For many years I go to the same vacation spot (kayaking in the most beautiful nature place I have seen) and go cold-turkey. I didn't notice any side effects of lack of coffee besides slower muddier thinking. After I go back and start drinking coffee, feel back to normal.

I also had a very big life altering mental health incident very recently, drank A LOT of coffee during and I feel it helped, now I am much more calm, "more correct" despite drinking coffee like before.

Based on this I posit that coffee is used by humans to offset unwanted mentality changes, not a cause of unwanted mentality changes.