It's an essence extracted from someone's skull at the point of death.
It's highly euphoric and addictive. You don't feel anything while it's inside of you.
Amber Sweet (Paris Hilton) is addicted to it in Repo! The Genetic Opera. She has a sexual relationship with G-Rob who she gets it from.
It's generally used before getting surgery.
Though, it's highly abused.
(From Zydrate Anatomy)
Zydrate comes in a little glass vial.
A little glass vial?
A little glass vial!
And the little glass vial goes into the gun like battery.
And the Zydrate gun goes somewhere against your anatomy
And when the gun goes off, it sparks and you're ready for surgery.