Milk Thistle

Author

Nancy Hepp, MS, BCCT Project Manager

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Reviewer

Laura Pole, RN, MSN, OCNS, BCCT Senior Researcher

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Last updated November 20, 2020.

 Also known by these names

  • Carduus marianum
  • Holy thistle
  • Lady's thistle
  • Mary thistle
  • Marian thistle
  • Silibinin
  • Silybum marianum
  • Silymarin

Key Points

  • Before using this therapy, consult your oncology team about interactions with other treatments and therapies. Also make sure this therapy is safe for use with any other medical conditions you may have.
  • Milk thistle may be useful against liver cancer.
  • BCCT’s interest in milk thistle derives from its protective effects, reducing chemotherapy kidney damage in rats and liver toxicity associated with chemotherapy in children with acute lymphoblastic leukemia.
  • Silibinin, one of the flavonoids in milk thistle, has demonstrated antioxidant and anti-inflammatory effects.
  • Silibinin promoted the growth of liver cancer when used with alcohol in an animal study.
  • Milk thistle has shown a few side effects and interactions with prescription drugs.

The natural product milk thistle is available as a supplement. Silymarin, a standardized extract of milk thistle seeds, has shown beneficial effects against liver disease, including stimulating regeneration of liver tissue.1

Treating the Cancer

Working against cancer growth or spread, improving survival, or working with other treatments or therapies to improve their anticancer action

Clinical Evidence

Small studies have investigated effects of silymarin in individuals with prostate cancer, although study results are not yet available.2

Lab and Animal Evidence

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Managing Side Effects and Promoting Wellness

Clinical Evidence

  • Milk thistle may prevent or treat liver dysfunction in patients undergoing anticancer therapy.10 Silymarin has reduced liver toxicity associated with methotrexate (MTX) chemotherapy in children with acute lymphoblastic leukemia (ALL).11
  • Silymarin decreased early doxorubicin-induced left ventricular systolic function disturbances. Study authors concluded that silymarin "can be recommended as adjuvant drug in patients with ALL under doxorubicin therapy."12
  • Silymarin delayed radiodermatitis development and progression in breast cancer patients13
  • Silymarin delayed mucositis development and progression in patients with head and neck cancer.14

Lab and Animal Evidence

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Reducing Risk

Reducing the risk of developing cancer or the risk of recurrence

Lab and Animal Evidence

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Optimizing Your Terrain

Silibinin has demonstrated antioxidant and anti-inflammatory effects in preclinical studies.19

Cautions

Silibinin exerted marginal protective effects in early stages of liver cancer in mice. However, when administered with alcohol (ethanol), it exacerbated the effects of alcohol in promoting liver cancer, but only in males.20

Milk thistle has few side effects or interactions with prescription drugs, but the most commonly reported adverse effects are a mild laxative effect and gastrointestinal upset.21

Silymarin may increase the cytotoxicity of doxorubicin.22

Both silymarin and silibinin may interfere with intestinal glucuronidation of the drug raloxifene, increasing raloxifene exposure and risk for adverse events.23

Milk thistle was associated with a modestly increased incidence of mammary tumors in rats24 but not mice.25

Other cautions are noted on the Memorial Sloan Kettering Cancer Center’s About Herbs website. Medical supervision is recommended.

Access

Milk thistle supplements are widely available.

Dosing

BCCT does not recommend therapies or doses, but only provides information for patients and providers to consider as part of a complete treatment plan. Patients should discuss therapies with their physicians, as contraindications, interactions and side effects must be evaluated.

Levels of active ingredients of natural products can vary widely between and even within products. See Quality and Sources of Herbs, Supplements and Other Natural Products.

Dosage recommendations are available from these sources:

Integrative Programs, Protocols and Medical Systems

For more information about programs and protocols, see our Integrative Programs and Protocols page.

Non-cancer Uses of Milk Thistle

Milk thistle protects against and may even reverse liver damage from alcohol and from some drugs. Milk thistle protects and promotes regeneration of the liver and is used in treating hepatitis. It also protects against Alzheimer’s disease and is used to treat gastrointestinal upset. Milk thistle supplements have shown use in improving glycemic profiles in type II diabetic patients.

BCCT has not reviewed the effectiveness of this therapy for non-cancer uses.

Commentary

A physician  was referred to BCCT with a question about the safety of using milk thistle with anastrozole (Arimidex), and about the impact of milk thistle/Sylbum on the estrogen receptor.

A response from BCCT advisor Jen Green, ND, FABNO, September 1, 2020: Milk thistle seed tea is safe to combine with Arimidex. 

It also would be safe to combine milk thistle as a standardized extract in supplement form (typically 300-900mg is used daily to deal with elevated liver enzymes) because milk thistle does not appear to affect any CYP pathways. Milk thistle is a safe herb that supports liver cell regeneration. It is likely safe concurrent with chemotherapy:

  •  In a randomized controlled trial of children with cancer and liver toxicity, milk thistle was associated with a trend toward significant reductions in liver toxicity. It did not antagonize the effects of chemotherapy agents used.31
  • In clinical studies, milk thistle did not cause significant pharmacokinetic interactions with midazolam, irinotecan, docetaxel and imatinib.32
  • In healthy volunteers, milk thistle did not affect metabolism of CYP2D6 substrates,33 CYP1A2, CYP2D6, CYP2E1, or CYP3A4 substrates.34

As for the impact on estrogen receptors, that likely comes from this review: The natural agonist of estrogen receptor β silibinin plays an immunosuppressive role representing a potential therapeutic tool in rheumatoid arthritis. A few thoughts....in petri dishes, concentrated extract of silybin (low levels in the whole herb) bind to estrogen beta receptors in the same way that soy, flax and other phytoestrogens bind to ERbeta receptors. The blocking of estrogen beta receptors by phytoestrogens is thought to make it harder for ERalpha to be bound by estradiol, which may account for the anti-estrogen effects of phytoestrogens in human studies evaluating breast tissue (ie. lower breast density).

That being said, milk thistle has never been historically considered an herb that impacts hormone balance, so I strongly suspect that it doesn't have the ERbeta binding ability that many other herbs and foods do. The main action of milk thistle is to decrease inflammation (VEGF specifically), and support liver cell regeneration.

BCCT has not conducted an independent review of research of milk thistle. This summary draws from the Memorial Sloan Kettering Cancer Center’s About Herbs and CAM-Cancer Summaries websites plus other sources as noted.

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