The longevity potion reduces the character’s game age by from 1-12 years when it is imbibed, but each time one is drunk there is a 1% cumulative chance that it will have the effect of reversing all age removal from previously consumed longevity potions. 

The potion otherwise restores youth and vigor. It is also useful to counter magical or monster-based aging attacks. 

The entire potion must be consumed to achieve the results.