An Elixir brought into existence by a Port. Drinking this will add several years to your life, and heal any wounds you have received. Also drinking this will increase your bodies healing capabilities for a while after. The Elixir will never run out.
The Elixir of Life was brought into this universe by a Port name Derek(Creator of the Nether Case and Nether Key). He sealed a dimension, which was filled with an endless supply of the fluid that has the life giving abilities, into an unbreakable vial outside of this dimension.
Drinking this too much in a single serving or for too long will cause several health problems. The most common being paranoia and multiple personality syndrome.