Buying CBD oil in the UK: what the label has to prove
If you take one thing from this page: the percentage on the label is not a way to compare two oils. A 30 ml bottle at 10 % for £75 costs half what a 10 ml bottle at 5 % costs for £25 — per milligram. On the shelf it looks three times dearer.
That is not a sales trick. It is arithmetic, and it is the most expensive mistake you can make buying CBD in Britain.
There is a second thing, and it is specific to this market: Great Britain runs a public list of CBD products linked to novel food applications. No other European market we cover has one. Whether a product is on it is a fact you can check before you pay.
The division that decides everything
One calculation, the same for everyone.
The formula
Volume in ml × strength percentage × 10 = total CBD in milligrams.
Then: price divided by that number. That is the whole method.
Two bottles side by side
| Bottle A | Bottle B | |
|---|---|---|
| Volume | 10 ml | 30 ml |
| Strength | 5 % | 10 % |
| Total CBD | 500 mg | 3000 mg |
| Price | £25 | £75 |
| Price per mg | £0.050 | £0.025 |
The bottle that looks dearer costs half. Not because it is a cheaper brand, but because it holds six times the active substance for three times the price.
Why almost nobody shows that number
Because once the division is done, most packs look bad. Small bottles sell a little at a high price and the percentage hides it.
A shop that publishes price per milligram unprompted is telling you something: it is not afraid of the comparison.
The one condition
That the route is the same. Comparing capsule milligrams with sublingual oil milligrams is measuring two different things with one unit — and the difference between routes is larger than the difference between most brands.
The FSA public list
This is the part that has no equivalent in any of our other fifteen markets, and it is worth using.
What it is
Ingestible CBD products came under the novel foods regime in Great Britain, and the Food Standards Agency maintains a published list of products linked to applications that are being assessed.
What it does and does not tell you
It tells you that a product entered a regulatory process. It is not a safety approval, not an endorsement and not a statement that the label is accurate.
Why it is still worth checking
Because it is a public, verifiable fact about a specific product — and in a market where almost every other claim comes from the seller, a fact that does not come from the seller is worth having.
Where it fits in the order of checks
After the certificate, not before. A product on the list without a batch certificate is still a product whose contents nobody has shown you.
The certificate of analysis
Without it, no number on the box is verifiable — not the percentage, not the THC content.
The batch number
The number on the certificate has to be the number on your bottle. A brand-level analysis, or one from a previous harvest, describes something else.
It is the first check and the one most products on the market fail — not because they are poor, but because a brand-level analysis only has to be paid for once.
The laboratory name
With a name, and not the seller’s. «Lab tested» without a laboratory commits nobody to anything: every product was tested by somebody at some point.
The cannabinoid profile
Numbers, not ticks. A serious certificate shows at least this:
| Row | Why you look at it |
|---|---|
| CBD | What you are paying for |
| CBDA | Acidic form; total CBD counts it in |
| Δ9-THC | Decides legality and any saliva test |
| CBG, CBN | Profile portrait; high CBN means age, not quality |
The contaminants
Heavy metals, pesticides, residual solvents. Hemp takes up efficiently from the soil whatever is in it — a property used even for land remediation. What is good for the ground is bad news in an extract.
The date
Cannabinoids degrade with light, heat and oxygen. A certificate is a photograph of one batch on one day; older than the product’s shelf life, it does not describe what you received.
Total CBD and the 0.877 factor
The plant does not make CBD
It makes CBDA, cannabidiolic acid. The acidic form is what is actually present in the living flower; the neutral form appears with heat.
What the heat does
The carboxyl group leaves as carbon dioxide, and it has mass: 1 mg of CBDA yields 0.877 mg of CBD.
The correct sum
Total CBD = CBD + (CBDA × 0.877).
Adding the two rows straight gives a figure higher than the real one — and therefore a price per milligram that looks lower than it is. The error always runs the same way, and always in the seller’s favour.
