Atorvastatin is a moderate-high intensity statin while Simvastatin is a low-moderate intensity statin. This means that Atorvastatin can result in significantly greater reductions in LDL levels at lower dosages compared to Simvastatin.
Atorvastatin is long-acting, it stays in the body longer than Simvastatin. Atorvastatin can be taken any time of the day, however, it is preferable to take Simvastatin in the evening for best results.
In terms of safety, there are no significant differences in the side effect profiles. Both Atorvastatin and Simvastatin may interact with other medications and food. Always inform a pharmacist or your doctor about all medications, supplements or health products you are taking.