ELI5: How did drugs originate?

Since I was old enough to comprehend what drugs were, and where they came from, I've always wondered one thing: how did they originate? For example, who thought smoking the buds of the cannabis plant would be a good idea? How was the chemical formula for meth created? Who decided it would be a good idea to refine poppy plant into morphine, and refine morphine into heroin? How was it discovered that cocaine could be extracted from the leaves of the coca plant with different chemicals, etc.