Deciding to begin serious pain relief with opiates I believe requires some thought.

It has been learned very recently that the glial cells that support the brain neurons, will detect that the pain receptors in the brain are "filled" with opiate, so they direct those cells to make MORE receptors. This then registers more pain... and that is when doses, must be raised. It is one form of tolerance. So that if a person decides to wean off opiates for some reason, they don't go back to what they WERE, but to a new level, with MORE pain receptors.

This is the body's way of keeping some pain tracts open, because perception of pain, is an evolutionary advantage, to protect the body from further harm.

Here is but one article to explain this process:
http://nervepainhelp.com/neuropathy-opiate-drugs/