Key Differences at a Glance
This table provides a simplified comparison for general understanding. Individual responses to cannabinoid medicines vary. Always discuss your specific situation with your specialist doctor.
| Property | CBD | THC |
|---|---|---|
| Full chemical name | Cannabidiol | Delta-9-tetrahydrocannabinol |
| Psychoactive? | No — does not produce a 'high'This is the most important practical difference for patients. | Yes — produces euphoria and altered perception |
| Legal status (UK) | Legal if derived from approved hemp (< 0.2% THC) or prescribed as a medicine | Controlled substance (Schedule 2). Legal only when prescribed by a specialist doctor. |
| How it works (simplified) | Modulates multiple receptor systems (serotonin, TRPV1, GPR55) without directly activating CB1 receptors | Directly activates CB1 receptors in the brain and CB2 receptors in the immune system |
| Main therapeutic areas | Epilepsy, anxiety, inflammation, neuroprotection | Spasticity, nausea/vomiting, pain, appetite stimulation |
| UK-licensed medicines | Epidyolex (pure CBD oral solution) | Sativex (CBD:THC 1:1 spray), Nabilone (synthetic THC analogue) |
| Common side effects | Drowsiness, diarrhoea, reduced appetite, liver enzyme changes | Dizziness, dry mouth, euphoria/dysphoria, impaired concentration, increased heart rate |
| Risk of dependence | No evidence of dependence or abuse potential (WHO 2017) | Low to moderate risk with prolonged use; withdrawal symptoms possible |
| Drug interactions | Inhibits CYP3A4 and CYP2C19 — may increase levels of other medicinesBoth require careful review of existing medications by a specialist. | Metabolised by CYP3A4 — levels affected by other medicines |
| Driving | No impairment expected at therapeutic doses | May impair driving ability. Legal limits apply (UK drug-driving law). |
| Monitoring required | Liver function tests (LFTs) recommended, especially with valproate | Psychiatric monitoring; cardiovascular caution in at-risk patients |
How They Work in the Body
CBD (Cannabidiol)
- Does not directly activate the brain's CB1 receptors (no 'high')
- Works on multiple targets: serotonin receptors (mood), TRPV1 (pain), GPR55 (inflammation)
- May reduce inflammation, calm overactive nerve signals, and modulate immune responses
- Processed by the liver (CYP enzymes) — can interact with other medicines
THC (Tetrahydrocannabinol)
- Directly activates CB1 receptors in the brain (produces psychoactive effects)
- Also activates CB2 receptors in the immune system (may reduce inflammation)
- Can reduce muscle spasticity, nausea, and pain signals
- Also processed by the liver (CYP3A4) — levels can be affected by other medicines
Important Safety Information
Tell your doctor about all medicines
Both CBD and THC can interact with other medications. Always provide a complete list of everything you take, including supplements.
Pregnancy and breastfeeding
Cannabinoid medicines are not recommended during pregnancy or breastfeeding. Discuss family planning with your specialist.
Mental health
THC may worsen anxiety, psychosis, or depression in some people. CBD is generally better tolerated psychiatrically, but monitoring is still important.
Young people (under 25)
The developing brain may be more sensitive to THC. Extra caution and monitoring apply for younger patients.
Liver health
CBD can affect liver enzymes. Regular blood tests may be needed, especially if you take other medicines processed by the liver.
Driving and machinery
THC can impair your ability to drive. UK drug-driving laws apply even to prescribed THC medicines. CBD at therapeutic doses is not expected to impair driving.
How Cannabinoid Medicines Are Accessed in the UK
NHS or Private Prescription
Epidyolex, Sativex, and Nabilone are licensed medicines with full regulatory approval for specific conditions.
- ✓Prescribed by specialists
- ✓Full clinical trial evidence
- ✓Available on NHS for approved indications
Specialist Clinic Prescription
Cannabis-based products for medicinal use (CBPMs) prescribed when licensed options have been tried or are unsuitable.
- ✓Specialist doctor only
- ✓Individual patient basis
- ✓Usually private prescription
Over-the-Counter CBD Products
CBD oils, capsules, and topicals sold as food supplements. Not regulated as medicines and not covered on this site.
- ✗No medical claims permitted
- ✗Variable quality and dosing
- ✗Not a substitute for prescribed medicine
Frequently Asked Questions
Important Notice
This page provides general educational information about CBD and THC as classes of cannabinoid. It does not recommend any specific product or treatment. Cannabinoid medicines should only be used under the supervision of a qualified specialist doctor.
If you are considering cannabinoid medicine, speak to your GP about a referral to a specialist, or contact a specialist cannabis clinic directly. Do not stop or change any existing medication without medical advice.