 It's important to understand your threshold, how you react to caffeine, how much you're having, how you're dosing it throughout the day. For most people, the US Food and Drug Administration says moderate caffeine consumption can be part of a healthy diet, but overuse can lead to side effects like insomnia, anxiety and nausea. Since caffeine affects everyone differently, Zupano says to measure how much you can handle without having any of those negative side effects.