Although the caffeine that occurs in tea is the same as the molecule in coffee, it has remarkably different effects. When you drink a cup of coffee, caffeine diffuses into the bloodstream very quickly, reaching the brain in less than 5 minutes. This generates the well-known coffee “rush,” whose effects dissipate in 2 to 3 hours.
The caffeine contained in tea is coated with polyphenols, and these molecules are released gradually over a period of up to 10 hours. Tea provides long-term stimulation. This is why caffeine in tea is classified as a mild stimulant, while that in coffee is considered to be more powerful.
Besides that, the same cup of tea contains less caffeine than coffee, and it's easier to control the level of caffeine in tea by varying the brewing techniques. Decreasing the water temperature and brewing time will reduce the amount of caffeine in a tea cup.