'Everything will be fine once caffeine kicks in', is a common belief among tea coffee lovers. But do you know exactly what is caffeine? Caffeine mostly found in tea, coffee, cola and some chocolates is a type of drug that stimulates the nervous system of our body. Caffeine in Irish Breakfast Tea has certain benefits and side effects. The content of caffeine in Irish Breakfast Tea is 40.00 mg. Caffeine can be effective on headaches and can increase alertness but, very high doses of Irish Breakfast Tea caffeine can have adverse effects on our body. So, Irish Breakfast Tea caffeine content should be as low as possible. Also, get to know caffeine content of other products like Irish Breakfast Tea vs Affogato, Coffee vs Affogato.