After a drug is administered, it undergoes the process of
absorption
metabolism
excretion

it's metabolism
Metabolism is a term that is used to describe all chemical reactions involved in maintaining the living state of the cells and the organism. Metabolism can be conveniently divided into two categories: Catabolism - the breakdown of molecules to obtain energy.

absorption
In chemistry, absorption is a physical or chemical phenomenon or a process in which atoms, molecules or ions enter some bulk phase – gas, liquid or solid material.

excretion(in living organisms and cells) the process of eliminating or expelling waste matter.a product excreted by a living organism or cell.plural noun: excretions"bodily excretions"

Stimulants speed up the central nervous system.

Answerfact;