Shocked to not see this listed here, although maybe I'm just missing something obvious. This is a unique compound and I got a lot of out it. It kept me off of heroin for about six months, and I felt great on moderate-high doses of it. Sadly, there is a nasty withdrawal from it, hard to explain and it is like part opiate detox and part head fuck. I remember I was in the ER for something unrelated and I had run out of it and was kicking. They were giving me morphine for my unrelated injury and it wasn't even touching the withdrawal.
Still, I was very productive on it and it helped a ton with focus and concentration. High doses had that speedy "oxycontin" type rush people like to muse about from back when OC80s were plentiful. Anyway, check it out.