The HMG-CoA Reductase enzyme causes the body to make more cholesterol. If it is inhibited, the body makes "less" cholesterol. So statin drugs lower the amount of LDL (bad) cholesterol in the blood which stops atherosclerosis from getting worse. Statin drugs can even help make atherosclerosis better. However, statins are not as good at increasing the HDL (good) cholesterol. Low HDL is hard to treat with medicines, but goes up with more exercise.