Published 21 October 2026 · Last updated 21 October 2026
Extract Ratios · Silymarin · How To Compare
Milk Thistle Explained: What "4000mg" Actually Means
Almost every milk thistle product in Britain has a big number on the front. Almost none of them tell you the one figure that lets you compare two of them. Here is the arithmetic, and the question to ask any seller.
The Short Version
"4000mg" is almost never 4,000mg of anything in the tablet. It is the raw seed the extract was derived from. A 40:1 extract means 100mg of extract came from about 4,000mg of seed.
The figure that matters is silymarin. It is the marker compound milk thistle extracts are standardised by, and it is the only number that compares two products honestly.
Do this sum: extract weight × standardisation percentage = milligrams of silymarin. 100mg at 80% is 80mg.
If no extract ratio is stated, it is almost certainly ground seed rather than an extract — and ground seed carries only a few percent silymarin.
What milk thistle is
Silybum marianum is a tall purple-flowered thistle native to the Mediterranean and now naturalised across much of Europe, including Britain. It has been recorded in European herbal practice for well over two thousand years — Dioscorides described it in the first century AD.
Supplements are made from the seed, not the leaf or the aerial parts. The seed contains a group of related compounds collectively called silymarin, of which the individual constituents include silibinin, silychristin and silydianin. Silymarin is what extract manufacturers assay and standardise to, and it is why "80% silymarin" appears on better labels.
That distinction — seed versus whole herb, extract versus ground powder, standardised versus unstandardised — is where almost all the difference between products on a UK shelf actually sits. The milligram figure on the front tells you very little about any of it.
The arithmetic behind the big number
An extract ratio describes how much raw material went into the process for each part that came out. A 40:1 extract means roughly forty parts of dried seed produced one part of extract. So 100mg of a 40:1 extract is derived from about 4,000mg of seed — and that is the number that ends up on the front of the tub.
It is a legitimate and completely standard way to express an extract. The problem is only that it describes what went into the process, not what came out of it — and two 40:1 extracts from different manufacturers can differ substantially in what they actually contain.
So ask for the standardisation
A standardisation percentage tells you how much of the extract is the marker compound. Commercial milk thistle extracts are sold at 30%, 50%, 70% and 80% silymarin. Plain ground seed, with no extraction at all, typically carries only a few percent.
Multiply the extract weight by that percentage and you have the figure to compare. It is the only sum worth doing.
Here is what that does to four products that all say the same thing on the front:
| Label says | What is in it | Standardisation | Silymarin per tablet |
| "4000mg", no ratio stated | 4,000mg ground seed | None | Not stated — often only a few percent |
| "4000mg", 40:1 extract | 100mg extract | 30% silymarin | 30mg |
| "4000mg", 40:1 extract | 100mg extract | 70% silymarin | 70mg |
| "4000mg", 40:1 extract | 100mg extract | 80% silymarin | 80mg |
Identical front-of-pack number in all four rows. The top row is the one to watch. An extract ratio is a selling point — nobody who has one leaves it off a label. So where no ratio is stated, the sensible assumption is ground seed.
Six questions to ask about any milk thistle product
1. Is an extract ratio stated? 40:1, 20:1, 4:1, or nothing. No ratio means ground seed, which is a legitimate product but is not comparable on milligrams with an extract.
2. What is the silymarin standardisation? A percentage. This is the question most sellers cannot answer, and the answer tells you more than anything else on the label.
3. What does that come to in milligrams? Extract weight times percentage. Do the sum yourself rather than trusting the headline.
4. Which part of the plant? It should say seed. Aerial parts and whole-herb material carry far less silymarin.
5. Is the species named? Silybum marianum. Blessed thistle (Cnicus benedictus) and holy thistle are different plants and are sometimes confused with it.
6. What is the stated serving? Per-tablet figures mean nothing until you know how many you are meant to take. A 100mg tablet taken three times a day is three times a 100mg tablet taken once.
Those six questions work on any seller, ours included. If a product page cannot answer them, that is itself the answer.
No Authorised Claims Does Not Mean No Research
You will notice this guide tells you nothing about what milk thistle does. That is not because nothing is known — milk thistle is one of the most studied botanicals in the world. It is because getting a health claim authorised in Great Britain is a process most ingredients never go through.
| 2,000+ yrs of recorded use in European herbal practice | 5–10 yrs typical time to take a claim through authorisation | £100K+ typical cost of a single claim dossier |
Authorisation is funded by whoever stands to profit from the claim, and no company will spend six figures on an ingredient any competitor can then sell. So botanicals like milk thistle sit outside the register regardless of the evidence behind them. The lawful position is that we sell you a specification and you make your own decisions — which is what the rest of this guide helps you do.
