Normal caffeine intake for a healthy adult is generally considered to be up to 400 milligrams per day, which is roughly the amount found in about four cups of brewed coffee. At this level, caffeine can improve alertness and concentration without causing significant side effects for most people. Sensitivity varies, though—some individuals may feel jittery or experience sleep disruption at lower amounts, so moderation and timing, especially avoiding caffeine late in the day, are important.
