Be very careful.
My first time using opana I picked up a 40. My oxy tolerance was about 30mgs snorted at that time. All my friends were using it, so I decided at that time to give it a try even tho I am a big Oxy Fan. Anyway I first ground out around 3-4 mgs the first time, wait about 10min for it to hit me and I didn't really feel anything. So I figured fuck it and I ground it down so I had 3/4 left. So I snorted 10mgs total. 5min later I got hit like a ton of bricks, in and out sleeping, I couldn't stand up, I couldn't even open my water bottle. I started to puke, which I think helped me sort of lose the high. My friends made me stay awake, they had to keep slapping me. So I got REALLY lucky, if people were not around I probably would have died.