CBD and THC are different cannabinoids. In a prescription context, their differences shape the evidence, potential effects and risks, regulatory context, and the questions a prescriber has to consider.
The practical difference is that CBD does not produce the high associated with THC, while THC is the cannabinoid most associated with intoxication and impairment. Neither name, on its own, tells you whether a product is suitable, what outcome it will have or whether it can be used safely alongside other medicines.
CBD evidence is formulation-specific
CBD means cannabidiol. Its strongest clinical evidence is specific to defined medicines and indications. Randomised trials of purified CBD as an add-on treatment studied particular severe epilepsies, including Dravet and Lennox–Gastaut syndromes. Those trials used a defined formulation, specialist oversight and selected patient groups. They are not evidence that every CBD oil, cannabis flower or product containing CBD treats epilepsy, pain, sleep problems or anxiety.
CBD can also matter for medicine interactions. A dose-ranging clinical-pharmacology study in children with Dravet syndrome recorded interactions involving clobazam’s active metabolite and liver-transaminase elevations in some participants also taking valproate. That finding is a reason to disclose medicines to the clinical team, not a basis for self-managing a prescription. Read the CBD evidence page.
THC, intoxication and safety context
THC usually means delta-9-tetrahydrocannabinol. In a controlled laboratory challenge in healthy people, intravenous THC produced transient changes in perception, anxiety, mood and cognition. That experiment was not a study of a UK prescribed product or an individual treatment outcome, but it helps explain why THC requires careful clinical and safety context.
The NHS distinguishes THC from CBD and notes risks associated with THC-containing cannabis products. THC and cannabinol derivatives also sit within the UK controlled-drug framework. A THC figure is a composition measurement; it is not a measure of benefit, suitability or legal or driving clearance. Read the THC evidence page.
CBD and THC in a controlled oral study
It is tempting to assume that more CBD always softens THC effects. A randomised double-blind crossover clinical-pharmacology study tested oral extracts in 18 healthy adults, each with the same THC amount but one with much more CBD. Under those experimental conditions, the CBD-containing extract produced higher measured THC exposure and more reported anxiety, sedation, memory difficulty and cognitive or psychomotor impairment.
The result is limited to specific oral preparations and healthy adults. It still shows why a CBD:THC label cannot promise that a product will be milder or safer. THC:CBD ratios explained sets out the study limits in more detail.
Prescription medicines, consumer CBD and labels
A prescribed cannabis-based medicinal product and a consumer product marketed as CBD are not interchangeable categories. The MHRA states that products making medicinal claims must meet the applicable medicines requirements unless exempt. The Home Office also distinguishes pure isolated CBD from preparations that may raise different controlled-cannabinoid questions. A CBD label alone is not proof of quality, efficacy, medical authorisation or suitability.
The cannabinoid reference and MCPH glossary explain the names, evidence types and regulatory terms that appear in these discussions.
Sources
- Trial of Cannabidiol for Drug-Resistant Seizures in the Dravet Syndrome (PMID 28538134); double-blind placebo-controlled randomised trial of purified CBD as add-on treatment in a defined epilepsy population; it does not establish effects outside that formulation and population.
- Cannabidiol in patients with seizures associated with Lennox-Gastaut syndrome (PMID 29395273); randomised double-blind trial of purified CBD as add-on treatment; not evidence for general CBD products.
- The psychotomimetic effects of intravenous delta-9-tetrahydrocannabinol in healthy individuals (PMID 15173844); controlled human laboratory challenge, not a prescribed-product trial.
- Oral THC when coadministered with CBD (PMID 36780161; DOI); randomised double-blind crossover study in 18 healthy adults using specified oral extracts; not a universal ratio rule.
- MHRA statement on products containing CBD ; UK regulatory statement; a CBD product making medical claims is not automatically an authorised medicine.
