Spectrox

Spectrox is a substance harvested on the planet Androzani Minor. It is naturally found (in dense, white, fibrous clusters) in the chrysalis of the Spectrox Bat, a species that lives in the many caves that riddle the dry desert planet.

Unrefined spectrox is a powerful neurotoxin, capable of killing even a Time Lord. (See Spectrox toxaemia.) Refined spectrox, taken in regular doses, can prolong a human lifespan to about twice its ordinary length, greatly slowing the aging process. Because it is so dangerous in its raw form, it is harvested by androids and brought to special refineries. After this, the spectrox is shipped to Androzani Major and then the rest of the galaxy.

Refined spectrox needs to be taken daily, though aging will only continue after a week or so. Because of its uses and rarity, spectrox is one of the most valued substances in the galaxy and many battles--both covert and overt--were fought over its possession and distribution. (DW: The Caves of Androzani)