As ARIZONA said, the changing of 20 mg. Lipitor for the 80 mg. Zocor really is the equivalent of going from 20 to 40 mg. Lipitor. Did your doctor make the change because you were doing poorly on the Lipitor.
I would ask him point blank: "Why did you make this change?" His answer might prove enlightening, especially if it begins with a stammer.
Some people have the change made by an insurance company because they struck a better price deal, but your doctor SHOULD NEVER be motivated by such mundane things as MONEY?
<Oh, I HOPE I don't stick my tongue clear through my cheek!