Milk thistle

What it is

Milk thistle is a flowering plant whose seed extract is sold for liver complaints. NCCIH describes it as "a tall plant with large purple flowers that is native to Europe" and notes that "The main constituent of milk thistle extract is silymarin, a mixture of compounds." LiverTox records that it "is marketed as capsules or tablets containing ethanol extracted silymarin in amounts of 250 to 750 mg", and that "Intravenous preparations of purified silybinin are approved in Europe for therapy of Amanita phalloides mushroom poisoning" — a different, injected product from the capsules sold as supplements.

What the research says

Milk thistle is the archetypal liver supplement, and the liver evidence is the weakest part of its file. The Cochrane review of 13 randomised trials in 915 patients with alcohol-related or viral liver disease found no significant effect on mortality, complications or liver histology. NCCIH reports that a trial it funded in hepatitis C did not show a benefit from silymarin. A 78-patient randomised trial in non-alcoholic steatohepatitis missed its histological endpoint. The clearest positive signal is somewhere else entirely — small trials of blood sugar in type 2 diabetes — and even that meta-analysis calls its own evidence insufficient. Safety is genuinely reassuring: LiverTox rates milk thistle unlikely to cause liver injury, and Cochrane found no increase in adverse events. The real-world risks are allergy and product quality rather than toxicity.

Evidence grade: Not supported by the research.

What goes wrong

NCCIH reports that some milk thistle products have contained silymarin amounts different from their labels, or contaminants. (Source 1)

• Official position, Certainty not rated.
• Size: not quantified.
• Who: milk thistle dietary supplements sold in the United States and other countries.
• How long: not applicable.
• Result: no numbers given; a qualitative product-quality warning.
• Funding: US government agency (NCCIH)

Some products have been found to contain amounts of silymarin substantially different from what's stated on the label or to be contaminated with pesticides, microorganisms, or mycotoxins (harmful substances produced by molds or other fungi).

NCCIH warns of allergic reactions, particularly in people allergic to related Asteraceae plants. (Source 1)

• Official position, Certainty not rated.
• Size: not quantified.
• Who: people allergic to ragweed, chrysanthemum, marigold and daisy.
• How long: not applicable.
• Result: no incidence figures given; most common side effects described as digestive symptoms such as bloating, nausea and gas.
• Funding: US government agency (NCCIH)

Milk thistle may cause allergic reactions, particularly among people who are allergic to related plants (for example, ragweed, chrysanthemum, marigold, and daisy).

A published case report documents respiratory allergy confirmed on skin testing to milk thistle. (Source 2)

• Case report, Very low certainty.
• Size: 1 patient.
• Who: a 29-year-old man occupationally exposed to milk thistle and teff.
• How long: single episode, investigated at an allergy clinic.
• Result: skin test with native allergens: milk thistle 16/35, teff flour 22/60, negative control 0/0, histamine 3/5.
• Funding: not stated.

He also reported sneezing, runny nose, watering and burning eyes, and wheezing following inhalation exposure to ground milk thistle.

What the evidence supports

NCCIH also reports a positive but geographically narrow signal for blood sugar control in type 2 diabetes. (Source 3)

• Official position, Certainty not rated.
• Size: a small number of studies in people.
• Who: people with type 2 diabetes, mostly studied in Middle Eastern countries.
• How long: not applicable.
• Result: no numbers given.
• Funding: US government agency (NCCIH)

Results from a small number of studies in people show that milk thistle extracts may help to control blood sugar in people with type 2 diabetes.

Cochrane found no increase in adverse events with milk thistle compared with placebo. (Source 4)

• Systematic review, Low certainty.
• Size: 13 trials, 915 patients.
• Who: patients with alcohol-related or hepatitis B/C liver disease.
• How long: varied.
• Result: adverse events RR 0.83, 95% CI 0.46 to 1.50.
• Funding: Cochrane Hepato-Biliary Group review.

Milk thistle was not associated with a significantly increased risk of adverse events (RR 0.83, 95% CI 0.46 to 1.50).