Full spectrum, broad spectrum and isolate
Full spectrum
The extract keeps the plant’s other cannabinoids and terpenes, including THC in traces.
Broad spectrum
The same starting point, with an additional step that removes the THC. Whether it actually was removed is shown only by the batch certificate.
Isolate
Cannabidiol alone, usually above 99 %. No terpenes, no other cannabinoids, no THC by construction.
When the difference is practical
If a workplace or roadside test is a possibility, isolate closes the question by design. Broad spectrum works if the certificate confirms the absence with a number, not with the words «THC free» printed on a box.
Otherwise it is a matter of taste and price, not quality: the three profiles differ in composition, not in value.
The milligrams on the label are not the ones that arrive
Swallowed
Everything swallowed passes through the gut and then the liver before reaching the blood. Published pharmacokinetic studies place oral bioavailability at around 6 %.
From a 25 mg capsule, roughly 1.5 mg reaches the circulation.
Held under the tongue
Absorbed partly through the oral mucosa, bypassing the liver first: studies place it between 13 and 19 %.
The catch is behavioural: the figure assumes the oil stays there for a minute or more.
With a fatty meal
CBD is fat-soluble. The product information for the only CBD medicine authorised in the EU describes an increase in exposure of the order of four to five times with a high-fat meal compared with fasting.
Same product, same amount swallowed, four times the difference depending on whether there was breakfast.
What the front of the box is allowed to say
«Lab tested»
On its own, nothing. It commits to no laboratory, no batch and nothing about what was measured.
«Organic»
Real, and regulated: it requires an accredited control body and a code on the label. It certifies the farming — nothing about extraction or CBD content.
«Premium», «pure», «natural»
None has a legal definition for CBD products in any of our markets. «Pure» is the most misleading, because it sounds like a purity figure without being one.
And what it is not allowed to say
What the product is for. There is no authorised health claim for cannabidiol in Great Britain or in the European Union — which is why the front of the box carries a percentage, an adjective and a photograph, and nothing else.
If you take prescription medicines
The same enzymes
CBD is metabolised in the liver by cytochrome P450 enzymes, chiefly CYP3A4 and CYP2C19. Those same enzymes handle a very wide share of everyday prescriptions.
The mechanism in one sentence
When two substances compete for the same enzyme, one waits. The one that waits accumulates in the blood above the level its dose was calculated for — and it works in both directions.
The grapefruit comparison
The grapefruit juice warning on some patient leaflets exists because of CYP3A4. Same enzyme, same reason. Nobody thinks grapefruit is dangerous, and the warning is there anyway.
Who to ask
The pharmacist. Not us, not a forum, not the shop. They have your list and find the interaction in seconds. It is the only question on this page whose answer is not ours to give.
What EFSA said in February 2026
The European Food Safety Authority published an updated opinion: the safety of cannabidiol as a novel food could not be established, and it derived a reference value of 0.0275 mg per kilogram of body weight per day.
For a 70 kg adult that is roughly 2 mg a day — well below what most labels suggest. It is neither a ban nor a recommendation: it is a benchmark nobody has publicly compared against the contents of the bottles on the shelf.
Britain sets its own food policy since leaving the EU, but the underlying data is the same body of evidence, and no UK figure contradicts it.
Strength: what the percentage tells you and what it hides
Shelves run from 5 % to 40 %, and the bigger number is not automatically the better buy.
What it measures
What share of the liquid is CBD. A 20 % oil is twice as concentrated as a 10 % one — half the drops for the same milligrams.
Why it does not settle the price
Because price per milligram depends on volume and strength together. 40 % in 10 ml holds 4000 mg; 10 % in 30 ml holds 3000 mg. Choosing between them is a price decision, not a strength one, and it only shows after the division.
When high strength genuinely helps
When you want to handle less liquid: fewer drops, less taste, a smaller bottle. That is convenience, not quality.
