Fast Metabolism (Fallout 3)

Fast Metabolism is a perk in Fallout 3 and Fallout: New Vegas

Fallout 3 and Fallout: New Vegas
With the Fast Metabolism perk, the player character gains a 20% bonus when using stimpaks. In Hardcore mode, the multiplier increases the amount of healing per second making stimpaks an even better in-combat healing option. Players outside of Hardcore mode may be better served by simply applying multiple stimpaks from their Pip-Boy rather than investing in the perk.

This perk also affects (adapted) alien biogel, which is added to Fallout 3 with the Mothership Zeta add-on.