It might not be a bad idea, depending on a couple of factors...
What is your academic background? What type of medical school curriculum are you entering? How comfortable do you feel with biological principles?
Some schools do a really great job of building a foundation and presenting the material in a well-organized, comprehensive manner. Some schools don't.
For example, my school uses a completely integrated curriculum (meaning anatomy, biochem, pharm, physio, embryo, histo) are taught all at the same time through the lens of an organ system. The curriculum is almost entirely new (within a year of implementation). And, just to lay all of the cards on the table, the implementation has not been without its very rough parts.
In order to understand ANY of the information presented, I found it pretty critical to have a strong foundation in subjects like cellular bio, transport, membrane potentials, biochem, et cetera, and be able to recognize its application. I found that this was really not built in a very straightforward manner (this is a pretty common problem with integrated curricula). Since physio builds on cell bio/biochem (some histo), anatomy builds on embryo, pharm builds on physio, I found that not having a strong foundation in these subjects, well, caused me to be a bit lost. This can lead to stress and some pretty tense exams.
What I wish I had done: I wish I had found Costanzo's Physiology text beforehand and read between my acceptance and start date (it's about 300 pages). She does a good job of building base knowledge and applying it. Her writing is very clear and well illustrated. Also, brushing up on some biochem would help (personally never having taken it in undergrad).
Studying ahead does not make you a gunner. It just makes you someone who wants to do well in class (and hopefully avoid the misery of academic struggles).
