The psychoactive effects of caffeine are massive after you detox for a few weeks. I had a full cup after not having caffeine for a month and the effect was massive. Near euphoria, constant task switching, some anxiety, etc. I personally felt the effect was much stronger than weed has ever felt for me and comparable to having 5+ drinks of alcohol.

But the effect quickly drops to almost nothing very rapidly. I started having caffeine 3 out of 7 days because having a low caffeine tolerance was too annoying. One coke, tea, chocolate would completely destroy my sleep.