I had percocets for when my wisdom teeth were out and they did nothing for me. I stopped taking them and felt exactly the same, as well as with the pain.
percocet is a mix of acetominaphine (sp?) and oxycodone - I had heard that the opiate doesn't really alleviate the pain but detatches any personal reference from it, so that you don't care that you have it - depersonalization of the pain.
the acetominphine actually works against the pain via blocking the proglastins.
no matter how much I took, I never felt anything good or bad from them either way and was certainly never addicted - but I only used them for a short while after surgery and was in really bad pain.
as for it being synthetic, I don't recall reading anything about that when I had them.
here at work we have a PDR system two cubes over from me, I could look in there I suppose.