I once part timed at GNC. We got 4 bucks commission for selling that shit (endothil) and hyping it up. I used to make around 14 bucks an hour hustling garbage.
So what does work?
_Creatine, taurine, multivitamins, some solid source of omega 3 and you're good to go, don't waste your time with anything else imo, and DO NOT buy it at GNC, rip off city.