I felt the irritation someone complained about! I was taking like 4 scoops a day, though. My mother noticed it first. She said I was answering back sharply. I cycle now. I think Level1J or someone mentioned cycling as a better option than taking it daily at max dose. I agree now.
Still, once I take it after not taking it for a few days I feel alert, focused, cheerful. If I take it a lot, I grow tolerant or something because it doesn't feel the same when I take sarcosine after not taking it the day before.
Also, I think if you mix alcohol with sarcosine on accident, the sarcosine levels spike and you might get ultra irritable. Yes, I know it's a bad idea to mix sarcosine and alcohol, I just wanted to put this info out there before others do what I did