Hormesis, definition

Hormesis is the term used for the phenomenon of stimulatory effects at low-level exposure, and inhibition at high-level exposure. The term derives from the Greek word Hormo which means excite or set in motion, and which is also the root of the word hormone. The concept of hormesis dates back to the 1920s. A substance showing hormesis has the opposite effect in small doses compared to effects at large doses. The definition of hormesis does not imply that low-dose effects are necessarily beneficial, only that they are opposite to high-dose effects. 

---