Doctors ordered those with heart disease or high blood pressure to avoid them completely.
Just two cans a day of drinks with caffeine and taurine were shown to have an impact.
They caused blood pressure to rise significantly, even in healthy people.
Most energy drinks contain caffeine and taurine – an amino acid found in protein-rich foods like meat and fish thought to make people alert.
Both affect heart rate but little is known about their impact on blood pressure.
Researchers studied 15 men and women who didn’t drink any other caffeine beverage for one week.
They measured blood pressure and heart rate before and after drinking two cans of an energy drink.
Within four hours, their blood pressure and heart rate rose by between five and seven per cent.
This increased by almost ten per cent after seven days.
The study was unveiled at the US Heart Association conference in Orlando, Florida.