Milk thistle

Milk thistle is a plant that comes from the same group of flowers as the daisy. It is not a treatment for cancer.


  • The medicinal compound in milk thistle is silymarin, an extract of milk thistle seeds.
  • Milk thistle might help to treat some liver diseases such as hepatitis and cirrhosis.
  • More research is needed before we will know if milk thistle can help prevent or treat cancer. 

What is milk thistle?

The fruit and seeds of the milk thistle plant have been used for hundreds of years as a herbal remedy for some liver problems. 

The scientific name for milk thistle is silybum marianum. It is also called holy thistle, Marian thistle, Mary thistle, St. Mary thistle, Our Lady's thistle, wild artichoke, Mariendistel (German), and Chardon-Marie (French). 

The medicinal compound in milk thistle is silymarin, an extract of milk thistle seeds. It is an antioxidant that protects against cell damage.

Silymarin contains 4 compounds, including silybin (the most active), isosilybin, silychristin, and silydianin. Most research has studied silymarin or its major compound silybin, instead of the plant as a whole.

How you have it

Milk thistle supplements are available as capsules, tablets, powder, and liquid extract.

Powdered milk thistle can be made into a tea. 

Side effects

Although taking milk thistle is generally considered safe, we would recommend anyone thinking of taking it to talk to their doctor first. 

Women who are pregnant or breast feeding should not take this herb. If you are diabetic you should consult your doctor first. 

Milk thistle can cause diarhoea, feeling sick, heartburn and stomach upset.

If you have liver problems you should consult your doctor first. High doses of the herb can cause elevated levels of bilirubin and liver enzymes. 

We don't yet have enough research to know whether milk thistle may affect cancer treatments and make them more or less effective. 

Generally antioxidant supplements are not recommended during chemotherapy or radiotherapy treatment, because they may block some of the cancer killing effects of these treatments.

Research into milk thistle and cancer

Research in the laboratory has shown that milk thistle might help to treat some liver diseases, such as hepatitis and cirrhosis. 

A few trials have looked at milk thistle for people with cancer.

A number of companies on the internet claim that milk thistle can help to detoxify and protect your liver. They also claim that it can help to protect other organs of the body such as the gallbladder and spleen.

Some claim that it slows the growth of some types of cancer, including breast and prostate cancer. Although it is possible that milk thistle may play a part in treating liver disease and some types of cancer there is currently not enough evidence for this.

We need a lot more research with reliable clinical trials before we can be sure that milk thistle will play any part in treating or preventing cancers.

A word of caution

Make sure you check with your cancer specialist before you start taking milk thistle. They are in the best position to advise you, as they know about your individual situation. 

Last reviewed: 
09 May 2019
  • National Cancer Institute (NCI).

  • Topical silymarin administration for prevention of acute radiodermatitis in breast cancer patients: A randomized, double‐blind, placebo‐controlled clinical trial

    H. Karbasforooshan and others. Phytotherapy Research, February 2019, Vol 33, Issue 2; pages 379-386

  • A randomized, controlled, double-blind, pilot study of milk thistle for the treatment of hepatotoxicity in childhood acute lymphoblastic leukemia (ALL). E.J Ladas and others. Cancer. Jan 2010. Vol 116(2) pages 506-13.

  • Milk thistle for alcoholic and/or hepatitis B or C virus liver diseases. A. Rambaldi. The Cochrane database of systematic reviews, 17 Oct 2007;(4)

  • Effect of Milk Thistle (Silybum marianum) on the Pharmacokinetics of Irinotecan. P.H Nielka and others, Clinical Cancer Research, November 2005.
    Volume 11, Issue 21

  • Complete Guide to Complementary and Alternative Cancer Therapies (2nd Edition)
    American Cancer Society, 2009

  • The information on this page is based on literature searches and specialist checking. We used many references and there are too many to list here. If you need additional references for this information please contact with details of the particular issue you are interested in.

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