Caffeine has a half-life of about 5 hours. That means that if you consume 200 mg of caffeine, after 5 hours, you'll still have 100 mg in your system. And after 10 hours, you'll still have 50 mg in your system. So it takes a while for caffeine to completely clear out of your system. If you're someone who is sensitive to caffeine, you might feel the effects for even longer. Caffeine can stay in your system for up to 14 hours, so it's best to limit your intake if you're trying to avoid its effects.