You may be caffeine sensitive if you experience physical or mental side effects like shakiness, anxiety symptoms, jitteriness, trembling, nausea, or insomnia even when consuming less than 400 milligrams of caffeine per day, the amount in about three 8-ounce cups of coffee. (7)Doctors don’t have set criteria to diagnose caffeine sensitivity, so your best bet is to limit how much caffeine you drink if you find yourself experiencing negative side effects.