I know this is resurrecting this thread, but I thought for the sake of future searches by other people I could contribute..
I'm on a high dose of sub(4-12mg a day) and have been for a month..before hand, I was on high dose morphine for four years..
Since switching over, I wake up every morning with raging wood..I can get it up no prob, and actually have to pull out a lot to keep from being a minute man..
So, compared to a pure nu agonist, bupe has caused my test to soar..
It also prob should be said that I lift weights frequently (five times a week)..heavy weight(8rep max), moderate volume(prob 24 total sets of varied exercises), total body(don't neglect legs back etc.)
I also eat lots and try and get 100grams of protein a day, and eight hours of sleep a night..take a multi every couple days..
So if you're on bupe and experiencing ED, you may want to consider the gym and diet as the best bet to getting your test on the right track before you go the AAS route.