I was a non-science major and felt like I was playing catch up with the biochemistry and cell-biology majors but after 1st year everyone was essentially at the same level.
People say don't pre-study. I say... why not? Repetition is the only way you learn in medical school unless you have an eidetic memory or are a genius. If you read BRS Physiology once, none of it will stick... but it will stick better the second time through during first year. It might be seen as a waste of time, but at the end of the day you're the arbiter of how you waste your time.
I'm in my 4th year and should be relaxing and vacationing. Instead, I waste my time by reading The ICU Book and Mastery of Surgery (should probably buy Sabiston), because I like to read about this stuff.