TUDCA vs Milk Thistle: How They Compare

Vitality Supplements · Ingredient Guide

TUDCA vs Milk Thistle

A clear, factual comparison of two commonly compared supplements — TUDCA and milk thistle. This guide looks only at what each one is, their composition, the forms they come in, typical serving sizes, where they are sourced and how they are tested. It makes no health claims for either.

Last updated July 2026 · Written by Vitality Supplements Editorial Team · ~2,100 words · 8 min read
Food supplement information — not medical advice
UK manufactured ISO/IEC 17025 batch tested Certificate of Analysis on request Factual, no health claims
Quick answer
Which should you choose?
TUDCA and milk thistle are two very different things. TUDCA (tauroursodeoxycholic acid) is a bile acid — a single, defined molecule. Milk thistle is a plant extract from Silybum marianum seeds, standardised to a group of compounds called silymarin. They are not interchangeable and are not the same category of ingredient. Which one you choose comes down to which ingredient you are specifically looking for: a defined bile-acid molecule (TUDCA) or a standardised botanical extract (milk thistle). This guide compares them factually on composition, form, serving size and testing — it makes no claims about what either does in the body.
Key takeaways
  • TUDCA is a bile acid — a single defined molecule (tauroursodeoxycholic acid).
  • Milk thistle is a plant extract standardised to silymarin, a group of flavonolignans.
  • They are different classes of ingredient, not two versions of the same thing.
  • TUDCA is usually dosed in the hundreds of milligrams; milk thistle is standardised by its silymarin percentage.
  • For both, a stated composition, HPLC testing and a Certificate of Analysis are what matter.
  • Both are sold as UK food supplements with no authorised health claims.
Side by side

How they differ

The simplest way to see the difference is a direct comparison. The table below sets TUDCA and milk thistle next to each other on the factual points that actually distinguish them — what each one is, its composition, the forms sold, typical serving sizes, sourcing and testing. It deliberately says nothing about effects.

A factual comparison only. Serving sizes reflect what is common on the market, not recommendations. Neither ingredient carries authorised health claims in the UK.
Attribute TUDCA Milk thistle
What it is A bile acid — a single, defined molecule A plant (botanical) extract from milk thistle seeds
Full name Tauroursodeoxycholic acid (the taurine conjugate of UDCA) Extract of Silybum marianum, standardised to silymarin
Composition One molecule; purity is stated as a percentage (e.g. 98%+) A mixture of flavonolignans (silybin A & B, silychristin, silydianin) collectively called silymarin
Category Conjugated bile acid Plant polyphenol / flavonolignan complex
Source Manufactured to a defined chemical specification (modern material is produced synthetically, not from animal bile) The seeds of the milk thistle plant, a Mediterranean thistle
Common forms Capsules or powder; sold by milligram amount of TUDCA Capsules or tablets; sold by extract weight and silymarin percentage
Typical serving on the market Commonly 250–1100mg of TUDCA per day Commonly 150–400mg of extract, often standardised to ~80% silymarin
Key label number mg of TUDCA and stated purity Extract mg and the silymarin standardisation %
Testing that counts HPLC purity and identity, with a Certificate of Analysis HPLC for silymarin content, with a Certificate of Analysis
One is a single bile-acid molecule; the other is a standardised plant extract. That is the core difference.
Ingredient one

What TUDCA is

TUDCA stands for tauroursodeoxycholic acid. Chemically it is a bile acid — specifically the taurine-conjugated form of ursodeoxycholic acid (UDCA). Bile acids are molecules the body naturally produces, and TUDCA occurs in only small amounts in humans. As a supplement it is a single, defined molecule, which means its label can state a precise milligram amount and a purity percentage.

On supplement labels TUDCA is usually sold by the milligram amount of TUDCA itself — for example 250mg, 500mg or 1100mg per serving — alongside a stated purity such as 98% or higher. Because it is one compound rather than a botanical blend, the meaningful checks are its identity and purity, confirmed by HPLC, and a batch CoA. Historically bile acids were obtained from animal sources; the material used in modern quality supplements is produced to a defined chemical specification.

A defined molecule
Single compound. TUDCA is one molecule, so labels can state an exact mg amount and purity percentage.
A bile acid
Its class. It is the taurine conjugate of UDCA, part of the bile-acid family the body produces naturally in small amounts.
Sold by mg
Label format. Typically 250–1100mg of TUDCA per serving, with a stated purity such as 98%+.
Purity is the check
What to verify. Identity and purity by HPLC, backed by a Certificate of Analysis for the batch.
Ingredient two

What milk thistle is

Milk thistle is a plant — Silybum marianum, a Mediterranean thistle. As a supplement it is a botanical extract made from the plant's seeds. Unlike TUDCA, it is not a single molecule: the active fraction is a group of related compounds called silymarin, which itself is made up of flavonolignans such as silybin (A and B), silychristin and silydianin.

