For me, GABA felt like a small dose of a benzo. At high doses it would give this sort of flushed/burning feeling which kept me from increasing the dose further. I think I read that it can effect insulin levels, but I can't remember how. I didn't take it for too long, so I don't know about any long term effects.
The lessened anxiety was nice, but a pretty small effect for me. Hopefully, YMMV.