You may be surprised at how much you know.
Caffeine is a stimulant.
As a stimulant, too much caffeine can have many side effects. Excessive intake can cause restlessness, insomnia, heart irregularities, and delirium. In moderation, caffeine is a mild stimulant that increases urination and the heart's rate. Decaffeinated coffee and teas have no caffeine whatsoever. Even though these drinks should have no caffeine, most contain at least a small amount.