What makes a GPCR agonist an agonist and antagonist an antagonist?

“Prediction of ligand-receptor pharmacological activities using a combined docking and machine learning approach” by Mireia Jimenez-Roses et al.

AI-based one-line summary “Ligands exert their action on GPCRs via the interactions they make in the ligand binding pocket that mediate their action.”

https://www.biorxiv.org/content/10.1101/2021.03.18.434755v1