agonist

https://doi.org/10.1351/goldbook.A00186
Substance which binds to cell receptors normally responding to naturally occurring substances and which produces a response of its own.
See also:
antagonist
Source:
PAC, 1993, 65, 2003. (Glossary for chemists of terms used in toxicology (IUPAC Recommendations 1993)) on page 2011 [Terms] [Paper]