LiverTox rates milk thistle as an unlikely cause of clinically apparent liver injury and finds little evidence of clinically significant herb-drug interactions. (Source 5)

• Official position, Moderate certainty.
• Size: not applicable.
• Who: people with and without liver disease taking milk thistle.
• How long: not applicable.
• Result: likelihood score E (unlikely cause of clinically apparent liver injury)
• Funding: US National Institute of Diabetes and Digestive and Kidney Diseases (LiverTox)

Despite its wide spread use in patients with and without liver disease, milk thistle has not been implicated in causing serum enzyme elevations or clinically apparent acute liver injury.

The NASH trial reported no significant difference in adverse events between silymarin and placebo. (Source 6)

• Randomized trial, Moderate certainty.
• Size: 78 randomised participants.
• Who: non-cirrhotic adults with NASH.
• How long: 48 weeks.
• Result: no significant differences in adverse events among the treatment groups.
• Funding: trial of a proprietary product (Legalon®, Rottapharm|Madaus, Mylan)

There were no significant differences in adverse events among the treatment groups.

What the evidence does not support

The Cochrane review found milk thistle had no significant effect on mortality, complications of liver disease or liver histology in alcohol-related or viral liver disease. (Source 4)

• Systematic review, Low certainty.
• Size: 915 patients across 13 randomised clinical trials.
• Who: patients with alcoholic and/or hepatitis B or C virus liver diseases.
• How long: varied by trial.
• Result: mortality RR 0.78, 95% CI 0.53 to 1.15; complications RR 0.95, 95% CI 0.83 to 1.09; liver-related mortality RR 0.50, 95% CI 0.29 to 0.88 in all trials but RR 0.57, 95% CI 0.28 to 1.19 in high-quality trials only.
• Funding: Cochrane Hepato-Biliary Group review; funding not stated in abstract.

Milk thistle versus placebo or no intervention had no significant effect on mortality (RR 0.78, 95% CI 0.53 to 1.15), complications of liver disease (RR 0.95, 95% CI 0.83 to 1.09), or liver histology.

Cochrane's stated conclusion is that milk thistle's benefits in liver disease are in question and the supporting evidence is not of high quality. (Source 7)

• Systematic review, Low certainty.
• Size: 13 trials, 915 patients.
• Who: patients with alcoholic and/or hepatitis B or C virus liver diseases.
• How long: varied.
• Result: narrative conclusion; no additional pooled estimate.
• Funding: Cochrane Hepato-Biliary Group review.

Our results question the beneficial effects of milk thistle for patients with alcoholic and/or hepatitis B or C virus liver diseases and highlight the lack of high‐quality evidence to support this intervention.

A randomised trial of silymarin in non-alcoholic steatohepatitis found no benefit on its histological primary endpoint. (Source 6)

• Randomized trial, Moderate certainty.
• Size: 78 randomised of 116 screened.
• Who: non-cirrhotic adults with biopsy-confirmed NASH (NAFLD Activity Score ≥4) at 5 US medical centres.
• How long: 48 weeks.
• Result: primary endpoint reached by 4/27 (15%) on 700 mg, 5/26 (19%) on 420 mg and 3/25 (12%) on placebo (p = 0.79); 49 (63%) of participants did not meet histological entry criteria on central review; fibrosis stage improved most in the placebo group.
• Funding: trial tested a proprietary product (Legalon®, Rottapharm|Madaus, Mylan); registered as NCT00680407.

