Cholestyramine lowers LDL-C primarily by which mechanism?

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Cholestyramine works as a bile acid sequestrant. Its primary mechanism is to bind bile acids in the intestinal lumen, forming an insoluble complex that's excreted in the stool. This prevents reabsorption of bile acids (reducing enterohepatic circulation) and lowers the hepatic bile acid pool. In response, the liver increases conversion of cholesterol to new bile acids and upregulates LDL receptors to pull more LDL cholesterol from the blood, leading to lower LDL-C levels. This direct action on bile acids distinguishes it from drugs that directly inhibit cholesterol synthesis and from those that reduce fat absorption; the rise in LDL receptor activity is a downstream effect, not the initiating step.