The caffeine-loaded beverage, popular with university students and adrenaline sport fans to give them "wings," caused the blood to become sticky, a pre-cursor to cardiovascular problems such as stroke.
"One hour after they drank Red Bull, (their blood systems) were no longer normal. They were abnormal like we would expect in a patient with cardiovascular disease," Scott Willoughby, lead researcher from the Cardiovascular Research Centre at the Royal Adelaide Hospital, told the Australian newspaper.
Red Bull is banned in Norway, Uruguay and Denmark because of health risks listed on its cans, but the company last year sold 3.5 billion cans in 143 countries. One can contains 80 mg of caffeine, around the same as a normal cup of brewed coffee.
The Austria-based company, whose marketing says "Red Bull gives you wings," sponsors Formula 1 race cars and extreme sport events around the world, but warns consumers not to drink more than two cans a day.
