Milk thistle

What is milk thistle?

Milk thistle (Silybum marianum) is a tall plant with large purple flowers native to Europe and introduced to North America by early colonists. According to the National Center for Complementary and Integrative Health, the main constituent of milk thistle extract is silymarin, a mixture of compounds that includes silybin. Historically, milk thistle was used for liver disorders and to increase breast milk production, and today it is promoted for liver health, diabetes and other conditions.

What the research says

NCCIH summarizes the evidence clearly: there isn’t enough high-quality evidence to allow definite conclusions about milk thistle’s effects on health conditions in people. A small number of studies suggest milk thistle extracts may help control blood sugar in people with type 2 diabetes, but most of that research was done in Middle Eastern countries and it is unclear whether the results apply elsewhere.

For liver conditions, trial results have been conflicting or too limited to draw conclusions. Two NCCIH-funded studies, one in hepatitis C and one in a progressive form of fatty liver disease, did not show benefits from silymarin. It is unclear whether milk thistle affects breast milk production, and its usefulness for other conditions is unknown.

The Claritox Pro reference page links milk thistle to brain protection, citing consumer health articles rather than clinical trials. We found no human research showing that milk thistle supports balance or steadiness. We rate the evidence as limited.

How it’s used in supplements

Milk thistle is sold as capsules of seed extract, usually standardized to 70 to 80 percent silymarin, as well as teas and tinctures.

NCCIH reports that milk thistle taken by mouth appears to be well tolerated, with digestive symptoms such as bloating, nausea and gas being the most common side effects. It may cause allergic reactions in people allergic to related plants such as ragweed, chrysanthemum, marigold and daisy. NCCIH also raises a quality concern: some milk thistle products sold in the US and other countries have contained amounts of silymarin very different from the label, or have been contaminated with pesticides, microorganisms or mycotoxins. Little is known about its safety in pregnancy or breastfeeding.

In Claritox Pro, milk thistle is listed without an amount or standardization, so its silymarin content is unknown.

Given the quality concerns NCCIH describes, anyone who wants to use milk thistle should choose a product that states its silymarin content and shows evidence of independent testing. A blend that lists milk thistle with no amount offers neither.