After 48–50 weeks, 4/27 (15%) in the 700 mg dose, 5/26 (19%) participants randomized to 420 mg, and 3/25 (12%) of placebo recipients reached the primary endpoint (p = 0.79) among all randomized participants, indicating no benefit from silymarin in the intention to treat analysis

The same meta-analysis says the available evidence is not sufficient to conclude. (Source 8)

• Meta-analysis, Very low certainty.
• Size: 7 trials, 350 patients.
• Who: patients with type 2 diabetes.
• How long: not stated.
• Result: results for lipid outcomes described as imprecise and uncertain.
• Funding: not stated.

overall the available evidence is insufficient to make a firm conclusion

Where the evidence is mixed

The Cochrane authors judged the underlying trials to be methodologically poor, with only about a quarter reporting adequate allocation concealment. (Source 4)

• Systematic review, Low certainty.
• Size: 13 trials, 915 patients.
• Who: patients with alcohol-related or hepatitis B/C liver disease.
• How long: varied.
• Result: 23% of trials reported adequate allocation concealment; 46% were considered adequately double-blinded.
• Funding: Cochrane Hepato-Biliary Group review.

The methodological quality was low: only 23% of the trials reported adequate allocation concealment and only 46% were considered adequately double‐blinded.

A meta-analysis of seven small trials found silymarin lowered fasting blood sugar and HbA1c in type 2 diabetes, while calling its own evidence insufficient for a firm conclusion. (Source 8)

• Meta-analysis, Low certainty.
• Size: 350 patients across 7 clinical trials.
• Who: patients with type 2 diabetes mellitus.
• How long: databases searched to 28 November 2020; trial durations not stated in the abstract.
• Result: the abstract reports direction only, with no pooled effect sizes or confidence intervals given: decreases in FBS, HbA1C and LDL-C, no effect on total cholesterol or triglycerides.
• Funding: not stated.

The results show that silymarin supplementation can decrease fasting blood sugar (FBS), hemoglobin A1C (HbA1C), and low density lipoprotein cholesterol (LDL-C), but it has no effect on total cholesterol (TC) or total triglyceride (TG).

What official bodies say

NCCIH states that two NIH-funded trials of silymarin, in hepatitis C and in fatty liver disease, showed no benefit. (Source 3)

• Official position, Certainty not rated.
• Size: two NCCIH-funded trials plus a wider trial literature.
• Who: people with alcohol-related liver disease, hepatitis B and C, NAFLD, and chemotherapy- or toxin-related liver problems.
• How long: not applicable.
• Result: no numbers given; a narrative position.
• Funding: US government agency (NCCIH)

Two studies funded by the National Center for Complementary and Integrative Health—one on hepatitis C and one on non-alcoholic steatohepatitis (a progressive form of fatty liver disease)—did not show benefits from supplementation with the milk thistle extract silymarin.

Where the research disagrees

Whether silymarin has any clinical benefit worth taking it for

• Cochrane Hepato-Biliary Group (Rambaldi and colleagues), systematic review and meta-analysis of 13 randomised trials, 915 patients: "Our results question the beneficial effects of milk thistle for patients with alcoholic and/or hepatitis B or C virus liver diseases and highlight the lack of high‐quality evidence to support this intervention." (Source 7)
• Authors of the 2021 silymarin type 2 diabetes meta-analysis, meta-analysis of 7 clinical trials, 350 patients: "The results show that silymarin supplementation can decrease fasting blood sugar (FBS), hemoglobin A1C (HbA1C), and low density lipoprotein cholesterol (LDL-C)" (Source 8)

Whether intravenous silibinin for mushroom poisoning tells you anything about oral capsules

• LiverTox (NIDDK), narrative review of an approved intravenous drug, not the oral supplement: "Intravenous preparations of purified silybinin are approved in Europe for therapy of Amanita phalloides mushroom poisoning." (Source 9)
• NCCIH, government position statement on the oral supplement literature: "There isn't enough high-quality evidence to allow definite conclusions to be reached about the effects of milk thistle on health conditions in people." (Source 10)

