The Adarnian were a alien species that existed in the 30th Millennium.
Adarnians biology contained regenerative qualities that made them a target of humanity's genocide. However there were three draw backs from using the Adarnian's genetic material. The first was the intense pain the elixir caused its users. The second and third were more detrimental as the youth brought about by the elixir was only temporary and afterwards left the user's body in an even more decrepit state.
The Adarnian were discovered by the Imperium, during the Great Crusade. In a rare example of the Imperium's mercy, the Adarnians were spare from extermination as the aliens were deemed harmless and given protectorate status. However it was soon discovered that the Adarnians genetic makeup possessed miraculous restorative effects on Humans.
When the Adarnian's bodies were rendered down to a fluid, it created an elixir, that when injected into the bloodstream could reverse aging well better that the standard Imperium's Rejuvenat treatments. The Adarnians were soon harvested to extinction.
Currently, the elixir has not been available for ten millennia, since the Adarnians extinction and no one was able to synthesize the species' genetic material.
- Belisarius Cawl: The Great Work by Guy Haley