Silybin (Silibinin · Flavonolignan · Hepatoprotective · Liver RCT Evidence)

Compound	Silybin (Silibinin; Silibin; Silybin A + Silybin B diastereomers; primary silymarin component)
Chemical class	Polyphenol — Flavonolignan (taxifolin esterified with coniferyl alcohol via an ether bond; unique hybrid class)
CAS	22888-70-6
Primary source	Silybum marianum (milk thistle seeds — 50–60% of the silymarin complex)
Key applications	Hepatoprotective (NAFLD, alcoholic liver disease, drug-induced liver injury); antioxidant; antifibrotic; anti-inflammatory
Claim strength	High
Typical form	Organic Milk Thistle Extract Powder (Silybum marianum, standardised to silymarin ≥70–80%); Milk Thistle Seed Liquid Extract; Oil Soluble Extract
Buy from Herbuno	Organic Milk Thistle (Silybum marianum) Extract Powder → Milk Thistle Seed Liquid Extract (Water Soluble) - Silybum marianum →

Name origin: Silybin is named after Silybum marianum — the milk thistle — with the characteristic "-bin" suffix reflecting its early isolation nomenclature. It is also called silibinin (the INN pharmaceutical name). Silybin is the primary and most pharmacologically active component of silymarin — the standardised milk thistle seed extract mixture that also contains silychristin, silydianin, and isosilybin. Silybin itself exists as two diastereomers (Silybin A and Silybin B, the 2R,3R and 2S,3S configurations) — both are hepatoprotective, though Silybin B appears more potent in some assays. Traditional use: Milk thistle (Silybum marianum) has one of the longest recorded medicinal histories of any liver herb — Pedanius Dioscorides described its use for liver protection in De Materia Medica (70 CE), and it appears in all major European herbals through the Renaissance. Culpeper's Complete Herbal (1653) describes it for "removing obstructions of liver and spleen." German Commission E approved silymarin-standardised milk thistle seed preparations for liver complaints in 1986 — one of the earliest phytomedicine regulatory approvals in Germany. Research trajectory: Silymarin/silybin has the largest evidence base of any plant-derived hepatoprotective compound — with multiple RCTs in NAFLD, alcoholic liver disease, hepatitis C, and drug-induced liver injury (DILI). The European liver medicine community (EASL) recognises silymarin as a complementary therapy for chronic liver diseases. The intravenous formulation (Legalon® SIL) is used for acute Amanita phalloides (death cap mushroom) poisoning in European emergency medicine. Commercial source: Organic Milk Thistle Extract Powder and Milk Thistle Seed Liquid Extract (both Silybum marianum) are available from Herbuno — standardised to silymarin content with silybin as the dominant constituent.

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Evidence for Silybin Applications

Hepatoprotective — NAFLD: A meta-analysis of 10 RCTs (Zhong et al. 2017) demonstrated that silymarin/silybin supplementation significantly improves ALT, AST, GGT, total cholesterol, and liver steatosis grade in NAFLD patients. Individual RCTs using Legalon® 70 (silymarin 140 mg three times daily = 420 mg silymarin/day) over 6–12 months show consistent ALT normalisation rates higher than placebo. Silybin-phosphatidylcholine complex (Siliphos®/Realsil®) shows superior bioavailability and efficacy versus standard silymarin in comparative NAFLD trials. Claim strength: High.

Hepatoprotective — alcoholic liver disease: Multiple controlled trials demonstrate silymarin's efficacy in reducing ALT/AST elevation, improving liver histology, and reducing liver-related mortality in alcoholic liver disease. The mechanism involves antioxidant (scavenging ROS from alcohol metabolism), anti-inflammatory (NF-κB suppression), and membrane-stabilising (silybin inserts into hepatocyte membranes, reducing membrane permeability to hepatotoxins) activities. Claim strength: High.

Drug-induced liver injury (DILI) prevention: Silybin IV (Legalon® SIL) is used for Amanita phalloides poisoning — amanitin toxin causes severe DILI by inhibiting RNA polymerase II; silybin competitively inhibits hepatic uptake of amanitin via OATP1B3 transporter blockade. In conventional DILI (from pharmaceuticals), silymarin supplementation during hepatotoxic drug therapy (chemotherapy, antituberculosis drugs) shows liver enzyme-protective effects in multiple RCTs. Claim strength: High (Amanita poisoning); Moderate (conventional DILI).

Antifibrotic: Silybin inhibits hepatic stellate cell (HSC) activation — the primary mechanism of liver fibrosis — via TGF-β1/Smad signalling suppression and PDGF receptor inhibition. In preclinical models, silybin at pharmacological doses significantly reduces hepatic collagen deposition. Clinical antifibrotic evidence is preliminary — improved fibrosis markers in some hepatitis C clinical trials. Claim strength: Moderate.

