Years back I had a friend who used to take a little bit of GBL and hit the gym. I was never experienced and tolerated enough to do the same but he swore it was good, helped him push a bit harder, and also said made him hungry which is good after gym if you're looking to bulk.
He'd also knock himself out on it most nights and swore he used to grow bigger faster, due to the anabolic sleep state it forces you into.
He was of course a massive drug addict so possibly delusions. But we did some research, aparantly mixing it with some Bulgarian medicine called BROMOCRYPTINE or BROMOCRIPTINE would have a great effect on growth. I planned to use the combo combined with test in a 12 week cycle once but never got round to it.
There is a thread on here somewhere about it I'll see if I can find it