Check it for yourself on the Great Britain Nutrition and Health Claims Register — search it for milk thistle or silymarin and you will find nothing.
This is also why you should be wary of any milk thistle page that does tell you what it is for. Wording that edges toward a bodily organ or a named medical condition is where a food supplement stops being a food supplement and starts being an unlicensed medicine — and that is a line drawn by law, not by taste.
Our Numbers, Through The Same Six Questions
Run the sum on ours too
| 1. Extract ratio | 40:1, stated on the label |
| 2. Standardisation | 80% silymarin |
| 3. In milligrams | 80mg silymarin per tablet |
| 4. Part used | Seed |
| 5. Species | Silybum marianum |
| 6. Stated serving | Two to three tablets daily — so 160mg to 240mg of silymarin a day |
Vegan and vegetarian, non-GMO, free from all fourteen allergens named in UK law, made in the UK. And one thing we will say against ourselves: the document we hold is a manufacturer's specification sheet, not a batch Certificate of Analysis — it carries no heavy metal or microbiological results. We have asked for those on future batches and the figures will go on the product page when they arrive.
One Thing Almost No Milk Thistle Page Mentions
Milk thistle is in the daisy family. Silybum marianum belongs to the Asteraceae, alongside ragweed, chrysanthemum, marigold and daisy. If you react to any of those, speak to your doctor or pharmacist before taking milk thistle in any form.
Botanical extracts can also interact with prescription medicines, so a pharmacist is the right person to check your own list. Milk thistle supplements are for adults, and are not suitable during pregnancy or breastfeeding.
Questions
Is milk thistle a medicine?
No. Milk thistle is sold in the UK as a food supplement, not a licensed medicine, and no product may be presented as treating or preventing any condition.
Does milk thistle have any authorised UK health claims?
No. Neither milk thistle nor silymarin appears among the roughly 220 health claims authorised in Great Britain, so it can only lawfully be sold on specification.
Is a higher milligram figure better?
Not on its own. A "4000mg" ground-seed product can contain less silymarin than a 100mg standardised extract. Compare the silymarin figure, not the headline.
What does 40:1 mean?
Roughly forty parts of dried seed went into the extraction for each part of extract produced. It describes the process input, not the finished composition.
What is silymarin?
Silymarin is the group of compounds that milk thistle seed extracts are characterised and standardised by, including silibinin, silychristin and silydianin. It is the marker used to grade an extract.
Is 80% silymarin high?
It is at the top of the commercial range. Extracts are sold at 30%, 50%, 70% and 80%, and unextracted ground seed carries only a few percent.
Which part of the plant should it come from?
The seed. Silymarin is concentrated in the seed, so aerial-part or whole-herb material carries considerably less of it.
Can milk thistle be taken every day?
Follow the serving stated on the product you have bought and do not exceed it. If you take prescription medicine or have any medical condition, ask a pharmacist before starting it.
Who should avoid milk thistle?
It is for adults only and is not suitable during pregnancy or breastfeeding. Anyone who reacts to daisy-family plants such as ragweed, chrysanthemum or marigold should seek advice first, as should anyone on prescription medicine.
How can I check what is really in a product?
Ask the seller for the manufacturer's specification sheet or Certificate of Analysis. A seller who cannot produce one, or who will not state the silymarin percentage, has answered your question.
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How this guide is written
The extract and standardisation figures for our own product are taken from our manufacturer's specification sheet, not from marketing material. Claim wording is checked against the Great Britain Nutrition and Health Claims Register before publication, and where an ingredient has no authorised claim we say so rather than working around it. Where our documentation has a gap, it is stated. No competitor is named or compared, and no seller has paid for a mention. Written and maintained by Charge Products, trading since 2016.
This article is about extract ratios, standardisation and how to read a milk thistle label. It makes no claim about what milk thistle does in the body and none is intended — neither milk thistle nor silymarin carries an authorised health claim in Great Britain. The four products in the comparison table are illustrative examples constructed to show the arithmetic. They are not real products and are not intended to represent any particular seller.
Food supplements are not medicines. Not a substitute for a varied and balanced diet or a healthy lifestyle. Follow the serving stated on the product you buy and do not exceed it. Adults 18 and over only. Keep out of reach of children. Not suitable during pregnancy or breastfeeding. Milk thistle is a member of the Asteraceae (daisy) family — seek advice first if you react to related plants. Speak to your doctor or pharmacist before use if you take any prescription medicine or are under medical supervision.
Charge Products is a trading name of Big Idea Services Ltd, Company No. 11645389. Unit 1, 8 Towerfield Road, Southend-on-Sea, Essex SS3 9QE. 5 Star Food Hygiene Rating. Last updated: October 2026.
