Agonist has a number of meanings
- Agonist, a substance that binds to a receptor to induce a biochemical response
- Inverse agonist, a substance that induces the opposite effect of an agonist
- A person or animal engaged in a struggle - see agonistic behaviour
- A muscle that contracts and operates in opposition to another - see agonist (muscle), a muscle type
- An advocate of the political theory of agonism (or 'agonistic pluralism').