Alert brain: The stimulating effects of caffeine cause alertness right away. It can also temporarily relieve drowsiness and fatigue.
Confusion: Too much caffeine can overstimulate the brain, leading to confusion.
Headaches: A headache can occur from either too much caffeine or as a symptom of caffeine withdrawal. But in small amounts, it may relieve symptoms of a hangover.
Decreased suicide risk: One study found that the mood-enhancing effect of caffeine was linked to a 45 percent lower risk of suicide in participants.
