Anna Svatikova, M.D., Ph.D., of the Mayo Clinic, Rochester, Minn., and colleagues randomly assigned 25 healthy volunteers (age 18 years or older) to consume a can (480 mL; 16 fl. oz.) of a commercially available energy drink (Rockstar; Rockstar Inc) and placebo drink within 5 minutes, in random order on 2 separate days, maximum 2 weeks apart. The placebo drink, selected to match the nutritional constituents of the energy drink, was similar in taste, texture, and color but lacked caffeine and other stimulants of the energy drink (240 mg of caffeine, 2,000 mg of taurine, and extracts of guarana seed, ginseng root, and milk thistle). This JAMA study is being released to coincide with its presentation at the American Heart Association's Scientific Sessions 2015. 
 
 Energy drink consumption has been associated with serious cardiovascular events, possibly related to caffeine and other stimulants. The researchers examined the effect of energy drink consumption on hemodynamic changes, such as blood pressure and heart rate. Participants were fasting and abstained from caffeine and alcohol 24 hours prior to each study day. Serum levels of caffeine, plasma glucose, and norepinephrine (noradrenaline) were measured and blood pressure and heart rate were obtained at baseline and 30 minutes after drink ingestion. 
 
 Caffeine levels remained unchanged after the placebo drink, but increased significantly after energy drink consumption. Consumption of the energy drink elicited a 6.2 percent increase in systolic blood pressure; diastolic blood pressure increased by 6.8 percent; average blood pressure increased after consumption of the energy drink by 6.4 percent. There was no significant difference in heart rate increase between the 2 groups. The average norepinephrine level increased from 150 pg/mL to 250 pg/mL after consumption of the energy drink and from 140 pg/mL to 179 pg/mL after placebo (change rate: 74 percent vs 31 percent, respectively). 
 
 "These acute hemodynamic and adrenergic changes may predispose to increased cardiovascular risk," the authors write. "Further research in larger studies is needed to assess whether the observed acute changes are likely to increase cardiovascular risk." 
 
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 (doi:10.1001/jama.2015.13744; Available pre-embargo to the media at http:/media.jamanetwork.com 
 
 Editor's Note: This research was supported by a grant from the Mayo Foundation and the National Center for Advancing Translational Sciences, National Institutes of Health. The authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest and none were reported. 

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 Having just one energy drink can cause short-term changes in healthy adults that, over time, could increase their risk of heart disease, a new study finds. 
 
 In the study, participants who drank one 16-ounce (480 milliliters) can of Rockstar energy drink had higher blood pressure and higher levels of the hormone norepinephrine, after they drank the energy drink than before they consumed it. Norepinephrine is released by the adrenal glands and raises blood pressure; it is a cousin of the hormone adrenaline. 
 
 One Rockstar energy drink contains 240 milligrams (0.008 ounces) of caffeine, along with other stimulants, including 2,000 mg (0.8 ounces) of taurine and extracts of guarana seed, ginseng root and milk thistle, according to the study. [5 Health Problems Linked to Energy Drinks] 
 
 To test the effects of the drink, the researchers recruited 25 healthy adults to participate in the study. On two separate days, the researchers measured the volunteers' blood pressure, heart rate and blood levels of caffeine, glucose and norepinephrine. The researchers then asked the participants to consume either the energy drink or a placebo. The placebo was similar in taste, texture and color to the energy drink, but did not contain caffeine or other stimulants. 
 
 Thirty minutes after the participants finished each drink, the researchers repeated their measurements. The volunteers also underwent several tests that increased their physical and mental stress. During these stress tests, the researchers once again measured blood pressure and heart rate. 
 
 After consuming the energy drink, the participants' systolic blood pressure increased, on average, by 6.6 points (from 108.4 mm Hg to 115.0 mm Hg), compared with an average increase of 3.3 points (from 108.3 mm Hg to 111.6 mm Hg) after drinking the placebo. 
 
 Norepinephrine levels also increased following the consumption of the energy drink. They rose, on average, 100 picograms per milliliter (from 150 pg/mL to 250 pg/mL), compared with an average increase of 39 pg/mL (from 140 pg/mL to 179 pg/mL) after drinking the placebo. 
 
 The changes seen in the study "may predispose [people] to increased cardiovascular risk," the researchers wrote in their study. 
 
 This is not the first study to suggest energy drinks may have a negative effect on heart health. In a study from earlier this year, the same research group found that energy drinks can raise people's blood pressure to potentially unhealthy levels. 
 
 However, the researchers noted that additional, larger studies are needed to confirm the results of the new research. The current study's limitations include the small sample size of adults and the use of only one type of energy drink, the researchers wrote. 
 
 Live Science reached out to Rockstar Inc. for comment, but did not hear back by press time. 
 
 The study was published in the journal JAMA today (Nov. 8) and was also presented at the American Heart Association's Scientific Sessions meeting, held in Orlando, Florida. 
 
 Follow Sara G. Miller on Twitter @SaraGMiller. Follow Live Science @livescience, Facebook & Google+. Originally published on Live Science.
– A single can of an energy drink packs quite a wallop, causing potentially worrisome spikes in blood pressure and in a stress hormone that's a cousin to adrenaline, say researchers at the Mayo Clinic. Reporting in the journal JAMA, the Mayo team recruited 25 healthy adults for the study and measured the volunteers' blood pressure, heart rate, and levels of caffeine, glucose, and the hormone norepinephrine in their bloodstream before and after ingesting the energy drink Rockstar. They simultaneously tested a placebo that looked and tasted similar but lacked the caffeine and stimulants such as taurine and milk thistle extract found in the energy drink, the researchers report in a press release. While heart rate didn't change significantly after a person drank one serving of Rockstar, average blood pressure increased by 6.4%, while average norepinephrine levels went up 31% after taking the placebo versus 74% after downing the energy drink. "These acute hemodynamic and adrenergic changes may predispose to increased cardiovascular risk," they write. The same group had earlier this year found that energy drinks can raise blood pressure to potentially unhealthy levels, reports Live Science, though they warn that larger studies will be required to confirm this study's results because the sample size is so small and involved just one type of energy drink. (Little evidence backs up the claim by energy drink makers that ingredients other than caffeine increase energy levels.)