Three routes to a concentrate that stays under the limit
Concentrating a resin concentrates everything in it, and the regulated fraction is not exempt from that. A plant that was comfortably compliant in the field can yield a concentrate that is not, without anyone having done anything wrong.
That is the whole difficulty, and it has three known solutions. None of them is free: each one costs either yield, aroma, or the accompanying compounds that made the material worth concentrating.
This page sets out the arithmetic, the three routes, and the two very different kinds of limit that an English-language buyer is likely to meet — one expressed as a percentage of weight, the other as milligrams in a container. They are not comparable, and confusing them is the commonest error here.
⚠️ Scope. This page describes composition, processes and documents. It does not describe what a product does to a person, gives no amounts, and does not replace a healthcare professional or a solicitor.
The arithmetic the question turns on
Concentration multiplies everything
If a process takes ten kilograms of plant material down to one kilogram of resin, whatever was in the starting material is now roughly ten times more concentrated. The separation is mechanical or solvent-based; it does not select against one cannabinoid.
Compliant input does not imply compliant output
This is the sentence that surprises people. A crop within the agricultural threshold can produce a concentrate several times above it, and the arithmetic alone explains why.
Why the ratio survives concentration
Because both cannabinoids ride the same fraction. Resin glands contain both, so collecting glands collects both in something close to their original proportion.
What that leaves as the only levers
Change what goes in, remove one component afterwards, or build the product from a purified starting material. Those are the three routes, and there is not a fourth.
The factor 0.877, and why it is fixed
What the acid form is
In the living plant the cannabinoids exist mostly in acid form, carrying an extra carboxyl group. THCA is the acid form of delta-9-THC.
What heat does to it
Heating removes that group as carbon dioxide, converting the acid form into the neutral one. The process is called decarboxylation and it happens gradually with time as well as quickly with heat.
Where the number comes from
It is the ratio of the two molecular masses. The acid form is heavier by the mass of what it loses, so one unit of THCA yields about 0.877 units of THC.
Why the sum is what counts
Because the material will be heated at some point, and the limit applies to what is there afterwards. A figure quoting only the neutral form has omitted the part that arrives later.
The formula in one line
Total THC equals delta-9-THC plus THCA multiplied by 0.877. Every comparison on this page uses that figure and no other.
Route one: the plant itself
Cultivars with a different ratio
Breeding has produced varieties in which the enzymatic pathway favours one cannabinoid heavily over the other. Starting material of that kind concentrates to a lower figure because it began lower.
Why this route is limited
The ratio is a property of the plant, not of the batch, so it caps how far the route can go. It reduces the starting figure; it does not remove anything.
What it costs
Choice. The grower is confined to the cultivars that carry the trait, which means giving up whatever aromatic profiles the others would have supplied.
Where it works best
For mildly concentrated products, where a low starting figure survives the multiplication. Beyond a certain concentration factor the arithmetic overtakes the genetics.
Route two: the purification step
What is added to the process
An additional separation after extraction — most often chromatographic — designed to pull one cannabinoid out of the mixture while leaving the rest.
Why it is technically demanding
The two molecules are structurally close, so the step has to resolve compounds that behave similarly. That is why it is a specialist operation rather than a routine one.
What the result is called
Broad spectrum, in trade usage: the accompanying compounds retained, the regulated one removed. The term has no legal definition, which is why the certificate has to be read rather than the label.
What it costs
Money, yield, and part of the aromatic fraction. Nothing that selective is free, and some of what is lost is exactly what the buyer was paying for.
Route three: starting from an isolate
What an isolate is
A crystalline powder of a single cannabinoid, typically above 99 per cent, with the rest of the plant removed at an earlier stage.
Why the question disappears
Because there is nothing left to concentrate. A product built from isolate contains what was deliberately put into it, and the regulated fraction was never among the ingredients.
What it costs
Everything else. No terpenes, no minor cannabinoids, no aroma. The product becomes an ingredient list rather than a plant extract.
Why it is nonetheless common
Predictability. A powder weighs, mixes and stores like any raw material, and batch-to-batch variation nearly disappears — which matters more to a manufacturer than to a buyer.
