Milk Thistle Flower seeds, the part used in modern herbalism, contain a group of compounds (flavonolignans) collectively called silymarin.
Silymarin contains compounds like silybin, silychristin, silydianin and isosilybin. It is these compounds that appear to give milk thistle its primary liver benefits. The seeds contain 1.5% to 3% of these compounds, and the industry standard is to selectively extract these compounds to concentrate them rather than use the whole herb. You can find standardized extracts that contain as much as 80% silymarin. This can be convenient, but, you don’t need a standardized extract to get results.
Silymarin has been shown to protect liver cells from chemicals and toxins. Examples of compounds milk thistle will protect the liver from include alcohol, tetracycline, acetaminophen, thallium, erythromycin, amitriptyline, and carbon tetrachloride. It can also reduce side effects from chemotherapy. Silymarin also raises glutathione levels in the liver, which scavenges free radicals also helping to protect the liver.