As far as I know it is an amino acid that enhances brain activity and can reduce appetite – so it is used for the likes of depression to stimulate brain and sometimes as appetite supressant. i think it sort of tricks the brain into thinking there is less pain than there is by sort of changing the perception of the pain so can be used for pain control but am not too sure.
I dont know of it being used in dogs but you have sparked an interest now so am off to do some research.
You can get it from the likes of Holland and Barratt but dont go do anything with it until you know all the answers to the questions you have.