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Western herbalism

Milk thistleSilybum marianum

A thistle fruit extract sold as silymarin. The Cochrane review of 18 liver-disease trials found no significant mortality effect; EMA lists a traditional digestive use.

Botanical name
Silybum marianum
Part used
ripe fruit (seed)
Also called
Holy thistle, Marian thistle, St. Mary's thistle, Silymarin (the extract)
Used in
Western herbalism
Taken for
Liver and bile, Indigestion
Sold as
capsules, tablets, tea, powder, tincture

The plant

Milk thistle is a tall thistle with large purple flowers, native to Europe and brought to North America by early colonists. The part used is the ripe fruit, commonly called the seed. Its main active material is silymarin, a mixture of compounds rather than a single molecule.

The herb is sold as the crushed seed for tea, as a powder, and more often as a standardized dry extract in capsules or tablets labeled by silymarin content. Extracts are made with solvents such as acetone, ethanol or ethyl acetate, which is why the EMA monograph lists nine different preparations with different amounts per dose.

NCCIH notes that milk thistle is sold mainly as a dietary supplement, and that some products contain silymarin in amounts that differ substantially from the label. The most researched use is liver disease; the digestive indication in European monographs is far less studied.

How the traditions use it

Western herbalism

Milk thistle has been used in European herbal practice for liver complaints, and NCCIH records historical use for liver disorders and to increase breast milk. In 2018 the European Medicines Agency adopted a traditional-use monograph for the fruit for the symptomatic relief of digestive disorders, a sensation of fullness and indigestion, and to support liver function, after serious conditions have been excluded by a doctor. EMA labels this an indication based only on long-standing use; the monograph is not a finding that the herb works.

What is in it

Silymarin is a mixture of flavonolignans, of which silybin is the most active in laboratory assays. In cell and animal work silymarin acts as an antioxidant and affects inflammatory signaling in liver cells, which is the basis for the liver research. These are laboratory and animal findings; whether they translate into a digestive effect in people is untested. A safety review reports that silymarin was mutagenic in Salmonella strains with metabolic enzymes present, while silybin, silydianin and silychristin were not cytotoxic or genotoxic at 100 micromolar.

What the human trials show

We could find no randomized trial of milk thistle on a digestive symptom such as fullness or indigestion, which is the indication EMA lists. The human evidence is in liver disease.

The Cochrane review of milk thistle for alcohol-related and hepatitis B or C liver disease included 18 randomized trials with 1,088 patients. Methodological quality was low, with only 28.6 percent of trials having high-quality features. Milk thistle versus placebo or no intervention had no significant effect on mortality (relative risk 0.78, 95% CI 0.53 to 1.15).

In fatty liver disease, a 2024 meta-analysis of 26 randomized trials with 2,375 patients found silymarin lowered liver enzymes (ALT and AST) and improved steatosis on liver histology (odds ratio 3.25), along with cholesterol and insulin measures. By contrast, a 48-week US phase II trial in 78 adults with non-alcoholic steatohepatitis tested 420 mg or 700 mg three times a day against placebo: 15 percent in the 700 mg group, 19 percent in the 420 mg group and 12 percent on placebo reached the primary histology endpoint (P = 0.79), meaning no benefit in the intention-to-treat analysis. NCCIH also says two NCCIH-funded studies, one in hepatitis C and one in non-alcoholic steatohepatitis, found no benefit from silymarin.

Overall NCCIH concludes that results in liver disease are conflicting or too limited to be conclusive. None of this addresses the digestive complaints in the monograph.

StudyDoseWhat it found
Cochrane review, 18 randomized trials, 1,088 patients with alcoholic or hepatitis B/C liver disease PMID 17943794VariousNo significant effect on mortality (RR 0.78, 95% CI 0.53 to 1.15); trial quality low
Phase II randomized trial, 78 adults with NASH PMID 31536511420 mg or 700 mg silymarin three times daily, 48 weeksHistology response 19% (420 mg), 15% (700 mg), 12% placebo; P = 0.79
Meta-analysis of 26 randomized trials in NAFLD/NASH, 2,375 patients PMID 38579127VariousLower ALT and AST; improved steatosis on histology (OR 3.25); better cholesterol and insulin measures

How much the studies and the texts used

The EMA traditional-use monograph lists, for adults: herbal tea of 3 to 5 g of comminuted fruit in 100 ml of boiling water, 2 to 3 times daily before meals; powder 300 to 600 mg, 2 to 3 times daily, up to 1,800 mg a day; and various dry extracts, for example 82 to 239 mg of an acetone extract (DER 20-70:1) 2 to 3 times daily, or 200 mg a day of an ethanol extract. Use in under-18s is not established. The monograph says to consult a practitioner after 2 weeks of symptoms. Trials in liver disease used far higher silymarin doses, up to 700 mg three times a day for 24 to 48 weeks.

