The 850mg Problem: What a Potency Shortfall Tells a UK Buyer About Everything Else a Brand Does

A bottle carries a confident figure on the front: 1000mg of CBD. The certificate of analysis for that batch, once located and read, gives 850mg. The instinct is to treat this as a dosing inconvenience, a small matter of a few milligrams missing from a dropper. The more useful instinct is to treat it as a diagnostic. Fifteen per cent is not a rounding artefact. It is a signal that something in the manufacture, the release testing or the label arithmetic was not under control, and the interesting question is which.

A shortfall is a symptom, not a diagnosis

The causes divide into four families. Label arithmetic that was wrong before any oil existed. Process failures in decarboxylation, mixing or filling. Change over time between the test date and the purchase date. And, occasionally, a deliberate gap between what a marketing team wanted to claim and what a production team could deliver. Each produces the same symptom and calls for a different set of questions.

Arithmetic failures that happen before a drop is bottled

Percentage declarations are ambiguous. Ten per cent weight-for-volume in a 10ml bottle gives roughly 1000mg, because MCT carrier sits near 0.94 g per millilitre. Ten per cent weight-for-weight gives approximately 940mg. The two conventions are both in use and rarely stated. A brand that has not settled this internally will struggle to settle it on the label.

Then there is the question of what is being counted. A certificate may report CBD, CBD plus CBDA, or total cannabinoids. The conversion is not one to one: CBDA has a higher molecular weight, and the factor for converting CBDA to its decarboxylated equivalent is roughly 0.877. A brand reporting total cannabinoid mass as though it were CBD is overstating by a margin that grows with the amount of acid form left in the oil.

Finally, units. Milligrams per bottle, per millilitre and per drop are three different claims, and drop size is the loosest of them. A nominal 0.05ml drop delivered from a glass pipette can plausibly range from 0.03ml to 0.06ml depending on viscosity, angle and the user's hand. A per-drop figure is an average presented as a fact.

Decarboxylation decides the number

Raw hemp contains mostly CBDA. Heat converts it to CBD, releasing carbon dioxide, and the completeness of that conversion is the single largest determinant of the potency a certificate will later show. Under-convert and the CBD figure falls short of the target; overheat and CBD begins degrading, with CBN appearing as a marker of stress. A brand that publishes a COA showing CBD and CBDA separately, with a stated total, is a brand that understands its own process. A brand that shows one number with no method note leaves the reader guessing which of these it published.

Mixing, filling and the sampler's thumb

CBD is only moderately soluble in medium-chain triglyceride oil, and solubility improves with warmth. Warm filling followed by cooling can produce crystallisation or stratification, and a sample drawn from the top of a tank will not represent the bottle at the bottom. Homogeneity is a genuine engineering problem, and the sampling plan is the evidence that it was addressed. Ask where the sample was taken from. A vague answer here is itself an answer.

Certificates age faster than oil

The test date is not the purchase date. Between release and the end of a twelve or twenty-four month shelf life, CBD oxidises slowly and light and heat accelerate the process. A few per cent of loss is unremarkable. A fifteen per cent gap between the release certificate and the retail unit is not something degradation alone usually explains, and a shortfall present at release cannot be attributed to time at all.

Why fifteen per cent should trouble you more than it looks

A release specification with a tolerance of plus or minus ten per cent is ordinary practice. A product at 850mg against a 1000mg label sits outside that band. Either the specification was not applied, or it was written loosely enough to be meaningless, or the test was performed on a sample chosen to flatter. None of these possibilities is confined to potency. The same quality system governs pesticide screening, heavy metals, microbiological testing and residual solvents, none of which a buyer can assess at home. Potency is simply the one number visible enough to be checked against a claim.

The legal backdrop matters here too. The Consumer Protection from Unfair Trading Regulations 2008 address misleading commercial practices, and the advertising codes require that objective claims be substantiated. Trading Standards can act on a label that overstates a quantity, and the same label will be scrutinised when it touches regulated territory such as THC content, where the advisory intake limit the FSA applies in novel food assessments leaves very little room for error.

What a well-run brand does when it misses

It withdraws or reworks the batch. It publishes a deviation note explaining the cause and the corrective action. It re-tests and reissues a certificate with a date and a batch number that match the bottles actually sold. It does not quietly delete the old certificate, reissue a new one against a different sample, and let the stock remain on shelves. How a brand behaves after a shortfall is more informative than any claim on its homepage.

Five questions to put to any high-strength claim

Is the certificate for the batch number printed on the bottle, and is it recent? Does it report CBD and CBDA separately alongside a total, and state the basis in milligrams per bottle or per millilitre? Was the sample drawn from finished retail units rather than bulk? Was the analysis performed by a laboratory accredited to ISO/IEC 17025 for that method, with the LOQ disclosed? And does the brand publish a potency specification with a stated tolerance, so that a result can be judged against something other than hope?

Potency is one number, control is a system

A 150mg shortfall is unlikely to harm anyone. That is not the objection. The objection is that potency is the most testable claim a CBD brand makes, and a brand that cannot meet it reliably is unlikely to be meeting the ones nobody can check at the kitchen table. Purity is not a feeling about a bottle. It is a series of controlled steps, documented, and a number that holds up when someone looks.