Silybum marianum · herb
Evidence tier: weak
Protects and regenerates liver cells; supports skin clarity and detoxification
Silymarin, a mixture of flavonolignans from the seed, is thought to protect liver cells by scavenging free radicals, stabilising the hepatocyte membrane against toxin entry, and damping the inflammatory and fibrotic signalling that follows liver injury. This is the laboratory story and it is a good one. NCCIH's position is that researchers still do not fully understand why those effects appear in the lab, and that they did not translate into benefit in clinical trials. Treat the mechanism as plausible, not as demonstrated in people.
The most famous liver herb in the world, and the liver claim is the one that fails. Start with the highest tier of evidence: the Cochrane Hepato Biliary Group review of milk thistle for alcoholic and hepatitis B or C liver disease pooled 13 randomised trials in 915 patients and could not demonstrate significant effects on mortality or on complications of liver disease, in all trials combined or in the high quality trials (PMID 17943794). The pattern inside that review is the tell: liver related mortality looked reduced when every trial was thrown in (RR 0.50), and the effect disappeared once the analysis was restricted to the trials that were actually well conducted (RR 0.57, confidence interval 0.28 to 1.19, crossing no effect). NCCIH is equally unimpressed: there is not enough high quality evidence to allow definite conclusions to be reached about the effects of milk thistle on health conditions in people, and results for liver disease have been conflicting or too limited. The decisive negative trial is Fried 2012 in JAMA, the NCCIH funded SyNCH study: 154 people with chronic hepatitis C were given silymarin at doses far above customary supplement levels and it did not reduce ALT or viral load compared with placebo (PMID 22797645). NCCIH notes that although laboratory studies found antiviral, antioxidant and hepatoprotective effects, those benefits were not seen in clinical trials of milk thistle for liver disease. Where it is least bad: in fatty liver disease, meta analyses of small randomised trials report modest reductions in ALT and AST, roughly 9 to 17 U/L, but the trials are of low quality and reviewers judge the clinical relevance limited (PMID 38579127). Blood sugar in type 2 diabetes is limited and is a disease indication anyway. Everything else, including detox, hangovers, skin and general liver support, is insufficient. Europe's regulator registers milk thistle fruit purely on TRADITIONAL use, for digestive complaints and to support liver function, explicitly because there is insufficient evidence from clinical trials. The one place silymarin genuinely earns its reputation is not a supplement use at all: intravenous silibinin is approved in Europe for Amanita phalloides mushroom poisoning, an emergency hospital treatment, and even there LiverTox records only animal models and open label human studies with no prospective controlled trials.
250 to 750 mg of silymarin standardised extract, two to three times daily, is what LiverTox records as the marketed practice. There is no evidence based therapeutic dose, because there is no demonstrated therapeutic effect to dose for. Note that the negative JAMA trial used 420 mg and 700 mg three times daily, well above what any supplement delivers, and still found nothing, so the failure is not a dosing failure.
Take with meals to reduce GI upset. Standardised capsule/tablet preparations preferred over tea (silymarin has poor water solubility). Minimum 4 to 8 weeks for hepatoprotective benefit. Phytosome preparations (silybin phosphatidylcholine) have improved bioavailability.
Onset: ~21 days
Exceptionally well tolerated. GI upset (loose stools, bloating) in <5% of users. Rare allergic reactions, Asteraceae family cross reactivity. Mild CYP3A4 and CYP2C9 inhibition at high doses may affect drugs metabolised by these enzymes (e.g. statins, warfarin, some antiretrovirals), clinical significance is generally low at standard therapeutic doses.
Pregnancy: caution
Breastfeeding: caution
Used for over 2,000 years in European and Mediterranean herbal medicine for liver complaints, digestive bitters, and as a galactagogue. Referenced by Pliny the Elder as a treatment for liver conditions. The active compound silymarin is one of the most studied hepatoprotective plant compounds in modern medicine.
Active compounds: silybin (silibinin), silychristin, silydianin, isosilybin, taxifolin
Remedies using Milk Thistle · Browse by body system · Check it against what you take
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.