1 OPINION. 2  The screening process for Syrian refugees is much more rigorous than for other visitors coming to the U.S. (AP Photo/Hassan Ammar)
About 250 milligrams of caffeine â or the equivalent of 2 to 2 1/2 cups (473 to 591 milliliters) of plain, brewed coffee â a day may cause this effect. If you have type 2 diabetes and you're struggling to control your blood sugar levels, limiting the amount of caffeine in your diet may provide a benefit.
Ingesting 95 mg of caffeine can spike your blood pressure three to 14 points. Based on that assessment, drinking two or more cups of black tea would provide more than enough caffeine to affect your blood pressure.