cognition: a systematic review. Biol Psychiatry 2016. doi:10.1016/j.biopsych.2015.12.002
- Johnson-Ferguson L, Di Forti M. From heavy cannabis use to psychosis: is it time to take action? Ir J Psychol Med 2021.
- Lopez-Quintero C, Pérez de los Cobos J, Hasin DS, et al. Probability and predictors of transition from first use to dependence on nicotine, alcohol, cannabis, and cocaine. Drug Alcohol Depend 2011. doi:10.1016/j.drugalcdep.2010.11.004
- Ellis GM, Mann MA, Judson BA, et al. Excretion patterns of cannabinoid metabolites after last use in a group of chronic users. Clin Pharmacol Ther 1985. doi:10.1038/clpt.1985.226
- Home Office. Drug licensing factsheet: cannabis, CBD and other cannabinoids. Updated 3 October 2024.
