Do you mean a research post bacc or premed coursework?
Is your sGPA low? MCAT good? Decent ECs?
Did you do poorly on or not take all of the required science courses?
Those are the first questions that come to my mind as to why someone would need to improve their stats with a post bacc and I would need at least those answered before I could enthusiastically say one or the other.
I can definitely say this though: only apply once you're 100% ready with your best application possible.
More reading here:
Is a Post-Bacc Program Right for Me? Seven Benefits to Consider