An agonist is a ligand (molecules that bind other molecules) that can be a drug or an endogenous molecule that bind to a receptor and elicit a cellular response, usually a signalling pathway. An example of an endogenous molecule that would be an agonist could be a neurotransmitter or a hormone, such as estradiol  .
Another example of an agonist is nicotine. Nicotine is a natural compound and is the chemical that is found in tobacco. Nicotine acts as an antagonist by binding to the same receptor as the main excitatory neurotransmitter acetylcholine and mimics the action of this neurotransmitter, therefore eliciting a cellular response .
Partial agonist is a compound that binds to a receptor producing an incomplete response, therefore it is considered to be less potent.
The opposite of an agonist is an antagonist.
- ↑ Berg et al., (2006) Biochemistry, 6th edition, New York, Pg 910
- ↑ Silverthorn et al., (2009) Human Physiology: An Integrated Approach, 5th Edition, San Francisco, Pg 41