CBD vs THC: what is the difference?

Both form in the hemp flowers and share one formula: C₂₁H₃₀O₂ — 21 carbon atoms, 30 hydrogen and 2 oxygen. The difference is in how they are joined: in THC the atoms close an extra ring, while in CBD that ring stays open.

In the plant both appear first as acids — CBDA and THCA — and turn into CBD and THC when heated. How much of each a plant makes depends on the variety: industrial hemp, the source of the CBD sold in the EU, makes a lot of CBD and very little THC, while cannabis varieties grown for their flowers make a lot of THC.

The differences that matter to a buyer, in one table.

The “high” comes from activating the CB1 receptors in the central nervous system. THC fits these receptors and activates them directly. CBD has a very weak affinity for them and does not activate them in the same way, which is why a product made from industrial hemp does not produce that state.

In 2018 the World Health Organization's Expert Committee on Drug Dependence reviewed cannabidiol and concluded that, in its pure form, it shows no signs of abuse or dependence potential. On that basis CBD is not controlled under the 1961 UN Single Convention, and in 2020 the Court of Justice of the EU confirmed that it is not a narcotic drug.

The royal decree of 6 September 2017 on narcotics prohibits growing cannabis except under the EU farm rules of Regulation (EU) 2021/2115, which admit varieties with at most 0.3 % THC. According to VAD, since 1 June 2024 cannabis falls on the list of controlled substances only when it holds more than 0.3 % THC; the limit used to be 0.2 %.

Hence a common mix-up: “legal hemp” does not mean “THC-free” but “below the limit for the plant”. Food has far lower THC limits, and for a finished oil or cream we found no separate numerical limit, so the figure that counts is the one on the batch report. More in Is CBD legal in Belgium?

Drug tests look for THC and the compound the body turns it into, THC-COOH — not for CBD. Belgium's road traffic law (Art. 37bis) names THC, not CBD, too. Isolate and broad-spectrum extract should contain no detectable THC. Full spectrum holds traces: small, but not zero, and with regular use of large amounts a build-up cannot be ruled out.

In sport the rule is spelled out: CBD is not on the World Anti-Doping Agency's (WADA) prohibited list, but THC is banned in competition. A full-spectrum product can therefore put an athlete in trouble.

If you are tested at work, at the wheel or in sport, choose isolate or broad spectrum and check that the batch report shows THC as “not detected” — even then nobody can promise the result of a test.

On the label, the CBD–THC difference shows up as the extract type. Check it, then confirm on the lab report how much THC your batch has; products in the catalogue carry their report on their page.

Which option is “better” is not for us to decide. The choice between the three comes down to composition and your own situation — an upcoming test, for example.

• Full spectrum — keeps the hemp's other compounds too, including traces of THC.
• Broad spectrum — keeps the other compounds, but the THC is removed.
• Isolate — purified CBD, with nothing else from the plant.