How much

• Reference intake: No reference intake (RDA or AI) exists for milk thistle or silymarin — they are not essential nutrients. NCCIH describes it only as a plant promoted as a supplement: "Milk thistle is promoted as a dietary supplement for liver disorders, diabetes, and other conditions." (Source 11)
• Upper limit: No tolerable upper intake level or acceptable daily intake has been set for silymarin by EFSA, the US Institute of Medicine or NIH. LiverTox instead records the marketed range: milk thistle "is marketed as capsules or tablets containing ethanol extracted silymarin in amounts of 250 to 750 mg and is purported to be beneficial for liver disease". (Source 9)
• Studied: Legalon® 420 mg or 700 mg three times daily for 48 weeks in non-alcoholic steatohepatitis (Source 12)
• Studied: Typical marketed capsules or tablets contain 250 to 750 mg of ethanol-extracted silymarin, taken 2 to 3 times daily (Source 9)

A common belief, and what the research shows

The belief: Milk thistle protects or repairs the liver, so it is worth taking if you drink, have hepatitis, or have a fatty liver.

What the research shows: The randomised evidence in exactly those conditions is null. Cochrane, pooling 13 trials in 915 patients, found that "Milk thistle versus placebo or no intervention had no significant effect on mortality (RR 0.78, 95% CI 0.53 to 1.15), complications of liver disease (RR 0.95, 95% CI 0.83 to 1.09), or liver histology." A 78-patient NASH trial reported no benefit, with placebo doing best on fibrosis. NCCIH summarises that two trials it funded "did not show benefits from supplementation with the milk thistle extract silymarin." The intravenous silibinin used in Europe for Amanita mushroom poisoning is a different product given a different way, and does not transfer to oral capsules.

Questions and answers

What is it?

Silymarin is a mix of polyphenol compounds called flavonolignans, extracted from the seeds of the milk thistle plant, Silybum marianum. Its main parts are silybin (also called silibinin), silychristin, silydianin and isosilybin; silybin makes up about 30%. (Source 13)

What does it do in the body?

Silymarin is widely believed to protect the liver through anti-inflammatory and antioxidant effects. In people, the measured effect is on liver enzyme blood tests: a 2025 meta-analysis of 55 randomised trials (3,545 patients) found lower AST and ALT, but no significant change in ALP. That meta-analysis measured only enzyme levels, so it does not show whether people's health or liver outcomes improved. (Source 14)

Is it good or bad for you?

Silymarin looks safe in trials, but its benefit is unproven. A 2025 Cochrane review in fatty liver disease (MASLD) found that silymarin on its own (monotherapy, not silymarin complex) may lower liver enzymes compared with no treatment or placebo, and that neither form lowered enzymes compared with other treatments. The evidence was low to very low certainty and there was not enough data on outcomes that matter to patients. A separate meta-analysis found no significant enzyme effect in drug-induced or alcohol-related liver injury, or in people with a BMI of 30 or more (Hasanpour 2025). Stomach upset occurred at placebo rates, and allergic reactions are rare (Rainone 2005). (Source 15)

How do you get more of it?

Silymarin comes from milk thistle seeds and is mainly taken as an extract in capsules or tablets. The body absorbs very little of it: in humans, the absolute oral bioavailability of silybin was measured at about 0.45%, because it dissolves poorly, crosses the gut wall poorly and is quickly processed by the liver and cleared in bile. Because of that, researchers have tested special formulations such as phytosomes and liposomes to improve absorption (Theodosiou 2014). (Source 13)

If it is harmful, what reduces it?

Does not apply in the usual sense. The body processes silybin quickly and clears it into bile and urine. The main documented risk is allergy: people allergic to plants in the aster (daisy) family are warned against it (Rainone 2005). (Source 16)

Why might someone be low in it or missing it?

Does not apply. Silymarin is a plant compound from milk thistle seeds, not a vitamin, mineral or other nutrient the body needs. The reviews we read describe no deficiency state, so being 'low' in it is not a recognised condition. (Source 13)

Which whole foods contain it or feed it?

Milk thistle itself is a wild edible plant in Mediterranean diets. People eat its stems, flower heads, leaf mid-ribs, sprouts and seeds, and in Spain it has been eaten as a salad vegetable or cooked. The fruits (seeds) are the parts used to make silymarin, and seeds had the highest phenolic content. No common everyday food supplies meaningful amounts. (Source 17)

What happens if you do not have it?

