Looking at the ingredients of N-Large there are an awful lot of aminos in there - not all of them 'essential'. I can't take non-essential amino acids they make me feel terribly sick and dizzy and a few years ago after taking an amino packed protein formula - I completely passed out at the gym!! - but I'm not allergic or intolerant to any proteins when taken in normal food.
I'm no food scientist but I expect it's because some of the non-essential amino acids are already in your blood when you take the mixture and generally when there are an excess of non-essential amino acids in the blood, the body turns them back into their former essential amino form... If you take a load of non-essential proteins all at once, the body is working frantically hard to re-address the balance and frankly, can't cope! Try getting a mixture that only contains the ESSENTIAL amino acids with particular emphasis on the branch chain ones (leucine, isoleucine, and valine) - these three are supposed to make up 70% of our total protein uptake and are known to be particularly active in the muscle recovery process after exercise.
My advice is, if you need a supplement, only take one containing the essential aminos - after that, let your body be the one to guage what quantity of the non-essential aminos you need
