How often can one drink an energy drink?

Avoid it. It is not healthy. It has very high sugar and Caffine content. 5 times more than a cup of coffee. It makes you more alert for a short time, but it can cause Arrythmia. You should develop better time management skill and not dependent on energy drink for "energy". It gives false sense of control. You also will get addicted to it. And if mixed with alcohol, can be fatal.