Hi
@Hd-x - I think I reacted so strongly to the glycine because of its role in detoxification. Here's one article which mentions glycine (among several other things) and phase II liver detoxification:
https://www.diagnose-me.com/treatment/liver-detoxification-phase-II-support.php
If you google glycine and detoxification, you'll find a lot of information. Anything that had said it had cleansing properties like apple cider vinegar, made me detox unpleasantly, but it was never resolved. It just kept happening over and over and I believe the toxins were just being released from the cells and circulating and then resettling - not being excreted from my body. With the glycine I stuck with it, very small doses at first (after the first large one) and just gradually increased it. I don't know exactly how much the small dose was I settled on, possibly as low as 100 mg. I'm now taking 2000 mg before bed and 2000 mg more middle of the night before sleep with no problem, and I almost never have detox symptoms any more.
Actually the first thing I took with glycine was gelatin, which is high in glycine, and that's what hit me like a truck. Then I switched to pure glycine and had to be very careful with it. It hit me very hard, but no longer does.
Glutamine helped some too (mentioned in above article) but I eventually had to stop it because it was causing sleep problems unfortunately.