What “not detected” is a statement about
Every method has a floor
A laboratory can only report down to the lowest concentration its method reliably measures. Below that it reports an absence, because it has nothing to report.
Two limits, often confused
The limit of detection is the point below which presence cannot be distinguished from noise. The limit of quantification is the higher point below which a number cannot be assigned with confidence.
Why this makes the phrase relative
A result of “not detected” means “not detected by this method”. Another laboratory with a lower limit, running the same material, may return a figure.
What follows for the label
An absence on a report is a property of the analysis, not of the substance. A report that states no limit of quantification has withheld the number that gives the absence its meaning.
The practical consequence
Two products both described as free of the regulated fraction may differ by an order of magnitude in what is actually present. Without the stated limit, the page cannot show the difference.
Two limits that are not the same kind of number
The percentage limit
Expressed as a share of weight. It scales with concentration: multiply the material tenfold and the percentage stays the same only if the two components multiply together, which is what happens.
The absolute limit
Expressed in milligrams of the controlled substance per container. In the United Kingdom, the exempt product provisions of the Misuse of Drugs Regulations 2001 set that figure at one milligram, alongside two further conditions.
Why the two do not translate
A percentage says nothing about a container until the container size is known. A container limit says nothing about a material until the fill weight is known. Neither converts into the other without a second number.
The consequence that catches sellers out
A product with a reassuring percentage can exceed an absolute limit purely because the bottle is large, and a smaller bottle of the identical material can pass. Packaging decides it, not chemistry.
What a buyer can do about it
Ask for total THC in milligrams per container as well as the percentage. A seller who works in this market will have the figure, because the market requires it of them.
Where a certificate fails on this question
Only the neutral line reported
A report showing delta-9-THC and no acid form has given half the sum. The missing line is the one that converts on heating.
No limit of quantification stated
Then “not detected” is unquantified. It could mean a very small figure or a much larger one, and the document does not distinguish them.
Batch not identified
A certificate for the product line covers no particular material. On a question decided by arithmetic on specific numbers, the wrong batch is as unhelpful as no batch.
Percentage without a mass
Where the applicable limit is absolute, a percentage on its own cannot be checked against it. The container weight has to appear somewhere, and often it does not.
An old date
Acid forms convert slowly at room temperature. A figure measured long ago describes a distribution between the two forms that has since shifted, even though the sum is stable.
What “free of THC” means on a package
It is not a defined term
No regulation attaches a number to it in this category. It functions as a summary of a laboratory result, and different sellers summarise different results the same way.
What it usually rests on
A report of “not detected” at the laboratory’s own limit. That is a legitimate basis for the phrase and a weak one, since the limit is not stated on the package.
Why the phrase persists
Because it answers a question buyers genuinely have, in four words. The problem is not the intention but the precision.
What to ask instead
The figure and the limit of quantification. Two numbers instead of a phrase, both of which appear on a proper report.
A worked example, step by step
The starting material
Take flower measured at 0.15 per cent total THC — comfortably within the agricultural threshold in most of the European Union.
The concentration
Suppose the process yields one part resin from eight parts flower, and that the cannabinoids follow the resin fraction rather than staying with the plant matter.
The arithmetic
Roughly 0.15 multiplied by eight, giving about 1.2 per cent in the concentrate. Nothing has been added and nothing has gone wrong; the figure moved because the denominator shrank.
The same material in a container
Ten grams of that concentrate carries around 120 milligrams of total THC. Against an absolute limit of one milligram per container, the gap is not marginal.
What the example demonstrates
That the two limits fail differently and at different points. A material can clear one comfortably while missing the other by a factor of a hundred.
Why the ratio is largely fixed in the plant
A shared precursor
Both cannabinoids derive from the same precursor compound, and separate enzymes convert it down one path or the other. The proportion is set by which enzymes the plant expresses.
Why cultivation cannot move it much
Light, feeding and timing shift the total amount produced far more than the ratio between the two. The split is genetic.
What breeders can do
Select for plants whose enzymatic balance is heavily weighted one way. This is a slow process measured in generations, and it has limits.
Why this constrains route one
Because the grower inherits a ratio rather than choosing one. It can be improved, but not set to an arbitrary value.
