Milk thistle contains multiple constituents with strong antioxidant activity that can protect liver cells from free radical damage, strengthen liver cell membranes, and help maintain the liver's built-in antioxidant system – glutathione and superoxide dismutase (SOD). In numerous studies, the milk thistle constituent silybin – the most active flavonoid in milk thistle – has been utilized to prevent liver cell damage from carbon tetrachloride, ethanol, acetaminophen, mushroom toxins, and benzopyrene from automobile exhaust. Thorne's Siliphos provides the benefits of silybin and phosphatidylcholine in one well-absorbed compound. These ingredients likely provide the synergistic benefit of sparing liver cells from degradation. Studies indicate this silybin-phosphatidylcholine complex provides superior absorption compared to conventional milk thistle products.

Silybin, normally a water-soluble flavonoid, is converted into a lipid-soluble compound by complexing it with phospholipids, such as phosphatidylcholine, to make a phytosome. The phytosome preparation allows for better absorption of this liver-protective flavonoid into liver cell membranes.

Silymarin has been shown to help maintain the liver's normal inflammatory response to liver-toxic compounds. Of the three flavonoids that comprise silymarin, silybin predominates and is the most biologically active of the three.

Phosphatidylcholine is not merely a passive "carrier" for the active flavonoid silybin, but is itself an active ingredient with documented efficacy for promoting liver health. Silybin protects the liver because of its significant antioxidant activity, while phosphatidylcholine helps repair and replace liver cell membranes.