First, you can just be purely allergic to the opiates you mentioned. My friend is so allergic to the codiene class, which includes vics percs, roxis and oxys and so on, that they had to start her on dialudid for pain, which is the morphone class of opiates. When I first started chewing oxys I nearly clawed holes in my skin from scratching so badly, and the nausea. And realized shit, I should be eating 40's off the bat, I went back to where it all began for me, when vicoden hit me like my first shot of persian gold, and then slowly worked my way up through vic doses, then percs, then roxis, then oxys, then before I knew it H was my best friend along with fentanyl.
Opiate receptors are a part of our chemical make up, so the body will eventually respond in kind to what you give it as long as you treat it with respect, and give it the time it needs to adapt, hell after yrs of using pharms, I thought smack would be a breeze, 1minute into that first shot, it was projectile vomit, having to sit to piss cause I got tired from standing so long waiting for it to come out, and being constipated, all the realities of opiate use. Now, even though Im on genuine pain management, I still need 2 docs, each giving me 180 30mg roxis a month, plus Opana