stimulant

1. (pharmacology) A substance that acts to increase physiological or nervous activity in the body.Examples: "Milk of chameleon was recommended as an erotic stimulant by Avicenna."; "“Uppers” are what’s known as stimulants while “downers” are what is classified as depressants. […] Uppers increased cardiovascular and respiratory functions to dangerous degrees that can overwhelm the body. If you’ve ever felt an adrenaline rush before, you likely felt shaky, weak, or dizzy once it passed. This is similar to what stimulant drug users experience once a stimulant wears off. Feelings of exhaustion and depression set in and users seek more uppers to ward off what’s known as a “crash”."