The active ingredient in milk thistle is called silymarin, which is a flavonoid complex that is extracted from the seeds of the herb.
Sometimes the terms silymarin and milk thistle are used interchangeably and products that are titled after both names are currently popular in the United States and Europe.
The active ingredient, silymarin, is a highly powerful antioxidant.
In these clinical trials and studies, the active ingredient, Silymarin, slowed the growth rate of the some cancerous cells and improved the efficacy of chemotherapy drugs.
One study even showed that the active ingredient, silymarin, was as effective as the cholesterol-lowering drug Probucol, while coming with the added benefit of significantly increasing HDL (good) cholesterol.