Answer:
Agonist drug is a drug that produces intended effect similar to the intended chemical and receptor. Example, endorphins are natural agonist drugs and heroin is an artificial agonist drug that turns to morphine in the body and gets attached to the opiod receptors in the brain and released to the pathways with dopamine.
Antagonist drug is a drug that stops the receptor to produce a response. Example, naloxone that is used to counteract a drug overdose from opiod.
This is what I think. All the best!
