I have an old script for prednisone 20mg date filled was 06/20/2014 it is now 9/13/17 is it safe?

Hi C711,
I would say most likely, yes it's okay to take. If it's been kept in a controlled temperature, with low humidity (in other words, not in the car or bathroom) it should be alright. If they smell different or have started to lose their coating, change color or have begun to disintegrate, pitch them. The main drugs I don't use much beyond expiry are liquid suspensions, especially oral anti fungals, and antibiotics. There are probably others, but if I haven't taken them, I am unfamiliar with their shelf life. Hope that this helped.