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Milk thistle seeds contain a bioflavonoid complex known as Silymarin which is the active ingredient. The purified extract of the fruit is what is used in supplements. Studies have looked at the effect of milk thistle on toxic liver damage (mostly alcohol-related) and many other uses. It is concluded that milk thistle is a very useful medicinal plant product that stabilizes the cell membrane and stimulates protein synthesis while accelerating the process of regeneration in damaged liver tissue.
Other studies show that milk thistle may protect the cells of the liver by blocking the entrance of harmful toxins and helping remove these toxins from liver cells. Like many flavonoids, milk thistle is a potent antioxidant which works to maintain health and energy by protecting the body from damage caused by free radicals and lipid peroxidation, which can injure healthy cells and tissues.