Why not everyone takes the isolate route
It removes what was being sold
The accompanying compounds are the reason a plant extract commands a price above a synthesised ingredient. Removing them removes the argument for the product.
Aroma disappears entirely
A pure crystalline powder has no smell. Reconstructing one means adding terpenes back, which is a different product with a different label.
The price does not always fall
Isolate is cheap per unit of active content but expensive in what has to be added afterwards to make a credible product. The saving is smaller than it looks.
Where it remains the right answer
Where the applicable limit is absolute and strict, where exact content matters, and where consistency between batches is worth more than character.
How to compare two offers here
Compute both sums
Delta-9 plus THCA times 0.877, for each product. Compare the results, not the headline percentages.
Convert to milligrams per container
Multiply by the net weight. This is the only form in which an absolute limit can be checked.
Read the limit of quantification
Where either report says not detected, the limit is the number that gives the statement content. Without it the two reports are not comparable.
Check the batch numbers match
Against the packaging, in both cases. Everything above is arithmetic on figures that have to belong to the material in front of you.
Ask which route was taken
Genetics, purification, or isolate. The answer explains the price and predicts what the product will smell like before it is opened.
What the certificate has to show
Both THC lines
Neutral and acid form, separately, so the sum can be computed rather than assumed.
The limit of quantification
Stated as a number, for each analyte. It is what turns an absence into information.
The batch number and date
Matching the packaging, recent enough to describe the current state of the material.
The laboratory identity
Name, and accreditation where it exists. An unattributed table is a table.
The contaminant panel
Concentration concentrates pesticides and heavy metals along with everything else, which is exactly why this panel matters more for a concentrate than for a flower.
The concentration factor, and how to find it
What the number is
The ratio between the mass that went in and the mass that came out. Eight kilograms of flower yielding one kilogram of resin gives a factor of eight.
Why sellers rarely publish it
Because it is a production figure rather than a product figure, and because a low yield reads as inefficiency to anyone unfamiliar with what a narrow selection costs.
How it can be inferred
By comparing the cannabinoid content of input and output, where both are known. The ratio between the two figures approximates the factor, since the cannabinoids largely follow the resin.
Why the approximation is rough
Some material is lost at every stage, and not all of it is lost evenly. The inference gives an order of magnitude rather than a precise multiplier.
What it is useful for anyway
Sanity-checking a claim. A product described as a heavy concentrate, reporting a figure close to that of flower, is asserting something the arithmetic does not support.
Where measurement uncertainty enters
Every figure has a range
A laboratory result is an estimate with a stated uncertainty, not a point. Competent reports say so; the value is accompanied by a plus-or-minus.
Why it matters near a limit
A result close to the applicable figure may straddle it once the uncertainty is applied. The reported number alone does not settle whether the material is within the limit.
What a careful seller does
Leaves margin. Working to a figure comfortably below the limit rather than to the limit itself is how a producer absorbs the uncertainty rather than passing it to the buyer.
Why this argues against the tightest possible tolerance
A batch engineered to sit exactly at the threshold will cross it in half the analyses of it. Margin is not caution; it is the only way to get a repeatable answer.
The exempt product rule has three conditions, not one
The milligram is the famous one
No more than one milligram of any controlled drug per container. It is the condition that gets quoted, because it is a number and numbers travel.
The product must not be designed for administration
That is, not designed for the administration of a controlled drug to a person. A product formulated around the regulated fraction fails here regardless of quantity.
The drug must not be readily recoverable
It cannot be capable of being recovered by readily applicable means in a quantity that poses a risk to health. This condition constrains the format as much as the content.
All three apply together
Meeting the milligram figure alone is not sufficient, and a discussion that mentions only that figure has described a third of the rule.
Why this belongs on a page about concentrates
Because a concentrate is, by construction, the format in which small quantities become recoverable quantities. The condition bites hardest exactly here.
A short glossary
Total THC
Delta-9-THC plus THCA multiplied by 0.877. The figure that limits are written against.
Decarboxylation
The loss of a carboxyl group under heat, converting the acid form into the neutral one.
Limit of detection
The lowest concentration at which presence can be distinguished from background noise.
