Summary
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What does milk thistle do?
For people with type 2 diabetes, milk thistle may decrease blood sugar, hemoglobin A1c, and LDL cholesterol levels when used with conventional therapy. The evidence is mixed as to whether it improves liver function in people with chronic active hepatitis (see What It Does). -
What is silymarin?
Silymarin is the term for a specific group of chemically-related compounds found in milk thistle. Silymarin is thought to be responsible for some of the herb's effects and is used as a marker of milk thistle strength (see What It Is). -
What to look for with milk thistle?
Milk thistle comes in various forms and concentrations, but most clinical studies of milk thistle's effectiveness have used extracts at a dose of about 200 mg of extract taken 2 to 3 times per day. The amount of silymarin in these extracts is about 58% of its weight (although this has been reported as 80% when using a non-specific, older method of testing known as UV-VIS) (see What to Consider When Buying and Using for dosage and other details). -
What did CL find in its tests of milk thistle supplements?
The amount of silymarin per serving ranged from 61.2 mg to 202 mg. For most products, these amounts were far less than a consumer might expect from labels, leading CL to rate several products as having poor labeling (see What CL Found). 
Which is the best milk thistle supplement?
Among products Approved for Quality by ConsumerLab.com one was chosen as CL's Top Pick for providing a substantial amount of silymarin, appropriate usage instructions, and superior value.-
What are the side effects of milk thistle?
Milk thistle is generally well tolerated but, infrequently, can have a laxative or other gastrointestinal side-effect. Allergic reactions can occur, especially in people who are sensitive to related plants and it may interact with certain medications. People with liver disease should avoid milk thistle sold as whole seed, cut herb, or powders, which have the potential to be contaminated with yeast and mold (fungi) that can produce toxins harmful to the liver (see Concerns and Cautions).