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Dosage & Formulator Specification

The most extensively studied dosing for NAFLD and alcoholic liver disease is silymarin 420 mg/day (140 mg three times daily as Legalon® 70) — equivalent to approximately 210–252 mg silybin/day (silybin ~50–60% of silymarin complex). Higher doses (600–1400 mg silymarin/day) are used in hepatitis and DILI studies. The silybin-phosphatidylcholine complex (Siliphos® 1:2 ratio; 100–200 mg twice daily = 200–400 mg complex providing ~67–133 mg silybin equivalent) shows significantly enhanced bioavailability and is the preferred formulation in European clinical practice.

For Herbuno formulator specification: Organic Milk Thistle Extract Powder standardised to ≥70–80% silymarin delivers silybin as the primary constituent (~40–50% of total extract weight = silybin). Milk Thistle Oil Soluble Extract delivers silymarin in a lipid matrix, naturally improving bioavailability for softgel applications. For maximum bioavailability, phospholipid complexation of milk thistle extract at 1:1 or 1:2 silybin-to-phosphatidylcholine ratio is the pharmaceutical gold standard.

Standard milk thistle extract has poor oral bioavailability of silybin due to low water solubility and rapid glucuronidation. Bioavailability enhancement options: phospholipid complex (3–5-fold improvement); nanoemulsion (2–4-fold); self-emulsifying drug delivery system (SEDDS, 2–3-fold); cyclodextrin complex (2–3-fold). For basic supplement formulations, providing silymarin with a fatty meal significantly improves absorption.

Silymarin is extremely well-tolerated — rare mild GI side effects (loose stool, mild nausea) at high doses. No significant drug interactions are established at supplement doses. Note: silybin is metabolised by CYP3A4 and CYP2C9 — theoretical interactions with substrates of these enzymes at very high doses, though clinically significant interactions at standard supplement doses are not documented.

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Frequently Asked Questions — Silybin

What is the difference between silybin, silymarin, and milk thistle extract?
Milk thistle seed extract: the crude botanical extract. Silymarin: the standardised flavonolignan complex from milk thistle seed — typically ≥70% silymarin content, comprising silybin A + B (~50–60%), silychristin (~20%), silydianin (~10%), and isosilybin (~5%). Silybin: the primary and most pharmacologically studied component of silymarin — the individual flavonolignan responsible for most of silymarin's hepatoprotective activity. Silybin A and Silybin B are two diastereomers; their combined content is reported as "silybin" in most standardisation methods.

How does silybin protect the liver at the molecular level?
Silybin's hepatoprotective mechanisms include: (1) membrane stabilisation — silybin inserts into hepatocyte membranes, reducing permeability to hepatotoxins (amatoxins, ethanol metabolites); (2) antioxidant — scavenging ROS produced by cytochrome P450 metabolism of hepatotoxic drugs and alcohol; (3) anti-inflammatory — NF-κB inhibition and TNF-α suppression reducing inflammatory hepatocyte injury; (4) pro-regenerative — promoting hepatocyte protein synthesis (RNA polymerase I activation) and stimulating DNA synthesis in regenerating hepatocytes; (5) antifibrotic — inhibiting hepatic stellate cell activation via TGF-β1/Smad pathway suppression.

Why is the phospholipid complex (Siliphos®) more effective than standard milk thistle extract?
Standard silybin has poor water solubility and poor membrane permeability — limiting oral bioavailability to ~1–3% of the dose. Complexation with phosphatidylcholine (lecithin) creates an amphiphilic complex that dramatically improves micellar solubilisation in the GI tract and facilitates transcellular absorption through intestinal epithelium. Human pharmacokinetic studies show 3–5-fold higher silybin plasma AUC for the phospholipid complex versus standard silymarin at equivalent silybin doses. Multiple clinical trials (Italian NASH study, Russian hepatitis C study) demonstrate superior clinical efficacy for the phospholipid complex.

Is milk thistle safe during chemotherapy and should oncology patients use it?
Silymarin has been studied as hepatoprotective support during chemotherapy (particularly hepatotoxic regimens like cisplatin, doxorubicin) in multiple RCTs — showing reduced ALT/AST elevation without interfering with chemotherapy efficacy. However, this should be used only with oncologist awareness: silybin modestly inhibits CYP3A4 and UGT enzymes at high doses, potentially affecting pharmacokinetics of specific chemotherapy drugs. The standard clinical approach is professional assessment of the specific chemotherapy regimen and silybin interaction profile before recommending co-administration.

Related compounds: Silychristin, Silydianin, Ampelopsin, Taxifolin

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Claim-strength scale – High = multiple human RCTs; Moderate = limited trials or strong preclinical convergence; Emerging = early-stage lab or animal data.

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