Limit of quantification
The lowest concentration at which a method can assign a reliable number. Higher than the limit of detection, and the more useful of the two.
Broad spectrum
Trade term for an extract retaining the accompanying compounds with the regulated one removed. No legal definition attaches to it.
Isolate
A single cannabinoid in crystalline form, typically above 99 per cent, with the plant removed earlier in the process.
Exempt product
A United Kingdom regulatory category with three cumulative conditions, one of which is a maximum of one milligram of any controlled drug per container.
The five checks that apply to any product
The batch certificate
Request it with the number printed on the packaging. A general document for the product line does not cover this batch, and those differences are exactly what it should record.
Total THC
Delta-9-THC plus THCA multiplied by 0.877, because THCA becomes THC under heat and the limit applies to the sum, not to either value alone.
Price per milligram
A division, not an opinion. The only figure that makes two products comparable, whatever the format, purity and pack size.
The claims
Without an authorisation number in the EU Register these are assertions, not data — and for cannabidiol that register contains no authorised entry to this day.
The seller’s details
Company name, address and contact. Without them there is also no counterparty to turn to if something turns out to be wrong.
How this connects to the rest
With the extraction processes
All of them concentrate. The route chosen changes yield and character, and none of them changes the arithmetic on this page.
With winterisation
It removes waxes, not cannabinoids. It is a purification step, but not the one that answers this question.
With distillate and isolate
The third route is the isolate, described there in terms of what nine percentage points contain. Here it appears as the answer that costs the most.
With the country pages
The applicable limit, its form and its number are national. This page gives the arithmetic; those pages give the figure to compare it against.
What this is for in practice
Facing a certificate
Find both THC lines, add them with the factor, and look for the stated limit of quantification. Three things, in that order.
Facing a claim of absence
Read it as a laboratory result, not a property of the material, and ask what the limit was.
Facing a large container
Convert the percentage to milligrams before assuming a reassuring figure carries across. Where the limit is absolute, container size is part of the answer.
What this page publishes
Processes, verifiable documents and arithmetic. No promises of effect — for that, the EU Register contains no authorised entry.
Frequently asked questions
Can a concentrate contain no THC at all? Not in the sense of absolute zero, which no analysis can demonstrate. It can be built from an isolate, in which case the regulated fraction was never an ingredient, and reports will read as not detected at the laboratory’s limit.
Why does a compliant plant give a non-compliant resin? Because concentration multiplies both cannabinoids together. The percentage rises with the concentration factor even though the proportion between them is unchanged.
What is the 0.877 factor for? It converts the acid form to the neutral one by mass, because heating removes a carboxyl group. Without it the sum understates what will be present after any heating step.
Is broad spectrum legally defined? No. It is a trade description for an extract with the regulated fraction removed by an additional step. The certificate settles what a given product actually is.
Does not detected mean zero? No. It means below what this method measures, and different methods have different floors. The stated limit of quantification is what gives the phrase a size.
Why do percentage limits and container limits give different answers? Because they measure different things. A percentage is a share of weight; a container limit is an absolute quantity. Converting between them requires the net weight, which is not always printed.
Which route is best? It depends on which limit applies and what the product is for. Genetics is cheapest and most limited, purification preserves the most character, isolate is the most certain and the most stripped.
Can cultivation reduce the THC in a plant? Only marginally. Growing conditions move the total quantity of cannabinoids far more than the ratio between them, which is set genetically.
Does an old certificate still apply? The sum is stable, but the split between acid and neutral forms shifts slowly at room temperature. For a question decided on the sum this matters less than the batch number matching.
Why is the contaminant panel more important for a concentrate? Because concentration applies to contaminants as well. A pesticide residue at an acceptable level in flower can be multiplied several times over in the resin drawn from it.
What we check and what we do not
We check what can be checked from documents: official registers, declared contents, certificates of analysis, divisions. We do not test products, do not produce rankings and do not claim any effect.
On this subject nearly everything reduces to arithmetic on numbers that a laboratory produced. That is unusually solid ground, provided the numbers are all present — and the missing line is more often the limit of quantification than the cannabinoid itself.
What we cannot do is tell you whether a given figure is lawful where you are. The form of the limit differs between markets, and only the country pages carry the figure that applies.