Supplement

Milk thistle (silymarin)

Herbs · Silybum marianum, milk thistle, silymarin, silibinin

Milk thistle is Europe’s classic liver plant and has been sold in Germany for decades as a medicine for the supportive treatment of liver diseases. In meta-analyses, liver enzymes fall in fatty liver disease, and one trial found signs of less scarring. The methodologically best trials, however, missed their primary goal, and there is no effect on mortality.

What milk thistle is

Milk thistle, Silybum marianum, is a plant of the daisy family native to Europe. Its fruits are used. Their mixture of active compounds is called silymarin and consists of several flavonolignans; the most important component is silibinin. Milk thistle is sold as a tea, as a standardized dry extract in medicines and as a food supplement.

In the BK-Score, human evidence stands at 6 out of 10. It goes no higher, and that is not due to a lack of studies but to their quality: there are many, but they are small and inconsistent. Related topics are TUDCA, NAC and berberine; the page Fatty liver gives an overview.

How it works

In cell and animal models, silymarin acts as an antioxidant, anti-inflammatory and antifibrotic agent; it stimulates protein synthesis in liver cells and stabilizes cell membranes. In human hepatic stellate cells, which are involved in scarring, silibinin inhibited their activation in a dose-dependent manner.

In humans, the mode of action has not been clarified. The assessment report of the EU herbal committee HMPC cites a review according to which the mechanism is not fully defined despite extensive laboratory and animal research and probably involves several pathways.

What is well supported

Long experience as a medicine. In Germany, milk thistle dry extracts have been sold since at least 1976 as medicines for the supportive treatment of chronic inflammatory liver diseases, liver cirrhosis and toxic liver damage. The HMPC counts more than 4,000 patients in clinical trials, mostly randomized and placebo-controlled.
Liver enzymes in fatty liver disease. A meta-analysis of 26 randomized trials with 2,375 patients found lower liver enzymes (ALT, AST), better blood lipids and more often less fat accumulation in the tissue sample. A second analysis of eight placebo-controlled trials confirmed the falling transaminases, independent of weight loss.
Signs of less scarring. In a double-blind trial in fatty liver inflammation, fibrosis regressed considerably more often under silymarin than under placebo, measured by biopsy and by liver stiffness.
Well tolerated. The HMPC found no statistically significant differences in serious adverse effects in the trials; observational studies cover more than 6,000 patients.

What the studies show

Li 2024 and Kalopitas 2021: fatty liver disease

In 2024, Li and colleagues analyzed 26 randomized trials with 2,375 NAFLD patients in the Annals of Hepatology. Silymarin lowered ALT and AST, total cholesterol, triglycerides and LDL, raised HDL and improved fatty liver indices; in the tissue sample, less fat accumulation was more frequent (OR 3.25; 1.80 to 5.87). The authors themselves write that the effects need further confirmation; the search also included a Chinese database. Kalopitas 2021, with eight placebo-controlled trials, arrived at falling transaminases independent of weight and points out quality shortcomings.

Wah Kheong 2017: fatty liver inflammation with biopsy

In Kuala Lumpur, 99 patients with confirmed NASH received 700 mg of silymarin three times daily or placebo for 48 weeks, after which a repeat biopsy was performed. The primary goal, an improvement in the NAFLD activity score of at least 30 percent, was reached by 32.7 versus 26.0 percent, not a significant difference. Fibrosis, by contrast, regressed in 22.4 versus 6.0 percent, and liver stiffness fell by at least 30 percent in 24.2 versus 2.3 percent. The authors see a possible antifibrotic effect that a larger trial needs to confirm.

Fried 2012: hepatitis C

In the US trial published in JAMA, 154 patients with chronic hepatitis C in whom interferon therapy had failed received 420 or 700 mg of silymarin three times daily or placebo for 24 weeks, that is, more than usual. The primary goal, normalized or halved liver enzymes, was reached by only two participants in each group. Viral load and quality of life did not differ either. Adverse effects were similar to those under placebo.

Rambaldi 2007: the Cochrane review

The Cochrane review covered 18 randomized trials with 1,088 patients with alcohol-related or viral liver diseases. There was no significant effect on all-cause mortality (RR 0.78; 0.53 to 1.15), on complications or on liver tissue. Liver-related mortality was halved across all trials (RR 0.50), but in the methodologically sound trials it was no longer significant (RR 0.57; 0.28 to 1.19). Only 28.6 percent of the trials showed features of high quality.

Voroneanu 2016: type 2 diabetes

Five randomized trials with 270 patients showed a reduction in fasting glucose of 26.9 mg/dl and in HbA1c of 1.07 percentage points, without an effect on blood lipids. Because of low quality and high heterogeneity, the authors make no recommendation; according to the NCCIH, much of this research comes from the Middle East.

Where the data stop

Living longer with liver disease. Neither all-cause mortality nor complications fell in the Cochrane review; the advantage in liver-related mortality disappeared in the sound trials.
Clinical endpoints instead of laboratory values. The positive meta-analyses mainly measure liver enzymes and fatty liver indices, that is, surrogate markers. The two methodologically strongest individual trials missed their primary endpoint; according to the NCCIH, two trials on hepatitis C and NASH funded by the US institute also showed no benefit.
“Liver detox” in healthy people. Studies in people without liver disease that show a detoxifying or protective effect were not found in the research. The HMPC recognizes only a traditional use to support liver function, explicitly after serious conditions have been ruled out by a doctor.
Viral hepatitis. According to the HMPC, there is no evidence of a favorable influence on the course of viral hepatitis.
Comparability. The trials used very different extracts, doses and durations. Results initially apply only to the preparation tested in each case.

