I started taking arginine as part of a small amino stack to counter the rapid muscle wasting I am experiencing. It's really good at opening up blood vessels - it sounds silly but I can tell because it quiets the tinnitus. Yet it exacerbates my POTS problem. I often feel very moody and anxious after I have been on my feet for a while and this effect is tripled on arginine. I thought this was a PEM type thing but I realized it was due to poor circulation to the brain as it resolves rather fast on lying down. Also, I saw this ... OK I can't find the specific link now ... but basically continuous use of arginine could cause oxidative stress due to its influence on nitric oxide. And I wonder, as I do with so many supplements, am I doing more long term damage to myself by trying this?