More info on niacin/tryptophan https://www.youtube.com/watch?v=yofewUE6L-k https://www.youtube.com/watch?v=-l0S25DIxqw
I took niacin once in pill form and it made my body burst out into a fierce itch rash that lasted about an hour.
I haven't used it in forever but when I did sort of just got accustomed to being itchy until it wore off. I've read that it can cause liver issues, though. I just quit taking pwo's altogether.