Gamma Hydroxybutyrate (GHB) is a wicked sedative. I'm not exactly sure how to quantify it, but I would say from personal experince and my limited knowledge of pharmacology, that you're dealing with something in the vein of Alcohol, Barbiturates, Benzoiazepines et al. It packs a mean punch if you combine it with any other sedative in this family. I've only had a handful experiences, but each time it left me drooling.
I wouldn't use it alone. I'm not really sure what formulation you're working with, but it's safe to assume it's clandestinely made solution? You will probably have some kind of idea of relative potency, but it's a liquid and by definition its potency is dubious. Just as if you were using Opioids, the wise thing is to start small, analyze the effects and increase stepwise until you are where you want to be. Just take it slow.
As always, I'll leave the calling card for Never Use Alone. It's pretty cool. You call them before you use if you're worried about overdosing. They can then attempt to call you after several minutes and if you don't respond, they will automatically dispatch first responders. There's no reason not to use this service outside of the potential for embarrassment. It's your life after all. Here is the number.
(800) 484-3731
God bless these guys. We are losing too many of our people to preventable tragedies.