Milk thistle (Silybum marianum) is a prickly plant of the daisy family, and its seeds go into food supplements as ground seed or as a concentrated extract. The compounds that matter on a label are grouped under the name silymarin, and good extracts are standardised to 70 to 80 % of it. The EU has not authorised a health claim for milk thistle or silymarin, so a page that says milk thistle cleanses or protects the liver goes further than the law allows.
Below you will find what is in a capsule, how seed powder differs from a standardised extract, how much silymarin the milk thistle products in our range give, how to take them, who should stay away, and the one liver claim that does exist, for a different substance called choline.
What milk thistle is
Milk thistle grows across Europe and is known by several names: in English also Mary thistle, in Lithuanian margainis or tikrasis margainis, and in some texts "pieno usnis", which is a literal translation. The white veins on the leaves gave it the "milk" in the name. The part used in supplements is the seed, botanically a small fruit.
According to the US National Center for Complementary and Integrative Health (NCCIH), studies of milk thistle in people with liver conditions have given mixed results. None of that research became an authorised EU health claim. The European Medicines Agency has published a monograph on milk thistle fruit, but it concerns herbal medicines, and we do not use it to describe a food supplement.
Silymarin and standardisation
Silymarin is not one molecule but a mixture of flavonolignans found in the seed. A standardised extract is made so that every batch holds a stated share of silymarin, usually 70 to 80 %. That is what makes two bottles comparable. Ground seed is just the plant, and the silymarin content depends on the harvest, so a label usually gives the weight of seed and nothing about silymarin.
Read the line that says "silymarin" or "silymarin flavonoids" in milligrams per daily portion. A big number next to "milk thistle seed" or "extract" tells you the weight of the plant material, not how much silymarin it contains.
Forms: seed capsules, extract and blends
- Seed powder in capsules. Whole-plant material, simple and cheap per gram, but without a stated silymarin content.
- Standardised extract. A concentrate with a declared silymarin share. Our NOW Foods product also adds turmeric root, so part of every capsule is turmeric.
- Blends with dandelion and other roots. The milk thistle share is smaller, and the other herbs bring their own warnings.
- Liquid extracts. Sold elsewhere, some made with alcohol. We do not list one at the moment.
How much silymarin you get from our products
The table uses only what is printed on each label. Where a label does not state silymarin, we leave it blank instead of guessing.
| Product | Form | Label daily portion | Silymarin on the label | Pack lasts |
|---|---|---|---|---|
| NOW Foods silymarin 150 mg with turmeric, 60 capsules | Standardised extract plus turmeric | 2 capsules, 1 to 3 times a day (up to 6 capsules) | 240 mg silymarin flavonoids in 6 capsules (900 mg extract, 2100 mg turmeric) | 10 days at 6 capsules, 30 days at 2 |
| Swanson Full Spectrum milk thistle seed 500 mg, 30 or 100 capsules | Ground seed | 2 capsules, 2 to 3 times a day (4 to 6 capsules) | Not stated (2000 to 3000 mg of seed) | 100 capsules: 17 to 25 days |
| Swanson milk thistle, dandelion and yellow dock, 120 capsules | Seed blended with roots | 2 capsules a day | Not stated (700 mg of seed, 250 mg dandelion root, 250 mg yellow dock root, 100 mg beet root) | 60 days |
One thing the table makes visible: the NOW Foods figure belongs to the 6-capsule maximum. At the lowest label portion of 2 capsules you would get a third of it, which is 80 mg of silymarin flavonoids, so quote the portion together with the number.
Seed or extract
If you want to know what you are taking, choose the product that states silymarin, which in our range is the NOW Foods extract. If you prefer plain plant material and accept that the active content is not declared, seed capsules are the simpler option and cost less per day. A blend is for people who specifically want the other herbs, and those herbs change the list of cautions below.
All three products are in our milk thistle category, and you can see the wider group in supplements for the liver.
How to take milk thistle
There is no official recommended intake for silymarin, so the label is your guide. The NOW Foods label says 2 capsules once to three times a day with a meal. The Swanson seed capsules say 2 capsules two to three times a day with water, and the blend says 2 capsules a day with water. Do not exceed the stated daily portion, and count turmeric and other herbs from other supplements you take. Do not take two milk thistle products on the same day, because the amounts add up and the label of neither one knows about the other.
