in theory when you look at each individual compound most would think gh is the culprit due to its ability to cause growth in everything.
i have often wondered if the reason for the guts was continued use of gh year round. As i know many top pro's are using high dosages of gh ( and slin) while taking a break from gear to keep their mass, then they add the gear back when preping for a show and grow into it. i originally thought that the constant gh year round caused the guts. however the biggest abusers of gh in the world are probably proffesional athletes - specifically from the nfl, nba, mlb and olympians, and they have no guts ( bodybuilders sized guts that is).
the only new compounds from 95 onwards were insulin, then igf-1, and later pgf etc. thats when they started showing up.
gh does have ugly sides for definate though i.e. bone growth - as you can see from cutlers jaw, cormiers skull, ronnies skull, dexters skull, etc