A highly dangerous and radioactive drug, Xenite is not native to the world of Top Ten (and America’s Best Comics in general). It is an element from a different periodic table, specifically that of Grand Central, the parallel universe of Precinct 1.
Given its nature, there are very few people who can use it without suffering radiation poisoning, all of them superhuman or divine in nature. The only known user of the drug at this time is Commisioner Ultima, of Grand Central, whose power levels were akin to those of Superman. As she is now deceased, the origins and history of the drug may never be known.
In effect, the drug appeared to be a form of super-powered heroin, although given that the only depiction of its use was a deliberate overdose, it is hard to be certain of this identification.