Nothing is known to happen, because silymarin is not an essential nutrient. Even as a treatment, a 2025 Cochrane review could not say whether taking it improves outcomes in fatty liver disease, because trials lacked data on outcomes such as death and quality of life. (Source 15)

How can you test for it?

We found no clinical test for silymarin 'levels' in a person. Blood silybin is measured only in research on how the body absorbs and processes it, and is very low after an oral dose. (Source 13)

We searched: Web searches for silymarin/silybin pharmacokinetics, bioavailability and clinical measurement reviews; read Li et al. 2025 (Pharmaceutics) and Theodosiou et al. 2014 (Phytochemistry Reviews). Neither describes a clinical or consumer test.

References

1. National Center for Complementary and Integrative Health (NIH). Milk Thistle. 2025. Read the source
2. Allergy, Asthma & Clinical Immunology. A case of allergy to Silybum marianum (milk thistle) and Eragrostis tef (teff). 2020. PMID 32322285, DOI 10.1186/s13223-020-00421-5. Read the source
3. National Center for Complementary and Integrative Health (NIH). Milk Thistle. 2025. Read the source
4. Cochrane Database of Systematic Reviews. Milk thistle for alcoholic and/or hepatitis B or C virus liver diseases. 2005. DOI 10.1002/14651858.CD003620.pub2. Read the source
5. National Institute of Diabetes and Digestive and Kidney Diseases (NIH), NCBI Bookshelf. Milk Thistle — LiverTox: Clinical and Research Information on Drug-Induced Liver Injury. 2020. Read the source
6. PLOS ONE. Silymarin in non-cirrhotics with non-alcoholic steatohepatitis: A randomized, double-blind, placebo controlled trial. 2019. PMID 31536511, DOI 10.1371/journal.pone.0221683. Read the source
7. Cochrane Database of Systematic Reviews. Milk thistle for alcoholic and/or hepatitis B or C virus liver diseases. 2005. DOI 10.1002/14651858.CD003620.pub2. Read the source
8. Obesity Medicine. The effects of silymarin on type 2 diabetes mellitus: A systematic review and meta-analysis. 2021. DOI 10.1016/j.obmed.2021.100368. Read the source
9. National Institute of Diabetes and Digestive and Kidney Diseases (NIH), NCBI Bookshelf. Milk Thistle — LiverTox: Clinical and Research Information on Drug-Induced Liver Injury. 2020. Read the source
10. National Center for Complementary and Integrative Health (NIH). Milk Thistle. 2025. Read the source
11. National Center for Complementary and Integrative Health (NIH). Milk Thistle. 2025. Read the source
12. PLOS ONE. Silymarin in non-cirrhotics with non-alcoholic steatohepatitis: A randomized, double-blind, placebo controlled trial. 2019. PMID 31536511, DOI 10.1371/journal.pone.0221683. Read the source
13. Pharmaceutics. Silymarin and Silybin: Rejuvenating Traditional Remedies with Modern Delivery Strategies. 2025. DOI 10.3390/pharmaceutics17121628. Read the source
14. BMC Complementary Medicine and Therapies. Are alterations needed in Silybum marianum (Silymarin) administration practices? A novel outlook and meta-analysis on randomized trials targeting liver injury. 2025. DOI 10.1186/s12906-025-04886-y. Read the source
15. Cochrane Database of Systematic Reviews. Silymarin for adults with metabolic dysfunction-associated steatotic liver disease (Cochrane review, plain language summary). 2025. PMID 40552569, DOI 10.1002/14651858.CD015524.pub2. Read the source
16. Phytochemistry Reviews. Bioavailability of silymarin flavonolignans: drug formulations and biotransformation. 2014. DOI 10.1007/s11101-013-9285-5. Read the source
17. Plants. Tunisian Silybum Species: Important Sources of Polyphenols, Organic Acids, Minerals, and Proteins across Various Plant Organs. 2024. PMID 38611518, DOI 10.3390/plants13070989. Read the source