THC vs CBD: the differences, and the THC allowed in CBD

Hemp (Cannabis sativa L.) makes its cannabinoids from one shared precursor, CBGA. The enzyme a variety carries decides whether that precursor becomes mostly THCA or mostly CBDA, the acidic forms present in the fresh plant. Heat then removes a carboxyl group. That step, decarboxylation, gives THC and CBD, and our article on THCA, the raw form of THC explains it.

The PubChem entry for cannabidiol and the one for dronabinol, the pharmaceutical name of Δ⁹-THC, give the same formula for both final molecules: C21H30O2. They differ by one ring, which is closed in THC and open in CBD. That small change of shape alters how each molecule fits the receptors.

The CB1 receptor, abundant in the brain, is part of the endocannabinoid system. THC binds to it and activates it, and this produces the cannabis high, the distorted sense of time and the loss of coordination.

Roger Pertwee compiled the affinity measurements in a review published in 2008 in the British Journal of Pharmacology. Depending on the study, the binding constants of THC at the CB1 receptor range from 5 to 80 nanomolar (nM). Those of CBD exceed 4,350 nM, and some measurements find no binding below 10,000. Occupying the same receptor therefore takes at least 50 times more CBD than THC, and CBD does not activate it in the same way.

This difference accounts for the effect and says nothing about any benefit. The CBD sold in shops is not a medicine, and no health claim is authorised for it.

THC activates the CB1 receptor; CBD binds it poorly, tends to dampen its signal and acts on other targets. The liver breaks them down with different enzymes, and both are eliminated slowly.

Sources checked on 20 and 28 October 2026: Stella, Neuron, 2023; Epidyolex SmPC, section 5.2; EFSA, 2025 and 2026. For CBD, the EFSA value covers only supplements of CBD at least 98% pure, and the agency could not establish its safety under 25, during pregnancy or breastfeeding, or with medication; no CBD food is authorised.

Because CBD uses CYP2C19 and CYP3A4, the Epidyolex SmPC describes drug interactions: if you take any medication, talk to your pharmacist.

No, at least at the ratios common in medical and recreational cannabis. In a trial published in 2023, 46 healthy adults who used cannabis occasionally inhaled, double-blind and over four sessions, 10 mg of THC with 0, 10, 20 or 30 mg of CBD. THC alone impaired verbal memory and brought on acute psychotic symptoms. No amount of CBD changed these effects significantly, nor the level of THC in the blood.

For the Conseil d'État, THC is the main psychoactive component of cannabis, liable to cause dependence, and the 0.30% level is not a safety threshold. A full-spectrum product or a CBD-rich cannabis still contains THC, and at the wheel its mere presence in the body is enough to establish the offence. Drogues Info Service answers free of charge and anonymously on 0 800 23 13 13; see also cannabis and mental health.

The French order of 30 December 2021 sets the limit at 0.30% Δ⁹-THC, both for cultivated varieties and for hemp extracts and the products containing them. The sum is simple: 0.30% of 1,000 mg is 3 mg, the cap for a gram of compliant extract. For a flower, the order caps the cultivated variety, and only the batch analysis gives its content. A 2 g bag of hash measured at 0.2% holds 4 mg.

For comparison with illicit cannabis, the French Monitoring Centre for Drugs and Drug Addiction (OFDT) publishes the average potency of seized products. In 2024 it was 14.3% for herb and 29.6% for resin, meaning 143 and 296 mg of THC per gram.

Some products sold as CBD go over 0.30% Δ⁹-THC. A study backed by MILDECA, carried out with Lille University Hospital on 223 samples bought in 2022 and 2023, found 87% of products at less than 0.3% Δ⁹-THC. In 6% of the samples it also found neo-cannabinoids such as HHC or H4-CBD that the label did not mention. Our guide to reading a certificate of analysis shows where the Δ⁹-THC line sits.

The type of extract also sets how much THC can be present. A full-spectrum extract keeps the hemp cannabinoids, THC included, within the limit. A broad-spectrum extract has its THC removed. An isolate is purified CBD without THC or terpenes. Our comparison of full spectrum and isolate covers that choice, and our article on the authorised THC level gives the full legal benchmark.

To the naked eye, a hemp flower cannot be told apart from a high-THC flower, as MILDECA points out. The 4-aminophenol colour test turns pink when THC is about three times less abundant than CBD, blue in the opposite case, and stays inconclusive in between: it measures no content. Only a laboratory analysis quantifies the Δ⁹-THC of a batch; for checking varieties, the 2021 order describes a gas chromatography method. With no rapid test for plants and cuttings, selling plants and taking cuttings remain banned (Conseil d'État, 2025). On a certificate, read the Δ⁹-THC and THCA lines. The sheets in our catalogue show reference profiles, with no laboratory certificate published as of 18 October 2026.

In 2020, in the Kanavape case (C-663/18), the Court of Justice of the European Union held that a member state may not ban CBD lawfully produced in another member state when it is extracted from the whole plant (press release of 19 November 2020). On 29 December 2022, the Conseil d'État annulled the ban on selling raw flowers and leaves, and the 0.30% limit stayed in place.

Status on 28 October 2026: allowed, withdrawn, under discussion

Driving follows another logic. The Cour de cassation ruled on 21 June 2023, and again on 14 November 2023, that driving after using a controlled drug is an offence once use is established, whatever the dose. The authorisation to sell hemp at 0.30% THC at most makes no difference. Under the law of 9 July 2025, the penalty can reach three years in prison and a €9,000 fine, amounts kept by the version of Article L235-1 of the Highway Code in force since 20 August 2026. Our articles on CBD and driving and on the saliva test cover what this means in practice.

Two products containing these molecules are medicines and are not sold in shops. Epidyolex, an oral solution of cannabidiol, is the only authorised CBD medicine. The European Medicines Agency authorised it on 19 September 2019 for seizures linked to Lennox-Gastaut and Dravet syndromes, together with clobazam, and later for tuberous sclerosis complex, from 2 years of age and on prescription.

Medical cannabis contains THC and takes a different route. According to the ANSM page updated on 20 April 2026, the French pilot programme ended on 31 December 2024, and care for patients still being treated has been extended until three months after the Haute Autorité de santé publishes its opinion. Our article on the rollout of medical cannabis tracks its progress.