Delta-9-THC: What It Is, Effects and Safety | PatientsCann UK Skip to main content Back to Cannabinoids Guide THC Delta-9-THC delta-9-THC, dronabinol pronounced: DEL-tuh nine tet-ruh-hy-droh-kuh-NAB-ih-nol The main active cannabinoid – the one that makes you feel “high”. Neutral cannabinoidFormula: C21H30O2Intoxicating: Yes TypeNeutral FormulaC21H30O2 IntoxicatingYes Key focusPain & nausea Delta-9-tetrahydrocannabinol · 314.5 g/mol The molecule Chemical structure This is the accurate skeletal structure of Delta-9-THC, drawn from PubChem data. Each corner and line-end is a carbon atom, and the red O marks oxygen. Its formula is C21H30O2 and it weighs 314.5 g/mol. Pain reliefAppetiteAnti-sicknessEuphoria About What is Delta-9-THC? Delta-9-THC is the most famous cannabinoid, and the one that makes cannabis feel intoxicating. It was first identified by scientists Raphael Mechoulam and Yechiel Gaoni in 1964. When people talk about how “strong” a cannabis product is, they usually mean how much THC it contains. The fresh plant does not actually hold much THC. It makes an acid called THCA instead. THC only appears once the plant is dried, then heated, vaped or smoked. This is why the THC number on a lab report tells you how much becomes available after heating. In the body How THC Works THC works by fitting into the CB1 receptor, which sits mostly in the brain and nervous system. Switching CB1 on changes how nerve cells pass messages. This is what causes the “high”, and it is also how THC eases pain, calms nausea and brings on hunger. THC acts on CB2 receptors too, which are linked to the immune system. UK specialists may consider a THC-containing medicine for problems such as long-term pain, muscle spasms in multiple sclerosis, and sickness from chemotherapy, when licensed treatments have not helped. The right amount is very personal, so prescribers usually start low and go slow. Receptor snapshot Where THC Acts The endocannabinoid system has two main receptors. Here is how strongly Delta-9-THC acts on each. CB1Brain & nervous systemStrong Switches on CB1 in the brain and nerves. This is what causes the “high”, and also eases pain, nausea and appetite loss. CB2Immune system & bodyPartial Also activates CB2 on immune cells, which is linked to inflammation. In the plant How THC is Made THC begins life as THCA, its raw acid form, which the plant builds from the “mother” cannabinoid CBGA. THCA on its own is not intoxicating. Heat removes a small piece of the THCA molecule (a carbon dioxide group) and turns it into THC. This step is called decarboxylation. Later, as cannabis ages and meets air and light, THC slowly changes again into CBN. Comes fromTHCA→ add heat →Delta-9-THC Good to know Safety and Side Effects THC can cause a fast heartbeat, dry mouth, red eyes, dizziness, and feelings of anxiety or paranoia, especially at higher doses or in people who are new to it. It affects your ability to drive and use machinery. It is not recommended in pregnancy, and heavy long-term use can lead to dependence in some people. If you ever take too much and feel unwell, find a calm space, sip water, and wait it out; the feeling passes. Always follow your prescriber’s dose and never mix your medicine with alcohol or other drugs without advice. Questions Delta-9-THC: Common Questions Will THC get me high? Yes. Delta-9-THC is the cannabinoid responsible for the “high” feeling. This happens because it switches on CB1 receptors in the brain. The amount you feel depends on the dose, the product and your own tolerance. Is THC legal in the UK? THC is a controlled drug, but since November 2018 specialist doctors can legally prescribe cannabis medicines that contain THC. You cannot buy high-THC products legally without a prescription. PreviousCBGA NextCBD Back to full Cannabinoids Guide Important: This page is for education only. It is not medical advice. Cannabinoid research is still developing, and many studies have been done in cells or animals rather than people. Always speak to your prescriber before changing your treatment. PatientsCann UK does not recommend any specific cannabis product. References Gaoni, Y. and Mechoulam, R. (1964) ‘Isolation, structure, and partial synthesis of an active constituent of hashish’, Journal of the American Chemical Society, 86(8), pp. 1646-1647. doi: 10.1021/ja01062a046. Pertwee, R.G. (2008) ‘The diverse CB1 and CB2 receptor pharmacology of three plant cannabinoids: delta-9-tetrahydrocannabinol, cannabidiol and delta-9-tetrahydrocannabivarin’, British Journal of Pharmacology, 153(2), pp. 199-215. doi: 10.1038/sj.bjp.0707442. Russo, E.B. (2011) ‘Taming THC: potential cannabis synergy and phytocannabinoid-terpenoid entourage effects’, British Journal of Pharmacology, 163(7), pp. 1344-1364. doi: 10.1111/j.1476-5381.2011.01238.x. National Center for Biotechnology Information (2025) PubChem Compound Database. Bethesda: U.S. National Library of Medicine. Available at: https://pubchem.ncbi.nlm.nih.gov (Accessed: 29 July 2026).
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