Elixir of Life

Elixir of Life is a product of the Sacred Flame, utilised by the Sisterhood of Karn to give them extended life.

It can also be used to restore a person/Time Lord after a dangerous battle. (DW: The Brain of Morbius)

It is most likely a key ingredient in Sisterhood Salve.

It is produced on Karn via the Sacred Flame and the rocks in which the flame is housed, a goblet is placed below the flame producing the Elixir. This may be a remanent of the Pythia's 'magic'.