GPCRs sit at the center of modern pharmacology. Close to a third of all approved medicines work by switching these proteins on or off, yet a lot of students, and more than a few practicing clinicians, only ever meet them as a maze of numbered subtypes. This guide covers what GPCRs are, how they are built, how the field organizes them into families, and why they stay the most productive hunting ground in drug discovery. What is a G protein-coupled receptor? A G protein-coupled receptor, usually shortened to GPCR and sometimes called a 7TM receptor, is a membrane protein that sits in the outer envelope of a cell and passes…