Caffeine is a psychoactive stimulant that the FDA classifies as GRAS: “Generally Recognized as Safe.” Harmless and potentially helpful in small doses, excessive caffeine intake can raise blood pressure and cause dehydration, headaches, anxiety, insomnia, nausea, and rapid or irregular heartbeat. A massive overdose of the type experienced by Anais Fournier can be lethal.
As with most substances, moderation is key. FDA research indicates that a moderate amount of caffeine generally equates to 100-200 mg per day; anything above this amount can cause adverse symptoms such as arrhythmia (irregular heartbeat), insomnia, and anxiety. To put this into perspective, two cans of Monster puts you over this threshold, at 240-480 mg of caffeine (depending on the size of the cans).
In energy drinks, the effects of caffeine peak within the first hour of consumption, at which point a sugar crash occurs. Despite the effects waning very early on, caffeine usually stays in the bloodstream for a full 12 hours. After the 12-hour period, withdrawal can occur; symptoms include headaches and irritability.
This timeline may account for many consumers’ tendency to drink additional caffeinated beverages once that sugar crash occurs, rather than waiting for the full 12-hour cycle to conclude. Unfortunately, consuming more and more caffeine only builds your tolerance to it. When you consistently drink a lot of energy drinks, you have to consume increasing quantities over time in order to achieve the same jolt of “energy.”