Milk Thistle
Milk thistle and silymarin: what NIH says about liver disease, blood sugar and other uses, side effects, allergy risks and product quality concerns.
Content last updated . This page has not been medically reviewed.
Safety first. Supplements can cause side effects and interact with medicines. Read mushroom safety and interactions before you use any mushroom product.
Overview
Milk thistle is a tall plant with large purple flowers, native to Europe and introduced to North America by early colonists. Its main constituent in extracts is silymarin, a mixture of compounds. Historically it was used for liver disorders and to increase breast milk production, and it is promoted as a supplement for liver disorders, diabetes and other conditions. [1]Names and parts
Silybum marianum (synonym Carduus marianus), also called Mary thistle. [1][2] Supplements are usually standardized extracts of the seed, measured for silymarin. A percentage on a label measures silymarin, not benefit. See Quality.What the research shows (NIH summary)
NIH says there is not enough high-quality evidence for definite conclusions. [1]| Use | What NIH says | Strength of evidence |
|---|---|---|
| Blood sugar in type 2 diabetes | A small number of studies show extracts may help control blood sugar. Most research was done in Middle Eastern countries, and it is unclear whether results would be the same elsewhere. [1] | Limited |
| Liver diseases (alcohol-related, hepatitis B and C, fatty liver, chemotherapy-related and others) | Results have been conflicting or too limited. Two studies funded by NCCIH, one on hepatitis C and one on a progressive form of fatty liver disease, did not show benefits from silymarin. [1] | Conflicting |
| Breast milk production | Unclear whether it has an effect. [1] | Unclear |
Safety
- Taken by mouth it appears well tolerated. The most common side effects are digestive: bloating, nausea and gas. [1]
- It may cause allergic reactions, especially in people allergic to related plants such as ragweed, chrysanthemum, marigold and daisy. [1]
- Concerns have been raised about poor chemical and microbiological quality of milk thistle supplements sold in the US and elsewhere: some contained silymarin amounts substantially different from the label or were contaminated with pesticides, microorganisms or mycotoxins. [1]
- Little is known about safety in pregnancy or breastfeeding. [1]
- Ask a pharmacist about medicine interactions. NIH does not list any on this page.
Frequently asked questions
Does milk thistle detox or repair the liver?
NIH says liver disease trial results have been conflicting or too limited, and two NIH-funded trials showed no benefit. [1]
Is milk thistle safe if I am allergic to ragweed?
It may cause allergic reactions, particularly in people allergic to related plants such as ragweed. [1]
References
- National Center for Complementary and Integrative Health (NIH). Milk Thistle: Usefulness and Safety. Page last updated February 2025.
- GBIF Secretariat. GBIF Backbone Taxonomy. Names checked 2026-10-22 through the GBIF species match service.
Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.