This key amino acid is a "double edged sword." Although it may help raise growth hormone, which would be beneficial in most CFS/FMS patients, it also can raise nitric oxide (which is postulated by Professor Martin Pall to be too high in CFS—for more on his theories see the web site notes). Interestingly, B12 shots act as powerful nitric oxide scavengers, and this may be another reason they are so helpful—even in those with normal B12 blood levels. My main concern with arginine is that it promotes the growth of some viruses in the herpes family, and therefore may also stimulate HHV-6 and Epstein Barr Viral growth. Therefore I recommend that only low levels be used in supplements for CFS/FMS.