A news article making the rounds describes a study in which subjects drank two energy drinks a day for a week. Their blood pressure rose by about eight percent on the first day, and stayed high for the week. The subjects had an average age of 26, and were otherwise healthy. They did not engage in strenuous exercise during the study.
The message is clear: energy drinks can raise your blood pressure, which may be ok for healthy people, but an eight percent increase in people with pre-existing hypertension may be more than they can stand.
But the significance of this finding is not easy to parse.
First, energy drinks have three important ingredients that could impact blood pressure: caffeine, taurine, and glucoronolactone. In the study, and in most energy drinks, the caffeine content was 80mg. An eight oz cup of coffee is about 110mg, and a 12 oz Pepsi is about 50 mg. In this study, they were drinking two drinks a day. Does caffeine increase your blood pressure? It does acutely, but habitual caffeine drinkers eventually become tolerant to the blood pressure effects, and, for example, chronic coffee drinkers (e.g. > 1 per month) do not have higher blood pressures than before they ever drank coffee. This study ran one week, so it is conceivable that if these subjects were not ordinarily used to drinking caffeine, the 160mg/d could have been at least partly responsible. However, and this is the point, if they were regular coffee drinkers, the 160mg would not have been likely to have caused it.
This brings us to taurine and glucoronolactone - which is actually a metabolite of glucose, but also a precursor to taurine. The study used a drink that contained 1000mg of taurine and (probably) 600mg of glucoronolactone. Strangely, taurine has been found to decrease blood pressure in mice and men, and possibly prevent weight gain (which is different from causing weight loss), and decrease blood sugar. And it is found in meats at about 200mg/kg.
So it isn't evident why these subjects had an eight percent increases in their blood pressure, unless they were all rare caffeine users in the past.
Interestingly, serum taurine is known to be elevated in depression. This shouldn't be taken to mean that taurine causes depression; rather it is more likely that depression is associated with impairment in taurine transport from the blood to the brain, and so it accumulates in the blood. Antidepressant treatment reduces the serum taurine levels, thus likely increasing the transport to the brain. Taurine in high doses is actually a mild sedative, as it binds to GABA-A receptors (similar to alcohol.)
So it isn't clear what effects energy drinks have on the body, beyond the obvious stimulation. It would be prudent to avoid them if you are sensitive to caffeine or blood pressure changes.