(((Ivan))) I don't really know the reason, but I do know (from reading here) that opiates have a tendency to make pain worse, and you need more, more, more. I'm sure there's a medical reason, and I've just forgotten it from my years of being a nurse. I trust the people here, though, and I have no doubt that using opiates makes things worse, and your dependence go up.
Hugs and prayers,
Amy