CBD: What It Is, Effects and Safety | PatientsCann UK

CBD

cannabidiol

pronounced: kan-uh-bih-DY-ol

The calming, non-intoxicating cannabinoid. It will not make you high.

Neutral cannabinoidFormula: C21H30O2Intoxicating: No
Type
Neutral
Formula
C21H30O2
Intoxicating
No
Key focus
Calm & seizures

Cannabidiol · 314.5 g/mol

The molecule

Chemical structure

This is the accurate skeletal structure of CBD, 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.

CalmingAnti-anxietyAnti-seizureAnti-inflammatory

About

What is CBD?

Cannabidiol, or CBD, is the second best-known cannabinoid after THC. Unlike THC, it does not make you high. That single difference is why CBD has been studied so widely, and why low-strength versions are sold in shops as food supplements.

In the plant, CBD starts as its acid form, CBDA, and appears once the plant is heated. Medical CBD is very pure and carefully measured. This is different from many high-street CBD oils, where the real amount can vary a lot.

In the body

How CBD Works

CBD is unusual because it barely fits the CB1 and CB2 receptors directly. Instead it works around the edges of the system. It gently turns down the CB1 receptor, which can soften the high from THC, and it acts on other targets such as serotonin (5-HT1A) receptors and TRPV1 pain channels. It also slows the breakdown of the body's own cannabinoid, anandamide.

The strongest evidence for CBD is in epilepsy. A purified CBD medicine called Epidyolex is licensed in the UK for some rare, severe forms of childhood epilepsy. CBD is also being studied for anxiety, pain and inflammation.

Receptor snapshot

Where CBD Acts

The endocannabinoid system has two main receptors. Here is how strongly CBD acts on each.

CB1Brain & nervous system
Dampens / blocks

Barely fits CB1 by itself. Instead it gently turns the receptor down, which can soften the high from THC.

CB2Immune system & body
Weak / indirect

Very little direct action at CB2.

Beyond CB1 and CB2: Works mostly OUTSIDE the two main receptors: on serotonin (5-HT1A), on TRPV1 heat/pain channels, and by slowing the breakdown of your body’s own cannabinoid, anandamide.

In the plant

How CBD is Made

CBD is made from CBDA, its raw acid form, which the plant builds from the mother cannabinoid CBGA using an enzyme called CBDA synthase.

Heating removes a carbon dioxide group from CBDA and turns it into CBD. Whether a plant makes mostly CBDA or mostly THCA comes down to its genetics.

Comes fromCBDA→ add heat →CBD

Good to know

Safety and Side Effects

CBD is usually well tolerated. Side effects can include tiredness, diarrhoea and changes in appetite. Its most important issue is that it can interact with other medicines, including some epilepsy drugs and blood thinners, by changing how the liver handles them.

Tell your prescriber and pharmacist about any CBD you take, even a shop-bought supplement, so they can check it is safe alongside your other medicines.

Questions

CBD: Common Questions

Does CBD make you high?
No. CBD is non-intoxicating. It does not switch on the CB1 receptor the way THC does, so it will not give you a "high". Many patients say it feels calming rather than mind-altering.
What is CBD used for?
CBD is being studied for anxiety, epilepsy, pain and inflammation. A CBD medicine called Epidyolex is licensed in the UK for some rare, severe forms of epilepsy.
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

  1. 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.
  2. Devinsky, O. et al. (2017) 'Trial of cannabidiol for drug-resistant seizures in the Dravet syndrome', New England Journal of Medicine, 376(21), pp. 2011-2020. doi: 10.1056/NEJMoa1611618.
  3. Izzo, A.A., Borrelli, F., Capasso, R., Di Marzo, V. and Mechoulam, R. (2009) 'Non-psychotropic plant cannabinoids: new therapeutic opportunities from an ancient herb', Trends in Pharmacological Sciences, 30(10), pp. 515-527. doi: 10.1016/j.tips.2009.07.006.
  4. 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).