What is milk thistle?
Milk thistle is a plant that contains silymarin, a substance that improves liver function. Originally from Europe, milk thistle now also grows in North America.
You can take milk thistle in capsules or as a tincture (combined with alcohol). It has been widely used in Europe and Germany, where it is a common complementary treatment for liver problems such as hepatitis and cirrhosis. In Canada, it is sold as a natural health product.
What is milk thistle used for?
People use milk thistle as a complementary treatment for liver problems, particularly hepatitis and cirrhosis and inflammation of the bile ducts (cholangitis). Research on silymarin suggests that it may protect the liver from inflammation. But it does not have a direct effect on viruses that cause hepatitis, such as the hepatitis C virus.footnote 1
Preliminary research suggests that silymarin is an antioxidant, which helps protect the body from cell-destroying substances called free radicals. Silymarin also may reduce inflammation and block the effects of toxins that harm the liver.footnote 2
Two studies on milk thistle presented conflicting results. One study found that milk thistle appeared to help some people with cirrhosis live longer than they would have otherwise, while another found no benefit.footnote 2
Is milk thistle safe?
Milk thistle may cause nausea, diarrhea, bloating, pain, or allergies.
The Natural and Non-Prescription Health Products Directorate (NNHPD), within the Health Products and Food Branch of Health Canada, regulates natural health products in Canada. Natural health products, including milk thistle, must be reviewed and approved by the NNHPD before they can be sold in Canada.
Always tell your doctor if you are using a natural health product or if you are thinking about combining a natural health product with your conventional medical treatment. It may not be safe to forgo your conventional medical treatment and rely only on a natural health product. This is especially important for women who are pregnant or breastfeeding.
When using natural health products, keep in mind the following:
- Like conventional medicines, natural health products may cause side effects, trigger allergic reactions, or interact with prescription and non-prescription medicines or other natural health products you might be taking. A side effect or interaction with another medicine or natural product may make other health conditions worse.
- Natural health products may not be standardized in their manufacturing. This means that how well they work or any side effects they cause may differ among brands or even within different lots of the same brand. The form you buy in health food or grocery stores may not be the same as the form used in research.
- Other than in vitamins and minerals, the long-term effects of most natural health products are not known.
- National Center for Complementary and Alternative Medicine (2012). Get the facts. Hepatitis C: A focus on dietary supplements. (NCCAM Publication No. D422). Available online: http://nccam.nih.gov/health/hepatitisc/hepatitiscfacts.htm?nav=gsa.
- Murray MT (2013). Silybum marianum (milk thistle). In JE Pizzorno, MT Murray, eds., Textbook of Natural Medicine, 4th ed., pp. 1026–1031. St. Louis: Mosby.
Other Works Consulted
- Milk thistle (2010). In A DerMarderosian et al., eds., Review of Natural Products. St. Louis: Wolters Kluwer Health.
Current as of: December 20, 2019
Author: Healthwise Staff
Medical Review: Adam Husney, MD - Family Medicine
Brian O'Brien, MD, FRCPC - Internal Medicine
Kathleen Romito, MD - Family Medicine
Current as of: December 20, 2019