Statins reduce circulating LDL cholesterol by inhibiting HMG-CoA reductase, a key enzyme in hepatic cholesterol synthesis.

Study: 2013 Cholesterol Guidelines Revisited: Percent LDL Cholesterol Reduction or Attained LDL Cholesterol Level or Both for Prognosis?

This study shows that when people take statins, their 'bad' cholesterol (LDL) goes down, and the more it drops, the fewer heart attacks and strokes they have. This supports the idea that statins work by lowering LDL cholesterol in the blood.

Study: The effects of lowering LDL cholesterol with statin therapy in people at low risk of vascular disease: meta-analysis of individual data from 27 randomised trials

This study shows that taking statins lowers bad cholesterol in the blood, which is exactly what the claim says. It didn't test the enzyme directly, but it proved statins work the way we think they do — by reducing LDL cholesterol.

Study: LDL Cholesterol Reduction Variability with Different Types and Doses of Statins in Monotherapy or Combined with Ezetimibe. Results from the Spanish Arteriosclerosis Society Dyslipidaemia Registry

This study shows that statin drugs lower bad cholesterol in the blood, and since all statins work by blocking the same liver enzyme (HMG-CoA reductase), it proves that blocking this enzyme really does reduce cholesterol.

Study: Pleiotropic effects of statins: benefit beyond cholesterol reduction? A meta-regression analysis.

Statins lower bad cholesterol in the blood, and this study shows that’s exactly how they help prevent heart disease — no other secret tricks. So yes, they work by blocking a liver enzyme that makes cholesterol.