Status, approval and legal

In Germany, milk thistle dry extracts are approved as medicines, according to the HMPC assessment report in the indications supportive treatment of chronic inflammatory liver diseases, liver cirrhosis and toxic liver damage, the oldest since at least 1976. The relevant dose is stated in the respective package leaflet.

At European level, the HMPC recognized only a traditional use in its 2018 monograph: for the relief of digestive complaints such as a feeling of fullness and to support liver function, after serious conditions have been ruled out by a doctor, for adults only. The committee rejected a well-established use because the trial data were not consistent enough. In hospitals, intravenous silibinin is used as an adjunct in poisoning with the death cap mushroom; this is a controlled medical treatment. Milk thistle is also sold as a tea and as a food supplement.

Safety

In the trials, milk thistle is considered well tolerated. The most common complaints are gastrointestinal, mostly mild: a mild laxative effect, abdominal pain, nausea, bloating, indigestion. In a meta-analysis on fatty liver disease, however, adverse effects occurred almost twice as often under silymarin as in the comparison groups (RR 1.98), mostly in the gastrointestinal tract. Headaches and allergic skin reactions up to severe allergic reactions have also been described; their frequency is not known. In people allergic to plants of the daisy family, milk thistle should not be used.

For pregnancy, breastfeeding and people under 18, data are lacking, and the HMPC advises against use there. The committee rates the data on the genotoxicity of the preparations as incomplete, without any sign of a carcinogenic effect in long-term animal experiments. The US institute NCCIH points out variable product quality: some preparations deviated considerably from the stated silymarin content or were contaminated with pesticides, microbes or mycotoxins. Elevated liver enzymes call for medical evaluation. In the BK-Score, safety data stands at 7 out of 10: well studied, not harmless. This text is information and does not replace medical advice.

BK-Score Supported, with caveats

Human evidence		6
Mechanism		4
Safety data		7
Hype gap		4
Track record of use		9

Evidence 6, because more than 4,000 patients have been studied in randomized trials (EMA/HMPC 2018) and meta-analyses in fatty liver disease show lower liver enzymes and less fat accumulation (Li 2024: 26 trials, 2,375 patients; Kalopitas 2021). Not higher, because the quality of the trials is consistently low, the Cochrane review found no effect on mortality (Rambaldi 2007: RR 0.78, not significant) and the methodologically best individual trials missed their primary goal (Fried 2012 in hepatitis C, Wah Kheong 2017 in NASH). Mechanism 4, because antioxidant, anti-inflammatory and antifibrotic effects have been shown mainly in cell and animal models and, according to the HMPC assessment, the mode of action is not fully clarified. Safety 7, because controlled trials and observational studies in more than 6,000 patients show only rare, mostly mild adverse effects, but according to the HMPC the data on genotoxicity are incomplete and data on pregnancy are lacking. Hype 4, because milk thistle is widely promoted for liver detox and liver protection, but the EU assessment recognizes only a traditional use. Use 9, because the plant has been used for centuries and extracts have been sold as medicines in Germany since at least 1976. Direction mixed: liver enzymes improve, clinical endpoints do not.

The score rates the state of knowledge, not the substance. “Safety data 7” means well studied – not harmless. “Track record of use 9” means used long and widely – that is not proof of efficacy.
Subjective assessment by Biohacking Kompakt based on published scoring rules – not a scientific rating and not a medical recommendation. Rules and all ratings (German)

Frequently asked questions about milk thistle

Does milk thistle help the liver?

In fatty liver disease, silymarin lowers liver enzymes in meta-analyses, and one trial found signs of less scarring. The Cochrane review on alcohol-related and viral liver diseases, however, found no effect on mortality, complications or liver tissue. The methodologically best individual trials missed their primary goal. Elevated liver enzymes therefore call for medical evaluation.

Does milk thistle help with fatty liver disease?

A meta-analysis of 26 randomized trials with 2,375 patients found lower liver enzymes and more often less fat accumulation in the tissue sample. In a 48-week double-blind trial with 99 NASH patients, the primary goal was missed, but fibrosis regressed more often than under placebo. The quality of the trials is low overall, and larger confirmation is lacking.

Does milk thistle detoxify the liver?

There are no studies on detoxification in healthy people. The EU herbal committee recognizes milk thistle only traditionally to support liver function and for digestive complaints, and only after serious conditions have been ruled out by a doctor. Intravenous silibinin is used in hospitals in death cap mushroom poisoning; that is something different from a tea or a capsule.

Is milk thistle a medicine?

In Germany, milk thistle dry extracts have been approved for decades as medicines for the supportive treatment of chronic inflammatory liver diseases, liver cirrhosis and toxic liver damage. There are also teas and food supplements. At EU level, the HMPC recognized only a traditional use in 2018.

What side effects does milk thistle have?

The most common are mild gastrointestinal complaints such as a mild laxative effect, nausea and bloating. Allergic reactions are possible, especially in people allergic to plants of the daisy family. The HMPC advises against use in pregnancy and breastfeeding and under 18 years of age because data are lacking. This information does not replace medical advice.

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Sources

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Information only, not medical advice and not a usage or dosage recommendation. Prescription-only and unapproved substances belong in the hands of a physician. Last updated: 2026-11-06.