Its an amino acid which is a "building block" for protein. I use to take it daily but i did a post asking which OTC supps everyone takes and i think i was the only one takin it. I always thought Protein/Glutamine cqme hand in hand but ppl were saying its overrated. So i honestly cant tell u exactly.
Its not something Ive taken and noticed anything from. Regular glutamine has poor absorption and you will need to take alot of it. Look for glutamine peptides, they have better absorption, but taste horrible and mix poorly.
its a good supplement to take, I take it in my pre/intra/post workout shake along with other amino's as well. It's good for retaining muscle when dieting just like bcaa's
I use it for colds. When I feel one coming on I'll mega-dose it (usually 30g at a time, 2-3X daily) and I'll either not get the cold or it'll only last a day or so.