Because it is an extract of a mixture, the number that matters most on a milk thistle label is the silymarin standardisation percentage. A common specification is an extract standardised to around 80% silymarin. So a 200mg extract standardised to 80% provides roughly 160mg of silymarin. As with any botanical, the meaningful checks are the stated standardisation, HPLC verification of silymarin content, and a Certificate of Analysis. An extract weight with no silymarin percentage tells you comparatively little.

With milk thistle, the silymarin percentage is the number that carries the information — not the raw extract weight.
Seeds
Plant partMilk thistle extract is made from the seeds of Silybum marianum.
~80%
Common standardisationThe typical stated silymarin percentage of the extract.
4+
Compounds in silymarinSilybin A & B, silychristin, silydianin and related flavonolignans.
HPLC
The test that countsConfirms the silymarin content behind the standardisation claim.
Making the choice

Which is right for you

Because TUDCA and milk thistle are different categories of ingredient, choosing between them is really about which specific ingredient you are looking for, rather than one being a stronger version of the other. They are often discussed together simply because both are popular standalone supplements — not because they are substitutes.

  • If you specifically want TUDCA, look for a stated mg of TUDCA, a purity figure (e.g. 98%+) and HPLC testing with a Certificate of Analysis.
  • If you specifically want milk thistle, look for the silymarin standardisation % (e.g. 80%), not just the raw extract weight.
  • Compare like with like — a milligram of a single-molecule bile acid is not equivalent to a milligram of a botanical extract.
  • For either, prefer UK manufacturing, clear labelling and independent, accredited testing.
  • Introduce one product at a time, and speak to a healthcare professional before starting any new supplement.

People researching these often look at them alongside other longevity supplements. For a deeper, single-ingredient explainer, see our what is TUDCA guide. Whatever you choose, the same principle applies to both: buy on verified composition, not on the biggest number on the label.

Common questions

TUDCA vs milk thistle FAQ

No. TUDCA is a bile acid — a single, defined molecule (tauroursodeoxycholic acid). Milk thistle is a plant extract from Silybum marianum seeds, standardised to a group of compounds called silymarin. They are different categories of ingredient, not two versions of the same supplement.
Silymarin is the name for the group of active compounds in milk thistle extract — a complex of flavonolignans including silybin A and B, silychristin and silydianin. Milk thistle extracts are usually standardised to a percentage of silymarin, commonly around 80%.
TUDCA stands for tauroursodeoxycholic acid. It is a bile acid — the taurine-conjugated form of ursodeoxycholic acid (UDCA). Because it is a single molecule, its label can state a precise milligram amount and a purity percentage.
On the market, TUDCA is commonly sold at 250–1100mg of TUDCA per day, with a stated purity. Milk thistle is sold by extract weight (commonly 150–400mg) together with a silymarin standardisation percentage. These figures reflect what products offer rather than recommended doses — there is no official RDA for either, so speak to a healthcare professional before starting.
Some people take both as separate supplements. Because they are different ingredients, that is a personal choice rather than a necessity, and neither replaces the other. As with combining any supplements, introduce one product at a time and check with a healthcare professional, particularly if you take medication or manage a health condition.
For TUDCA: the mg of TUDCA, a purity figure (e.g. 98%+), HPLC testing and a Certificate of Analysis. For milk thistle: the extract weight and the silymarin standardisation percentage (e.g. 80%), again with HPLC verification and a CoA. In both cases, independent accredited testing and clear UK labelling matter most.

Looking for TUDCA?

Our Premium TUDCA is 1100mg per serving, UK-manufactured and independently batch tested, with a Certificate of Analysis available on request.

Shop TUDCA 1100mg → Read: What is TUDCA?
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About the author. This guide was written and reviewed by the Vitality Supplements Editorial Team, a UK supplement manufacturer. Every batch we produce is independently tested by an ISO/IEC 17025-accredited laboratory, with a Certificate of Analysis available on request.

This article is for general information about food supplements and is not medical advice. TUDCA and milk thistle are sold as food supplements in the UK and carry no authorised health claims. This comparison describes what each ingredient is and how it is composed and tested; it does not claim either has any effect on health or the body. Always consult a qualified healthcare professional before starting any supplement, particularly if you are under 18, pregnant, breastfeeding, taking medication or managing a health condition. References available on our research references page.