Mia...Welcome to the boards! The only difference is the amount of APAP (APAP is Tylenol), and one has 325mg of APAP (Tylenol), and the other has 500mg of APAP. Neither one is without the APAP/Tylenol. So, one has 175mg more Tylenol than the other. No other difference. The 7.5/325 is the generic for Norco, and the 7.5/500 is generic Lortab.