He had twice gone into rehab already.
Was he still having back pain? Did the doctor say, "you aren't positively responding to the medication anymore" or "you are building up a tolerance to the medication and eventually will get hooked" and stop writing prescriptions? Or did the doctor continue writing low dosage prescriptions which Rush exceeded (and needed an additional source for)?
Was the addiction mental or physical? Did he have cold sweats without it and nervous disorders or did he have muscle spasms and sharp pains?
Some on FR seem to be of the mind that he was just getting off on getting dosed by an opiate. This does not seem to be the case.