Final answer:
An agonist is a drug that produces the same type of response as the endogenous substance, while an antagonist is a drug that prevents the endogenous chemical from acting.
Step-by-step explanation:
An agonist is a drug that produces the same type of response as the endogenous substance, while an antagonist is a drug that prevents the endogenous chemical from acting.
For example, if a neurotransmitter is low in the brain and an agonist is administered, it will bind to the receptor and produce the same effect as the endogenous neurotransmitter. On the other hand, if an antagonist is administered, it will bind to the receptor and block the endogenous neurotransmitter from acting.