Your genetics actually impact the effect that caffeine has on you. If you are a fast caffeine metabolizer, your body processes caffeine faster and you are at a lower risk of having negative side effects after consuming caffeine. If you are a slow metabolizer, your body takes a longer time to process caffeine and you may need to limit your intake to avoid negative effects.
Whether you are a fast or a slow caffeine metabolizer, it is important to follow the recommendations to consume no more than 400mg of caffeine (about 4 cups of coffee) per day.