Across the world, we consume approximately 100 million kilograms of caffeine each year. This puts it at the top of the list for the worlds most widely consumed psychoactive drug. Caffeine is consumed through various supplements, medications, and foods. But, the most notable method of consumption, is of course, coffee. It seems strange to call coffee a psychoactive, but any chemical substance that changes our mental state by affecting our brain and nervous system, is a psychoactive by definition.
To understand how caffeine affects us, our brain, and our nervous system, we first need some context about how our brain works. Among other things, your brain is made up of lots of different types of receptors. You can think of them as tiny docking stations for your brain, places where it can receive and process various different chemicals. By design, receptors aren't one-size fits all, they're structured to allow the processing of the particular chemicals that they're responsible for.