My mother used to say that she had no relief from any analgesia. At the time I didn't really believe her, but now I certainly do! It's very likely that she - and I - were poor metabolisers of drugs metabolised by the CYP4 pathways, which would also account for excessive reactions to drugs which are metabolised more slowly than normal. This problem would mean that drugs needing to be broken down in this way, such as codeine, have less or no effect. However, I would have expected buprenorphine or Oramorph to work - which they don't. I also have little relief from most antidepressants - doing better on the older tricyclic medications.
I really find TENS to be the only effective pain relief - apart from the radiofrequency ablation for my low back pain. However, nothing is working for what is presumed to be polymyalgia rheumatica pain/ and I think my steroids will have to go up quite a lot again.