ConsumerLab Tests Identify Best Milk Thistle Supplements

White Plains, NY, September 12, 2025 – Some milk thistle supplements may contain far less silymarin than a consumer might expect from labels, according to recent ConsumerLab tests.

Silymarin is a key milk thistle compound used as a marker of milk thistle strength, as it is thought to be responsible for some of the herb’s potential effects, such as lowering blood sugar or improving liver function.

Some Milk Thistle Supplements Provide Little Silymarin

The tests revealed that two of the six milk thistle supplements selected for testing contained only 40% to 60% of the silymarin that ConsumerLab expected based on their labels. In addition, the amount of silymarin across all products ranged 2,800%, from 17.4 mg to 498 mg per daily serving, while most clinical studies of milk thistle's effectiveness have used approximately 200 mg of silymarin taken 2 to 3 times per day.

How Silymarin is Measured Matters

“We also found that the amount of silymarin listed on product labels may be overstated when companies use older testing methods,” said ConsumerLab's President, Tod Cooperman, M.D. “This was the case with one product, which we found to contain just 60% of the silymarin expected from its label when using the more recent and accurate method that is specific to silymarin.”

ConsumerLab uses the official testing method for silymarin published by the United States Pharmacopeia (USP), an organization that sets official quality standards for dietary supplements.

ConsumerLab’s Top Pick

Among supplements that passed testing and were Approved for quality, ConsumerLab selected one as its Top Pick milk thistle supplement that provides a substantial amount of silymarin, appropriate usage instructions, and superior value.

Access the Full Report:

ConsumerLab’s full Milk Thistle Supplements Review can now be accessed online by ConsumerLab.com members –currently over 100,000 individual subscribers and thousands more with access through libraries, schools, and medical centers.

The Milk Thistle Supplements Review includes test results and comparisons for seven milk thistle supplements. Six products were selected for testing by ConsumerLab: BulkSupplements.com Glycine powder, Designs for Health Glycine Powder, Double Wood Supplements Glycine 1,000 mg, Life Extension Glycine 1,000 mg, NOW Glycine powder, NOW Glycine 1,000 mg, Nutricost Glycine – Unflavored powder, Pure Encapsulations Glycine capsules, Swanson Glycine Powder, and Thorne Glycine capsules. Three additional products passed the same testing and were Approved through CL's voluntary Quality Certification Program: 1MD Nutrition LiverMD.

As discussed in the Review, there is some evidence that silymarin from milk thistle improves measures of short-term (fasting blood glucose) and long-term blood sugar control (HbA1c) in people with type 2 diabetes. Milk thistle is also thought to act as a liver protectant and may help to lower elevated liver enzymes in people with metabolic dysfunction-associated steatotic liver disease, although there is no strong evidence that it helps with viral or chronic hepatitis. The Review also explains the differences between milk thistle extracts and seed powders, dosages for specific uses, and safety, side effects, and drug interactions with milk thistle supplements.

Founded in 1999, ConsumerLab.com is a leading provider of consumer information and independent evaluations of products that affect health and nutrition. It has reviewed over 7,000 products and has published Product Reviews covering nearly every popular category of dietary supplements and health foods.

Membership to ConsumerLab.com is available online and provides immediate access to continually updated reviews of nearly every popular type of dietary supplement and health food, answers to reader questions, and product recalls and warnings. ConsumerLab also provides independent product testing through its voluntary Quality Certification Program. The company is privately held and based in New York. It has no ownership from, or interest in, companies that manufacture, distribute, or sell consumer products.