Chemist/Fallout: New Vegas

Chemist is a perk in Fallout 3, Fallout: New Vegas, and Fallout 4.

Fallout 3 and Fallout: New Vegas
All chems (including alcoholic beverages) affect the player for twice as long with the Chemist perk. Any substance that influences the 'Chems Taken' statistic in the Pip-Boy 3000 is affected.

Fallout 4
With each rank of this perk, the duration of a chem's effects are increases by 50%. Rank 1 raises it by 50%, Rank 2 doubles the duration, Rank 3 increases the duration 150%, and Rank 4 triples the duration of the chem.

Bugs

 * In Fallout: New Vegas, any item that has an effect that lasts for a given period of time (for example, the AP bonus from Jet, the skill point bonus from skill magazines, the health restored from food, et cetera) has its effective duration doubled. Notably, even items that have negative effects, such as Fixer's blurry addiction withdrawal, show an increased duration. Essentially, Chemist affects every consumable beyond skill books and stimpaks in casual mode.