That is very dependent on the consumed quantity, and the time of consumption.
And is nothing compared to the next most frequently used drugs, alcohol and nicotine, hell it has plenty of positive effects.
So my initial statement I believe still stands that humanity could hardly happen upon another substance that they could use in such a huge amounts with minimal negatives.
You could say the same thing for most amphetamines.
I don't think caffeine is particularly harmful, but it is a huge stretch to paint it as purely beneficial and without side effects. As a point of fact most people getting their "morning jolt" are just treating the side effects of extended caffeine usage - they are physically addicted.
About once a year I spend a month doing no caffeine. Every single year it is quite illuminating to do through first withdrawal and then to experience the first cup of coffee. I recommend it, and you might change some of your thoughts on caffeine if you do this.
And is nothing compared to the next most frequently used drugs, alcohol and nicotine, hell it has plenty of positive effects.
So my initial statement I believe still stands that humanity could hardly happen upon another substance that they could use in such a huge amounts with minimal negatives.