I have to confess that I am an occasional consumer of 5-Hour Energy. I started trying it out after a friend at work reported "benefits". I consume it quite rarely, maybe once a month or so, usually if I have had a heavy lunch and am trying to stay alert or if I am planning to go to the gym and am not quite feeling up to it.
As far as the actual effect is concerned, I would describe it as mild but noticeable, a level of alertness that while not significant, stands out from the noise. In fact it's as noticeable...as a cup of coffee. And that seems to be the conclusion many sources, including the New York Times, are drawing about a variety of energy drinks including 5-Hour Energy, Monster and Red Bull. Energy drinks have been in the news recently, especially in connection with about 20 or so fatalities connected to the whole spectrum of the various brands. The verdict on these fatalities is still out there since it's very difficult to establish a causal connection in such cases, but what's an unquestionable fact is that these drinks are now available in every convenience store in the country and countless bottles are consumed every year. They are the new Gatorade. Anything of that magnitude needs to be rigorously probed and scrutinized since it has the potential to affect the well-being of millions.
An article in the New York Times today investigates whether there are any more benefits to energy drinks than those provided by a regular cup of coffee. It cites the opinion of various experts who seem to agree that the principal - and in their opinion the only important - ingredient in these concoctions is caffeine. According to these experts, basically what you are paying for is an overpriced bottle of caffeine, more expensive than a NoDoz pill and even a Starbucks coffee.
The other ingredients mainly seem to serve the purpose of window dressing and advertising. For instance there's taurine, an amino acid with an unusual structure sporting a sulfonic acid group. Taurine is generally not regarded as an essential amino acid, although studies have implicated it in a variety of physiological functions. Taurine can be synthesized in the body from the amino acids cysteine and methionine. More importantly, it is present in copious amounts in meat which means that most meat-eaters will get enough of it from their diet. The taurine in energy drinks thus seems to be superfluous.
Another common ingredient in the drinks is good old vitamin B12. Vitamin B12 is also a major staple of animal derived foods and is also part of certain man-made foods like fortified breakfast cereal. The recommended dietary allowance (RDA) for B12 is about 2.4 micrograms for an adult male or female. As a comparison, you can get 6 micrograms from a serving of breakfast cereal specially fortified with B12 or 1.2 micrograms from a cup of low-fat milk. Thus, two cups of milk should ideally provide you with your B12 RDA. Energy drinks contain upto 200 micrograms of the vitamin, or more than 8000% the RDA. It's worth noting that B12 is a water-soluble vitamin, so most excess amounts are simply going to be excreted; even the spokesperson for 5-Hour Energy acknowledges this. The same goes for the other vitamin B in the brands, B6.
Other ingredients are of a similar type; common dietary substances whose amounts vastly exceed their RDAs. For instance there's glucuronolactone which is a precursor for vitamin C synthesis. Vitamin C itself is of course another substance whose excesses have been famously questioned for more than half a decade, most notably after Linus Pauling prescribed it as a panacea. The same goes for the other additives in energy drinks. At best their functions in the body are under investigation, and the benefits of excesses are definitely up in the air. The studies done on the value of large quantities of these substances suffer from a variety of limitations; many of them are done on rats for instance, and anyone who is involved in drug development knows how different rats and humans can be as test subjects. Thus it is completely fair to question if these drinks provide anything other than a concentrated dose of caffeine.
However there is one possible mechanism that I can think of which could possibly make the caffeine in these drinks somewhat different from that in other formulations. The reason the Times report made me ponder is because it led me back to the original reason why, after trying out 5-Hour Energy once, I started occasionally sampling it. The reason was that black coffee and NoDoz both gave me headaches; for some reason 5-Hour Energy did not. Now doctors have known for centuries that the presence of certain foods in the stomach can affect the way drugs and other organic molecules are absorbed and metabolized. Recent studies lead credence to this observation; for instance drinking grapefruit juice can significantly enhance the blood levels of certain widely prescribed drugs like statins. What basically happens is that the other ingredients block key proteins in your digestive system that would usually metabolize the drug of interest; this leads to less of the drug being broken down and more of it being absorbed intact. In case of 5-Hour Energy, I wonder if the other ingredients, even while providing no benefits of their own, somehow enhance the absorption and effects of the caffeine.
This is just a wild hypothesis. My experience of 5-Hour Energy giving me a caffeine buzz without a headache is as anecdotal as the hundreds of anecdotal comments that usually erupt when articles on energy drinks are published. In fact I would be the first to admit that even the slight enhancement I feel from 5-Hour Energy is entirely a placebo effect. However my hypothesis is a testable hypothesis, the testing of which might illuminate other properties of energy drinks. The truth is that without controlled experiments which test the effects of the ingredients individually and then in combination using the exact same formulation (which unfortunately is proprietary) it will be hard to tease out any potential effects of these extra ingredients. They could possibly have the kind of caffeine-enhancing property that I mentioned, although this is only a conjecture. But based on what we know about human physiology and dietary allowances, it seems much more likely for now that these drinks are little more than caffeine shots packaged in a fancy wrapper. The burden of proof still lies with the manufacturers.