I have usually eat about 1.5X the amount I would with instant relase oxy but it takes longer to come on but it last forever. I got a tolerance if like 50 mgs of roxi so I'll take 80 mgs if the OP or so and I'm good. Worst comes to worse just take a little and work your way up.
You can get high but you can't get unhigh, so keep that in mind. Good luck