Just to add to the discussion, opiates do not and have never had substantial effect on me. I've never had chronic pain issues, but on maybe half a dozen occasions in my life have been prescibed opiates for temporarily severe problems - a bad root canal, hopsitalized for migraine, a temporary back injury, stuff like that. They had no more effect on me than, say, a couple of Advils.
Conversely, my father, if he takes something like that, can barely stand up thirty minutes later. Go figure.