A study of university students found drinking one 250ml can of the sugar-free version of the energy drink that 'gives you wings' increased the 'stickiness' of the blood and raised the risk of life-threatening clots.
Dr Willoughby, of the Cardiovascular Research Centre at the Royal Adelaide Hospital, said he was 'alarmed' at the results and would not drink Red Bull himself.
Those with underlying heart or circulatory problems should think twice before buying the caffeine-loaded drink, he said.
Red Bull is banned in Norway, Uruguay and Denmark because of health fears, but the company last year sold 3.5 billion cans and bottles in 143 countries.
In Britain alone, it has sales of £271 million a year, with much of the cash spent in bars and clubs were it is a popular mixer with vodka and other spirits.
More: Daily Mail