A teenage boy who died after drinking three caffeinated drinks in less than two hours had no pre-existing heart problems, a coroner has said.

South Carolina student Davis Cripe had drunk a large fizzy drink, a latte and an energy drink in the two hours before he collapsed.

It was ruled that the student died after his heart fell out of rhythm due to the amount of caffeine - estimated to have been around 500 milligrams - ingested into his system over such a short period of time.

Schoolmates at Spring Hill High had said the 16-year-old had "chugged" the large bottle of energy drink before becoming ill during a lesson.

The final drink is believed to have caused the cardiac arrhythmia (irregular heartbeat) which led to his death an hour later.

Stressing that it was the speed at which the caffeine was drunk rather than the actual amount, the coroner said "the same amount of caffeine on another day may have been right".

The coroner went on to compare caffeine to other stimulants, saying: "We believe people need to pay attention to their caffeine intake and how they do it, just as they do with alcohol or cigarettes."

Davis' father, Sean, who said he was "brokenhearted" by his son's death, appealed to parents to "talk to your kids about the dangers of energy drinks", and pleaded with young people to "stop buying them".

American medical research group the Mayo Clinic say on its website that "up to 400 milligrams of caffeine a day appears to be safe for most healthy adults". That is the equivalent of around four cups of coffee.