I have used tramadol for chronic back issues and have found it helps ME symptoms as well, especialyy when i first used it, it helped with energy and mental clarity etc, it still does now but not to the same degree. I think some of its positive effects are not just from opiod receptors but tramadol also affects serotonin and noradrenaline, and maybe it does this in some unique way as i and others seem to tolerate it well compared to some ad's that also work on similar receptors?? But tramadol is one of those meds that people either like or dislike due to sied effects. I did use a slow release morphine for a couple of months for my back and i found it not as useful as tramadol??