Elixir of Life

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

It could also be used to heal serious injuries. Time Lords occasionally used it when undergoing a difficult regeneration. It was used by the Sisterhood to heal the Doctor after his Mindbending battle with Morbius (DW: The Brain of Morbius)

The Elixir was produced on Karn as water from underground springs passed through the rocks heated by the Sacred Flame directly below them. The rocks contained numerous rare minerals and compounds which were released into the water when heated. A goblet was placed below the flame to catch the Elixir.

It is most likely a key ingredient in Sisterhood Salve.