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Milk Thistle



Laura Shane-McWhorter

, PharmD, University of Utah College of Pharmacy

Last full review/revision Jul 2020| Content last modified Jul 2020
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Milk thistle (Silybum marianum) is a purple-flowered plant. Its sap and seeds contain the active ingredient silymarin, a potent antioxidant and a term often used interchangeably with milk thistle. Silymarin can be further divided into 3 primary flavonoids: silybin, silydianin, and silychristin. Extracts of milk thistle should be standardized to 80 percent silymarin.


Milk thistle is said to treat cirrhosis and to protect the liver from viral hepatitis, the damaging effects of alcohol, and hepatotoxic drugs (1). Milk thistle may also improve glycemic control in type 2 diabetes (2), and individual case reports claim fatality reduction in mushroom poisoning (3).


A 2007 Cochrane review of 13 randomized clinical trials assessed milk thistle in 915 patients with alcoholic and/or hepatitis B or C virus liver diseases (4). Data from this analysis determined that intervention had no significant effect on all-cause mortality, complications of liver disease, or liver histology. When all trials were included in the analysis, liver-related mortality was significantly reduced; however, in an analysis limited to high-quality studies, this reduction was not significant. Milk thistle was not associated with a significant increase in adverse effects. The design of these clinical trials did come into question, and the authors questioned the benefits of milk thistle and suggested the need for more well-designed placebo-controlled studies.

A meta-analysis of randomized controlled studies of milk thistle for hepatitis C reported that, although well tolerated, it does not provide overall benefit (5). In vitro, silymarin increases levels of intrahepatic glutathione, an antioxidant important for detoxification (6).

A 2018 systematic review and meta-analysis of 7 studies (370 subjects) found that milk thistle significantly decreased fasting glucose by 37.9 mg/dL (2.1 mmol/L) and hemoglobin A1C by 1.4% (2).

In case reports, 2 cases of Amanita mushroom ingestion poisoning (3) showed favorable results after treatment with silybin.

Adverse effects

No serious adverse effects have been reported. Women who have hormone-sensitive conditions (eg, breast, uterine, and ovarian cancer; endometriosis; uterine fibroids) should avoid the above-ground parts of milk thistle.

Drug interactions

Milk thistle may intensify the effects of antihyperglycemic drugs (7) and may interfere with indinavir therapy (8). Silybin inhibits phase 1 and 2 enzymes and inactivates cytochromes P450 3A4 and 2C9.

Milk thistle references

  • Abenavoli L, Izzo AA, Milic N, et al: Milk thistle (Silybum marianum): a concise overview on its chemistry, pharmacological, and nutraceutical uses in liver diseases. Phytother Res 32(11):2202-2213, 2018. doi: 10.1002/ptr.6171.

  • Hadi A, Pourmasoumi M, Mohammadi H, et al: The effects of silymarin supplementation on metabolic status and oxidative stress in patients with type 2 diabetes mellitus: a systematic review and meta-analysis of clinical trials. Complement Ther Med 41:311-319, 2018. doi: 10.1016/j.ctim.2018.08.010. 

  • Ward J, Kapadia K, Brush E, et al: Amatoxin poisoning: case reports and review of current therapies. J Emerg Med 44(1):116-121, 2013.  doi: 10.1016/j.jemermed.2012.02.020.

  • Rambaldi A, Jacobs BP, Gluud C: Milk thistle for alcoholic and/or hepatitis B or C virus liver diseases. Cochrane Database Syst Rev (4)CD003620, 2007. doi: 10.1002/14651858.CD003620.pub3.

  • Yang Z, Zhuang L, Lu Y, et al: Effects and tolerance of silymarin (milk thistle) in chronic hepatitis C virus infection patients: a meta-analysis of randomized controlled trials. Biomed Res Int 941085, 2014. doi: 10.1155/2014/941085.

  • Valenzuela A, Aspillaga M, Vial S, et al: Selectivity of silymarin on the increase of the glutathione content in different tissues of the rat. Planta Med 55(5):420-422, 1989. doi: 10.1055/s-2006-962056.

  • Wu JW, Lin LC, Tsai TH: Drug-drug interactions of silymarin on the perspective of pharmacokinetics. J Ethnopharmacol 121(2):185-193, 2009. doi: 10.1016/j.jep.2008.10.036.

  • Jalloh MA, Gregory PJ, Hein D, et al: Dietary supplement interactions with antiretrovirals: a systematic review. Int J STD AIDS 28(1):4-15, 2017. doi: 10.1177/0956462416671087. 

More Information

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