Alternative medicine is any practice that is put forward as having the healing effects of medicine, but does not originate from evidence gathered using the scientific method. So e.g. candling, homeopathy, Whole Body Vibration Training, acupuncture, etc. Given that either the effect sizes of these methods are negligible or they don't work at all, these practices are irrational from both the epistemic and the instrumental perspective. The explanation of the assertion might be a bit circular since any "alternative" medicine that works would simply be medicine. Well I can't do anything about that.