Coffee has an acid-based oil that is an irritant to gastric mucosa. It stimulates the secretion of gastric acidity. Secondarily, the high gastric acidity results in secretion of adrenalin. The secretion of adrenalin stimulates insulin secretion with resultant secondary relative hypoglycemia. The end result is tension, a mild rise in blood pressure, and 2-3 hours later craving sweets because of the relative hypoglycemia.
Coffee is more harmful than caffeinated soft drinks or tea.
Mild tea does not cause reactive hypoglycemia and a rise in blood pressure. It has no acid-based oil as does coffee. It contains tannin. Tannin or tannic acid curbs thirst and results in less demand for further consumption of tea or coffee. Coffee and tea both temporarily raise the body temperature.