Something's Rotten in Faerun
Potion of Longevity
The longevity potion reduces the character’s age by 1d12 years, restoring youth and vigor. The entire potion must be consumed to achieve the desired result. It is also useful as a counter to magical or monster-based aging attacks.
Each time one drinks a longevity potion, there is a 1% cumulative chance the effect will be the reverse of what the consumer wants—all age removed by previous drinks will be restored!