I'm not quite sure where that exact wording comes from; perhaps a quote from Ostler's Web : The Canadian criteria also include : I'm not sure how common this is but it does apply to me. Two anecdotes. When I was working I was having major problems with heat intolerance/overheating and my GP thought (reasonably) that the problem may have been due to the sympathetic nervous system and prescribed a beta blocker (propranolol - standard dose. It worked - in spades. I ended up absolutely freezing and completely knocked off my feet to the degree that I couldn't function at all. I stopped taking them as there was no way I'd make it into work. On another occasion I scrounged a painkiller (Kapake - codeine) from my wife (who has degenerative disc disease and a so has a pharmacopoeia on hand). At time she would be on up to 8 Kapake a day and able to function pretty pain free. After a single tablet I giggled uncontrollably for 30 minutes then fell asleep for 12 hours Anyway - I often wonder if some of these odd symptoms might hint at where the central problem lies. I can only think of two explanations for this oversensitivity. (a) meds cause a disproportionate physiological reaction in PWME perhaps due to some breakdown in 'control mechanisms'/feedback loops; (b) the physiological response to meds is normal and proportional but the perception of expected minor physiological changes is disproportionate. I would have thought that (a) would be fairly easy to test?