Split the daily portion across the day only as far as the label allows, and take it with the same meal each day so you do not skip it. Labels do not state how long to take it. If you plan to use it for months, ask a pharmacist.
Who should avoid milk thistle and what it can interact with
- Allergy to related plants. Milk thistle belongs to the daisy family (Asteraceae). NCCIH reports allergic reactions, mainly in people allergic to ragweed, marigold, daisy or chrysanthemum.
- Pregnancy and breastfeeding. Reliable safety data are lacking. The NOW Foods and Swanson blend labels say not for pregnant or breastfeeding women, and the Swanson seed label says to ask a doctor.
- Gallbladder and bile duct problems. The Swanson blend label names kidney stones, intestinal obstruction, bile duct obstruction and gallbladder problems. The NOW Foods label asks people with a gallbladder function disorder to consult a doctor, partly because of the turmeric.
- Medicines. Research on interactions with prescription drugs is limited and mixed. If you take regular medicines, ask a doctor or pharmacist before starting.
- Side effects. NCCIH describes them as uncommon and mild, such as stomach upset or loose stools.
If you have a liver disease, or a blood test showed raised liver enzymes, see a doctor. A food supplement is not a treatment, and it should not delay a diagnosis.
What EU law lets us say, and why choline is different
Regulation (EU) No 432/2012 lists the authorised health claims. There is none for milk thistle or silymarin, which is why our milk thistle product pages carry no health claims at all.
The liver appears in that list only for choline. These are the three authorised choline claims, and they may be used when a daily portion gives at least 82.5 mg of choline:
- Choline contributes to normal homocysteine metabolism
- Choline contributes to normal lipid metabolism
- Choline contributes to the maintenance of normal liver function
The Solgar choline capsule gives 350 mg of choline (as choline bitartrate) a day, so it meets the condition. Choline is a nutrient in its own right and has nothing to do with the milk thistle plant, so we do not present one as the reason for the other. EFSA's adequate intake for adults is 400 mg a day from all sources, and eggs, meat and soya are among the foods that contain it. The capsule suits people who want choline specifically, and women who are pregnant or breastfeeding, like people on medicines, should ask a doctor first.
How to choose
- Decide whether you want a declared silymarin amount (extract) or plain seed.
- Read the silymarin line in mg per daily portion, not the weight of plant material.
- Check the label against your own situation: allergies, pregnancy, gallbladder problems, medicines.
- If turmeric or dandelion is in the product, count it as part of your intake from other supplements.
- Compare the price per day at the label portion, not the price of the pack.
FAQ
What is milk thistle?
A plant of the daisy family, Silybum marianum. Its seeds are used in supplements, and silymarin is the group of compounds extracts are standardised to.
Is milk thistle the same as pieno usnis or Mary thistle?
Yes, these are different names for the same plant.
Does milk thistle protect the liver?
The EU has authorised no such claim, and according to NCCIH the results of studies in people are mixed. We therefore do not say it. The authorised liver claim applies to choline.
How much silymarin should I take?
There is no official recommended intake. Follow the label: the NOW Foods product gives 240 mg of silymarin flavonoids in its 6-capsule maximum.
When is the best time to take milk thistle?
The NOW Foods label says with a meal. Use the same time each day so you do not forget it.
Can I take milk thistle while pregnant?
Reliable data are missing, and our labels advise against it or tell you to ask a doctor. Ask your doctor.
How long can I take milk thistle?
The labels do not state a duration. If you plan to take it for months, ask a pharmacist, and stop and see a doctor if you notice an allergic reaction.
Can it be combined with medicines?
Interaction research is limited. Ask a pharmacist, especially if you take regular prescription drugs.
Sources
- NCCIH: Milk thistle
- EMA: Silybi mariani fructus (milk thistle fruit), herbal monograph
- Regulation (EU) No 432/2012, authorised health claims
- EFSA: Dietary reference values for choline (2016)
Content reviewed by Inese Kalniņa, dietitian.
