The more I think about it the more I wonder. While eating is a necessary and instinctual thing to do, smoking is absolutely not. Ingesting plants/meat orally can sometimes give you different highs or have a strong effect on the body/mind, but smoking them would take a whole new level of creativity. When and how did humans learn to not only smoke plants but then specifically grow and harvest particularly-powerful plants (opium, cannabis, tobacco, coca plant) for use? Also is there any hard evidence of documented substance abuse/addiction in ancient cultures, and if so what were the repercussions for someone who became physically dependent/addicted to such things? Is there any documented evidence of withdrawals or sickness or death related to medicinal plants?

Side question: Was there ever a time in pre-modern history where medicinal plants were highly sought-after and used as a currency? For example, I would think that the discovery of man's most effective painkiller (opium) would be quite a massive business long before the Chinese/British opium conflicts.

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edit: added coca plant because I forgot about that one :)