"opana er is the 1st er medication that i&#039;ve tried that actually works for an extended period of time. and i&#039;ve had to try many for my severe back and neck injuries. one 20mg pill will last at least 8 hrs, and i work long 16 hr days so that&#039;s a very good thing. i highly recommend it for people with severe problems/injuries. i definitely wouldn&#039;t recommend it for just mild to moderate pain problems or acute problems. most ideal for people with chronic severe injuries who also work a lot."