The Sunlight Experiment

Compound Monograph

Silymarin

Silymarin — the flavonolignan complex of milk thistle seed, the best-studied of the herb's constituents and the principal driver of its hepatoprotective, antioxidant, antifibrotic, and antiviral activity.

Work in progress

Classification

Silymarin is a flavonolignan complex, part of the phenolics class. Antioxidant compounds built around one or more phenol rings — the flavonoids, tannins, phenolic acids, coumarins, and pigments behind much of a plant's protective chemistry.

Phenolics Lignans

Where Does It Come From? (3)

Silymarin is a naturally occurring flavonolignan complex, found in Milk Thistle and 2 other sources. It is well tolerated orally (low toxicity).

Globe Artichoke Cynara scolymus Milk Thistle Silybum marianum Milk thistle relatives

Research & Evidence

Silymarin is not a single molecule but a complex of at least seven flavonolignans concentrated in milk thistle seed (it is reported to be absent from the leaves) 3Reference 3Powers J · 2014ReviewSilybum marianum Monograph. It is the most studied of the herb’s constituents and is credited with most of milk thistle’s hepatoprotective activity 1Reference 1Hoffmann · 2003Medical Herbalism: The Science and Practice of Herbal Medicine.

The milk thistle monograph in this database attributes the following to silymarin and its components:

  • Hepatoprotective — the flavonolignan fraction protects the liver against a wide range of insults, including carbon tetrachloride, ethanol, paracetamol, cyclosporin, phenothiazine, erythromycin, amitriptyline, nortriptyline, Amanita phalloides, tacrine, and iron overload 3Reference 3Powers J · 2014ReviewSilybum marianum Monograph. Systematic and Cochrane reviews have examined silymarin/milk thistle in alcoholic and hepatitis B or C liver disease 7,8Reference 7Rambaldi A et al. · 2005Meta-analysisMilk thistle for alcoholic and/or hepatitis B or C liver diseases — a systematic cochrane hepato-biliary group review with meta-analyses of randomized clinical trialsReference 8Mayer KE et al. · 2005Systematic reviewSilymarin treatment of viral hepatitis: a systematic review.
  • Antioxidant — it scavenges free radicals, raises intracellular glutathione, reduces lipid peroxidation, and increases catalase activity 2Reference 2Bone K · 2013Principles and Practice of Phytotherapy.
  • Antifibrotic — silymarin retards collagen accumulation in biliary fibrosis 6Reference 6Boigk G et al. · 1997AnimalSilymarin retards collagen accumulation in early and advanced biliary fibrosis secondary to complete bile duct obliteration in rats and acts through NF-κB inhibition and modulation of hepatic stellate cell activation 2Reference 2Bone K · 2013Principles and Practice of Phytotherapy.
  • Anti-inflammatory / antiviral — standardised silymarin inhibits T-cell inflammatory cytokine production, hepatocyte NF-κB signalling, and HCV infection in vitro 4Reference 4Polyak SJ et al. · 2007Inhibition of T-cell inflammatory cytokines, hepatocyte NF-kappaB signaling, and HCV infection by standardized Silymarin, and silymarin has been shown to inhibit T-cell proliferation and cytokine production in hepatitis C 5Reference 5Morishima C et al. · 2010In vitroSilymarin Inhibits In Vitro T-Cell Proliferation and Cytokine Production in Hepatitis C Virus Infection.
  • Other liver actions — competitive inhibition of the phalloidin-transporting system, toxin blockade via the mitochondrial membrane, enhanced RNA synthesis and cellular regeneration, and improvement of glucose and lipid metabolism are also reported 2,3Reference 2Bone K · 2013Principles and Practice of PhytotherapyReference 3Powers J · 2014ReviewSilybum marianum Monograph.

On absorption, the source notes silymarin is not water-soluble (so it is ineffective as a tea) and is best taken as a standardised extract of 70–80% silymarin 3Reference 3Powers J · 2014ReviewSilybum marianum Monograph; absorption ranges from roughly 20–50% in humans, peaking in the blood about two hours after an oral dose with a half-life near six hours 3Reference 3Powers J · 2014ReviewSilybum marianum Monograph. Lecithin has been reported to enhance its absorption in vivo 2Reference 2Bone K · 2013Principles and Practice of Phytotherapy.

Toxicity & Safety

The source monograph reports no contraindications for milk thistle and describes it as well tolerated. The principal caution relates to silymarin’s up-regulation of liver detoxification, which may increase the onset or potency of prodrugs (such as codeine) and reduce the effectiveness of drugs metabolised by the liver; caution is therefore advised alongside medications 2Reference 2Bone K · 2013Principles and Practice of Phytotherapy. No toxicity figures specific to isolated silymarin are given in the source.

References

  1. Hoffmann, D. (2003). Medical Herbalism: The Science and Practice of Herbal Medicine. Rochester, VT: Healing Arts Press. (Pg. 584).
  2. Bone K, Mills S. (2013). Principles and Practice of Phytotherapy. Elsevier Health, China. (Pg. 861–882).
  3. Powers J. (2014). Silybum marianum Monograph. JATMS, 20(1).
  4. Polyak SJ, Morishima C, Shuhart MC, et al. (2007). Inhibition of T-cell inflammatory cytokines, hepatocyte NF-kappaB signaling, and HCV infection by standardized Silymarin. Gastroenterology, 132, 1925–1936.
  5. Morishima C, Shuhart MC, Wang CC, et al. (2010). Silymarin Inhibits In Vitro T-Cell Proliferation and Cytokine Production in Hepatitis C Virus Infection. Gastroenterology, 138, 671–681.
  6. Boigk G, Stroedter L, Herbst H, et al. (1997). Silymarin retards collagen accumulation in early and advanced biliary fibrosis secondary to complete bile duct obliteration in rats. Hepatology, 26, 643–649.
  7. Rambaldi A, Jacobs BP, Iaquinto G, Gluud C. (2005). Milk thistle for alcoholic and/or hepatitis B or C liver diseases — a systematic cochrane hepato-biliary group review with meta-analyses of randomized clinical trials. Am J Gastroenterol, 100, 2583–2591.
  8. Mayer KE, Myers RP, Lee SS. (2005). Silymarin treatment of viral hepatitis: a systematic review. J Viral Hepat, 12, 559–567.