Atorvastatin and simvastatin are both selective inhibitors of HMG-CoA reductase, which can lower plasma levels of cholesterol and lipoproteins, thus treating hypercholesterolemia, mixed cholesterolemia, and primary and secondary prevention of atherosclerotic diseases. The difference is that simvastatin is an earlier product and atorvastatin is a more recent product, and atorvastatin is a stronger lipid-lowering agent than simvastatin. Atorvastatin has fewer adverse effects than simvastatin, mainly in terms of damage to the transverse muscles and damage to the liver. Atorvastatin has fewer side effects than simvastatin, and current guidelines recommend newer lipid-regulating drugs such as atorvastatin.