What happens if a person takes more percocet than prescribed? i found out my fiance just took 2.5 pills at once instead of 1 every 8 hrs

Depends . . .: Check out https://online.Epocrates.Com/noframe/showpage.Do?Method=drugs&monographid=2297 (you might need to register for free) & http://www.Drugs.Com/percocet.Html for info on percocet. It's narcotic that, in worse case scenario, can be addictive, stop breathing, and cause confusion & severe constipation if taken for long periods of time at high enough doses especially if not "used to" high dose.