By Catherine Burns
Newsbeat Health Reporter
The drink is supposed to help you concentrate
The adverts claim it "gives you wings" but experts say the energy drink could have some more serious side-effects.
A medical team in Australia tested how it affected 30 young adults.
They checked their blood systems, and then gave them a can of sugar-free Red Bull. An hour later, they looked at the blood again, and said it was sticky.
That's what normally happens before you have a stroke.
Scott Willoughby did this research. He said: "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."
He thinks if you're stressed or have high blood pressure, it could be deadly.
The drink is supposed to help you concentrate, and react more quickly. Its makers say you should have a can before doing a race, or when you are about to do a long motorway drive.
But this isn't the first time it's been linked to health problems. It's banned in countries like Norway, Uruguay and Denmark.
Other studies have talked about it increasing your heart rate and blood pressure.
Not surprisingly, Red Bull bosses aren't happy with this.
They point out that a can only has the same amount of caffeine as a normal cup of coffee.
Even so, they say it's best to not have more than a couple a day.
Last year, they sold 3.5 billion cans in 143 countries around the world. They say that is only possible because so many health authorities have decided it is safe.
Nick Mexhaj is a builder, and he gets through 4 cans a day. He's not worried though.
Samantha Kozolowski likes mixing Red Bull with vodka on nights out.
He said: "I can drink loads and I still feel the same. "
Samantha Kozolowski likes mixing it with vodka on nights out. She thinks there are too many scare stories about health.
Samatha said: "It might make me a bit more aware not to go drinking 4 or 5 cans a night, but if I like it, I like it."