Energy drinks give you temporary energy from caffeine and sugar (unless it is a sugar-free energy drink like I prefer). The caffeine increases your metabolism and thus gives you more energy and mental alertness. It may give you energy during certain activities but not always during high intensity exercise, especially if it dehydrates you. The massive amount of sugar content in regular energy drinks can spike your blood sugar and give you an initial rush of energy, but then you will crash around an hour later. The sugar-free energy drinks rely solely on the caffeine and other stimulant content to provide you with extra energy, even though you will also crash after the caffeine high ends. Energy drinks may give you a temporary energy boost but they are not very healthy and no match for a healthy diet (including complex carbs) and workout program. That being said, it is all up to you and your personal choices for caffeinated drinks and supplements.