When it works against you
Because per-drop precision gets coarser: if one drop carries 40 mg instead of 10, half a drop is a 20 mg difference. That is an observation about measurement, not advice about amounts.
A drop is not a unit
What a drop actually is
Whatever hangs from the pipette until gravity wins. That moment depends on the opening and on the thickness of the carrier oil — two things that vary by product and appear on no label.
The assumption everyone repeats
«20 drops per ml» is roughly true for water. CBD oil is not water. The figure is used because it is convenient, not because it was measured.
What helps instead
A pipette marked in millilitres. Millilitres are identical across products; drops are not. With 0.5 ml of a 10 % oil you calculate straight to 50 mg.
The carrier oil
What else is in the bottle
CBD is not sold neat. It is dissolved in a carrier, usually MCT (fractionated coconut oil), hemp seed oil or olive oil.
What the carrier decides
Taste, shelf life and how even the drops are. It also explains why two bottles of the same strength can deliver different milligrams per drop.
Where the confusion comes back
Hemp seed oil is a perfectly good carrier and a perfectly good food oil. Sold as the main product under a CBD-sounding name, it is something else entirely — recognisable by what is missing: no percentage, no milligrams, no certificate.
Storage
Why the glass is dark
Light, heat and oxygen break cannabinoids down, and THC converts to CBN. Amber or violet glass is a filter, not a design choice.
The whole rule
Cool, dark, tightly closed. A bottle that spent a year above the hob is not the bottle its certificate describes — and nothing on the packaging says so, because the packaging was printed the day the product left the factory.
What a high CBN reading means
Not that the product is bad, but that it is not fresh. CBN is not an added ingredient: it is what THC becomes.
What the British market looks like right now
Shops at the top, two institutions below them
Of the ten organic results for this search, most are retailer category pages. The two text pages are the Boots health hub and BBC Good Food — both large British institutions, and neither selling the product in that article.
What that means for what you read
That the highest-authority British writing on this subject comes from a pharmacy chain and a food magazine. Both answer the health questions better than we do, and they are named here so you can go to them.
What is missing
An independent page that shows you how to put two products side by side. That one does not exist — which is why we write about the arithmetic rather than the effects.
Ten seconds before you buy
- Is there a batch certificate, and does the number match the bottle?
- Does the laboratory have a name that is not the seller’s?
- Does the cannabinoid profile carry numbers rather than ticks?
- Is the date inside the product’s shelf life?
- Can you work out the price per milligram from what is published?
If any answer is no, the other four do not make up for it.
What this page will not tell you
Not what it does
Because there is no authorised health claim for cannabidiol in Great Britain or the European Union. Not one — and the questions Google attaches to this search, about pain and sleep, are exactly the ones no page is permitted to answer.
Not how much to take
That question belongs with a healthcare professional, and the European position is that the safety of regular oral consumption has not been established.
Not which brand is best
We tell you which products the arithmetic can be done on, and which it cannot. A ranking will follow when we have our own price-per-milligram measurements across successive batches, with the date and method beside them.
Frequently asked questions
How do I compare two CBD oils? By price per milligram: volume in ml × percentage × 10 = total CBD in mg, then price divided by that figure. The percentage is a concentration, not a quantity and not a price.
What is the FSA list and does it mean a product is approved? It is a public list of CBD products linked to novel food applications under assessment. It shows a product entered a process; it is not a safety approval and says nothing about label accuracy.
Is hemp seed oil the same as CBD oil? No. Hemp seed oil is pressed from the seed and contains almost no cannabinoids, because the seed is not where the plant makes them.
Full spectrum or isolate? Neither is better — they are different. Isolate contains no THC by construction, which matters if a test is a possibility.
What is the THC limit in the UK? The figure and the date we last checked it are on our UK legal page. Numbers from German or Austrian articles — the 0.3 % limit in particular — do not apply here.
Why don’t you say what CBD does? Because there is no authorised health claim for cannabidiol, and because EFSA was unable to establish the safety of regular oral consumption.