Doses here describe what studies and pharmacopoeias used. They are not a recommendation for any person; a clinician or pharmacist who knows your medicines and conditions is the right person to ask.

Side effects and cautions

Milk thistle is generally well tolerated. NCCIH lists digestive effects as the commonest: bloating, nausea and gas. EMA lists mild gastrointestinal symptoms (dry mouth, nausea, upset stomach, gastric irritation, diarrhea), headache, and allergic reactions including dermatitis, urticaria, asthma and anaphylaxis, frequency unknown. Anyone hypersensitive to the Asteraceae (daisy) family, such as ragweed, chrysanthemum, marigold or daisy, is contraindicated.

A safety review found silymarin was safe at 700 mg three times a day for 24 weeks in trials, with nausea and diarrhea reported, and one trial suggested safety in pregnancy; EMA says pregnancy and breastfeeding data are insufficient and does not advise use. EMA advises consulting a doctor immediately if jaundice or a change in urine or stool color appears. NCCIH notes some products have been contaminated with pesticides, microorganisms or mycotoxins.

Interactions

EMA reports no interactions. A safety review concludes silymarin has low drug-interaction potential and no major effects on the cytochrome P-450 enzymes, while advising caution with narrow-therapeutic-window medicines. NCCIH gives only general advice to speak to a health care provider before combining herbs and medicines. No medicine class has a documented, clinically significant interaction in the sources we read.

Medicines the quiz checks milk thistle against

When a quiz taker names one of these medicines, the rule below fires. Each comes from a published interaction reference; none is a diagnosis:

Milk thistle on the shelf: the products that contain it

The products here name milk thistle among their actives. How much of it a serving holds, and whether that matches any trial, is on each page.

Inno Supps Inno Cleanse 4.1 out of 5 from 12,407 ratings from Amazon · $1.33 a day Omyo GLP-1 Digestive Support 4.8 out of 5 from 2,814 ratings from omyohealth.com · $2.00 a day JSHealth Vitamins Detox + Debloat Formula 4.3 out of 5 from 2,339 ratings from Amazon · $1.30 a day ActivatedYou Morning Complete 3.9 out of 5 from 1,503 ratings from Trustpilot · $2.08 a day Akka Liver and Gut Superbiotic 4.4 out of 5 from 1,107 ratings from Amazon · $2.13 a day Biocidin Botanicals Biocidin Broad-Spectrum Liquid Formula 4.5 out of 5 from 1,079 ratings from Amazon · ~$1.41 per day at the full 15-drop dose DelighTeas Ayurvedic Stomach Relief & Happy Liver Tea 4.6 out of 5 from 1,040 ratings from Amazon · $0.34 a day Greek Wellness Natural Colon 4.3 out of 5 from 46 ratings from Amazon · $0.83 a day

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Often paired or compared

Western Artichoke Cynara cardunculus (syn. Cynara scolymus) Western / TCM Dandelion Taraxacum officinale (and T. mongolicum in Chinese medicine) Ayurvedic / TCM / Western Turmeric Curcuma longa Western Gentian Gentiana lutea TCM Schisandra Schisandra chinensis (bei wu wei zi); Schisandra sphenanthera (nan wu wei zi)

Common questions

Is milk thistle the same as silymarin?

Silymarin is the mixture of compounds extracted from the fruit, and silybin is its main component. Most capsules are labeled by silymarin content. The crushed seed used for tea contains far less per serving.

Has it been tested for indigestion or bloating?

We could find no randomized trial for those symptoms. EMA lists digestive discomfort and fullness as a traditional use only. The trials we found were in liver disease.

What did the largest liver reviews show?

The Cochrane review of 18 trials in alcohol-related and viral liver disease found no significant effect on mortality. A 2024 meta-analysis in fatty liver disease found improvements in liver enzymes and steatosis, while a 48-week phase II trial in NASH found no histology benefit over placebo. NCCIH calls the evidence conflicting or too limited to be conclusive.

Who should not take it according to the monograph?

EMA contraindicates milk thistle in anyone hypersensitive to plants of the Asteraceae family. It does not advise use in pregnancy, breastfeeding or under age 18 because data are lacking. It says to see a doctor if jaundice appears.

Does the amount on the label match the product?

Not always. NCCIH reports that some supplements contain silymarin amounts that differ substantially from the label. Contamination with pesticides, microorganisms and mycotoxins has also been found in some products.

Sources