Sure some of it is a natural part of our physiology. Do a little more digging and you will see how many "drugs" are naturally occurring in larger or smaller amounts in plants, barks, roots, leaves, etc. How plants and their components affect our neurotransmitters, etc.

Where's the limit? Or what's the limit?

Do you eat chocolate? Chocolate has caffeine and theobromine.

Do you like to eat chocolate? Or sugar? Why do you like to do that?

The list is almost endless. We can continue all day until we find enough examples from your everyday life.

So let's call it what it is.