However I paid for it later. As soon as I left the library I noticed I was dizzy, queasy, off-balance, and nauseous. I was still a little jittery, and literally my fingers had been twitching since I took the five hour energy shot. I felt like I was a psychotic robot. My joints weren't working properly and I was using any stable object to help me walk to my car. Somehow I drove the hour ride home without any incident, but I remained nauseous until the following evening about 30 hours later. And I hate being nauseous. For that reason I will never take one of these again, but I wanted to do some research on it.
According to the Mayo Clinic, other, more serious side effects include “liver toxicity, worsening of stomach ulcers, and altered blood sugar or insulin levels or uric acid concentrations” (source)
Since 5-hour energy falls under Dietary Supplement Health and Education Act that stipulates drinks made from healthy substances, vitamins, and herbs; it does not have to be regulated by the government and that it falls to the company to ensure that its products don't have a negative effect. Amongst the negative effects that are quoted above, is a "Niacin Flush" that elevates blood pressure, blood circulation causing body temperature increase, because of the high levels of Niacin present.(source) This is probably partially what I experienced and my system just couldn't handle it.
One specific tactic 5-hour energy uses to market is that their product is healthy because it contains good vitamins in addition to the caffeine that ensures increased mental capacity and energy. However, consuming 8000% B12 and 2000% B6 isn't going increase your mental capacity right away. The majority of that will just be flushed through your system without any benefit, and will actually overwork your system with the excess it doesn't need. And that isn't even including what the caffeine is doing to your system.
Overall, 5-hr energy shots are not FDA regulated or approved and their dangers have not been fully uncovered. If you are going to use 5-hour energy shots do it sparingly, and since regular contains as much as a cup of coffee, and the extra strength contain as much caffeine as from 12 oz. worth of coffee you need to be careful about how much you take at a time (source). If you can continue on without any that would be best.
"These energy shots have over a dozen ingredients all together, and consumers are ingesting them at very high doses but there is no research of how the ingredients react all together," Bauer said. (source)