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Milk thistle (Silybum marianum) is a flowering herb in the Asteraceae family that has been used medicinally for over 2,000 years. Its primary active component is silymarin, a complex of flavonolignans that includes silybin (also called silibinin), silychristin, and silydianin. Silybin is considered the most biologically active component, typically comprising about 50-70% of silymarin extracts.
Image source and license: https://commons.wikimedia.org/wiki/File:Silybum_marianum_kz13.jpg.
Modified by Peter Jorgensen.
Milk thistle is known by several common names including blessed milk thistle, Marian thistle, Mediterranean milk thistle, variegated thistle, and St. Mary's thistle. Its botanical name is Silybum marianum (L.) Gaertn. It should not be confused with other thistles like Scotch thistle (Onopordum acanthium), blessed thistle (Cnicus benedictus), or holy thistle (which can refer to Silybum marianum but also sometimes to Cnicus benedictus), despite similar-sounding names.
Milk thistle has been studied for numerous health conditions, with varying levels of scientific support. The following represent conditions for which there is moderate to strong evidence:
Conditions with preliminary or limited evidence include:
It is important to note that milk thistle has not been conclusively proven to "cure" any disease, despite showing therapeutic potential in managing or alleviating symptoms of various conditions.
Clinical studies have used various dosages depending on the condition being treated. Most commonly:
Most commercial preparations are standardized to contain 70-80% silymarin. Products with higher silybin content (the most active component) may be more effective at lower doses. Phosphatidylcholine formulations and silybin-phytosome complexes have demonstrated improved bioavailability.
Milk thistle is generally considered safe for most people when used at recommended dosages. However, reported side effects include:
Pregnant and breastfeeding women should avoid milk thistle due to insufficient safety data. Those with hormone-sensitive conditions (certain breast, uterine, or ovarian cancers, endometriosis, uterine fibroids) should consult healthcare providers before use due to possible estrogenic effects.
Studies investigating doses above the typical therapeutic range (>800 mg silymarin daily) are limited. In trials examining higher doses:
Significant knowledge gaps exist regarding:
Several pharmaceutical-grade products containing milk thistle extracts are available globally, though availability varies by country:
Most milk thistle products are classified as dietary supplements rather than pharmaceuticals, thus subject to less rigorous regulatory standards.
Abenavoli, L., Izzo, A. A., Milić, N., Cicala, C., Santini, A., & Capasso, R. (2018). Milk thistle (Silybum marianum): A concise overview on its chemistry, pharmacological, and nutraceutical uses in liver diseases. Phytotherapy research, 32(11), 2202-2213.
de Avelar, C. R., Pereira, E. M., de Farias Costa, P. R., de Jesus, R. P., & de Oliveira, L. P. M. (2017). Effect of silymarin on biochemical indicators in patients with liver disease: Systematic review with meta-analysis. World journal of gastroenterology, 23(27), 5004.
Gillessen, A., & Schmidt, H. H. J. (2020). Silymarin as supportive treatment in liver diseases: A narrative review. Advances in therapy, 37(4), 1279-1301.
Kalopitas, G., Antza, C., Doundoulakis, I., Siargkas, A., Kouroumalis, E., Germanidis, G., ... & Chourdakis, M. (2021). Impact of Silymarin in individuals with nonalcoholic fatty liver disease: A systematic review and meta-analysis. Nutrition, 83, 111092.
Karimi, G., Vahabzadeh, M., Lari, P., Rashedinia, M., & Moshiri, M. (2011). “Silymarin”, a promising pharmacological agent for treatment of diseases. Iranian journal of basic medical sciences, 14(4), 308.
Kawaguchi-Suzuki, M., Frye, R. F., Zhu, H. J., Brinda, B. J., Chavin, K. D., Bernstein, H. J., & Markowitz, J. S. (2014). The effects of milk thistle (Silybum marianum) on human cytochrome P450 activity. Drug Metabolism and Disposition, 42(10), 1611-1616.
Marmouzi, I., Bouyahya, A., Ezzat, S. M., El Jemli, M., & Kharbach, M. (2021). The food plant Silybum marianum (L.) Gaertn.: Phytochemistry, Ethnopharmacology and clinical evidence. Journal of Ethnopharmacology, 265, 113303.