Well, sir, Zydrate was created by GenCo to relieve surgery pains. Seeing as how there was a large epidemic of organ failure, surgery was needed to save lives. Though, most people perished until Largo made his way to the top.
Eventually, he was able to save lives with all of the organs he obtained. But it wasn't a cheap business, and well... Organ reposession became legalized. Getting new body parts became more of a fashion statement than anything else, and Zydrate became one of the top selling painkillers.
Not exactly sure what's in it, but I have my sources. Pure glow, ready to be inserted into the gun, and injected into the body. Works instantly, and numbs the pain for hours.