You’ve seen them in grocery stores and gas stations, energy drinks proposing a timeline of effectiveness with just their name. But what’s the difference between 5 and 7 Hour Energy? 
Answer: The number in the name – that’s it! If it says 7 hour energy, a tiny part of your subconscious will be on board, thinking OK, I am totally alert now. Alas my friends, this is the Placebo Effect. The truth is caffeine has a half-life of three to six hours (different metabolisms mean different rates of caffeine break-down), so regardless of what it says on the label, 3-6 hours later, only half the original dose of caffeine is still active and effective in your system. This is why it pays to enjoy the energy drink over several hours – NEVER, EVER, EVER CHUG AN ENERGY DRINK!!! It is SO not good for your heart or brain – it’s like an ambush, or like setting the treadmill to 8mph before you even step onto it.
Allow me to explain: Caffeine metabolism 101:

Caffeine absorption occurs minimally through stomach and mostly occurs through the small intestine. Virtually all caffeine is completely absorbed and is evenly distributed throughout the body. Caffeine is one of the few substances that can actually permeate the blood-brain barrier. Caffeine starts affecting the body as soon as 20 minutes. Maximum blood concentration occurs around 30 minutes.   
 ***Tip: Challenge yourself to drink only half a serving (you’ll be pleasantly surprised when you become awake and alert and still have half a can for later! If you are still tired after 30 minutes, THAT’S when you know for sure you need another sip or two.)

Understanding this timing is key to understanding why drinking a whole can of energy drink in less than 20 minutes is a bad idea. If you enjoy the energy drink over several hours, you can prolong the window of time that caffeine is at its peak concentration in the blood. If you chug the whole can, the concentration of caffeine molecules in your blood will surge, then disperse and decrease, like an ocean wave. Crack open the can – here comes the wave and there it goes…Tired again. 
Ever wonder why 5-hr Energy makes a big deal about avoiding the energy crash? Part of it is portion control. It is more concentrated than a full can of Rockstar or Monster, but you’re also less likely to overdo it. If you drink the whole 16 oz can of Monster, you will absorb the caffeine and start the clock on its degradation. On the contrary, if you slowly sip the energy drink, the continuous dose is like slowly turning up the volume on a car radio. The level of caffeine in the blood, like the volume, will stay elevated. Also like in a car, know your own limits and you’ll avoid the crash.