When I came to devotees' association, I was again and again asked to quit coffee and tea. I tried to drink other possible drinks, but i was forcefully attracted towards these two drinks. Then I started to pray Krishna and Prabhupad to show some or the other way.
One fine day, I received a video through watsapp, in which a good doctor was explaining how they act upon us.
The very first thing they do is, boosting our nervous system very speedly . And only in twenty minutes, whole nervous system suddenly get down. So the person feel very much fatigue. He/she thinks if I get another cup, I will feel energetic. But actual result is, our nervous system will loose natural control on boosting itself.
Second and another dangerous result is these drinks make people always feel sad, guilty, unwantedly thinking about past and overthinking about very small issues .
So many fights starts by this in their relationships.
That's why if we want not to be sad( depressed) always, and to avoid gastric, indigestion, bp , we should completely avoid t these two drinks.
Hope my experience help atleast few people