40 mg is not high, it's the norm. Dosage of Simvastatin ca be as high as 80 mg. I am curious why you are on a statin with a total cholesterol of 160. What s your breakdown by LDL & HDL and do you have any risk factors of CAD currently? Plus, if your script was for 20 mg I would question the pharmacy about receiving 40 mg.
Let us know when you can and we can speak more accurately about your dosage.
Jon
Combine it with niacin, and you'll reduce your risk by more than 50%.