Caffeine is harmful in that it is highly addictive.
That's a matter of opinion. I consume it but am not addicted. This is the same as claiming drinking milk or eating candy is a dangerous addiction. As I said, too much of anything is bad but these things in moderation are not.
Caffeine: How much is too much? - Mayo Clinic
"Up to 400 milligrams (mg) of caffeine a day appears to be safe for most healthy adults. That's roughly the amount of caffeine in four cups of brewed coffee, 10 cans of cola or two "energy shot" drinks."
Caffeine: how does it affect our health?
"The US Food and Drug Administration (FDA) state that the average amount of
caffeine consumed in the US is approximately
300 mg per person per day - the equivalent to between two and four cups of
coffee. This is considered to be a moderate caffeine intake, which according to many studies,
can promote a variety of health benefits."
"Caffeine acts as a stimulant by activating the
central nervous system. It can combat
tiredness and improve concentration and focus."
"
Caffeine's potential health benefits
As well as its stimulating effects, caffeine has been heralded for providing
an array of health benefits.
Some studies have suggested that drinking three or four cups of coffee a day may reduce the risk of liver, mouth and throat cancer.
Last year,
Medical News Today reported on a study suggesting that consuming three cups of coffee a day may
reduce the risk of liver cancer by 50%, while another study suggests that drinking four cups a day could
halve the risk of mouth and throat cancer.
Caffeine consumption has also been associated with positive effects on the brain.
Last year, a study from the Harvard School of Public Health suggested that drinking between
two and four cups of coffee a day may reduce suicide risk in adults, while more recent research found that ingesting 200 mg of caffeine each day may boost long-term memory.
Other studies have also suggested that caffeine intake may protect against type 2 diabetes, Parkinson's disease, cardiovascular disease and stroke."