Performance-enhancing energy drinks should carry prominent health warnings to protect young people from overdosing on caffeine, doctors said yesterday.

The warning follows research in the US into 28 energy drinks that found some contained up to 14 times as much caffeine as a can of cola, or the equivalent of seven cups of strong coffee.

The market for caffeine-rich energy drinks has exploded in recent years, causing some doctors concern at the lack of regulations to ensure they are consumed safely.

In the UK, drinks containing more than 150mg caffeine per litre must be labelled as "high caffeine content", but there is no upper limit on the amount of caffeine, nor do drinks need to carry warnings about the potential risks of caffeine overdose.

The Food Standards Agency advises pregnant women not to exceed 300mg of caffeine a day.

Roland Griffiths at Johns Hopkins University in Maryland surveyed caffeine levels in energy drinks widely available in the US and found they varied from 50mg for a drink called "Whoop Ass" to 505mg in a drink called "Wired X505". A can of cola contains around 35mg and a cup of coffee around 75mg.

Photograph: Austin Hargrave

Some of the drinks are not available in the UK, but one brand, called Cocaine Energy Drink, was launched in Britain last month. It contains 280mg caffeine, or eight times as much caffeine as a can of cola. One of the best-selling energy drinks in the UK, Red Bull, contains 80mg caffeine.

"What we've seen since the first energy drinks arrived on the shelves is a sea change in how caffeine is being marketed," said Prof Griffiths. "These drinks are being very aggressively marketed, often to kids interested in extreme sports, and some of them are making overt appeals to the illicit drug culture. You can easily imagine people consuming a couple of these drinks and running smack into caffeine intoxication. People can end up not only feeling lousy, but in ER thinking they're having a heart attack."

People who drink tea and coffee regularly build up a tolerance to caffeine, but Griffiths says younger people are at risk of overdosing if they consume highly caffeinated energy drinks at an early age.

Writing in the journal Drug and Alcohol Dependence, Griffiths calls for energy drinks to carry the same kinds of warnings as caffeine pills, which can be bought over the counter at chemists to alleviate drowsiness. Those labels highlight the risks of having too much caffeine, including anxiety attacks, nervousness, rapid heart beat and nausea.

"There's no reason to have a drink on the market that is so caffeinated that if you consume it, the majority of the population is going to experience caffeine toxicity," he said. "For someone who's sensitive to caffeine, 200mg is enough for them to have many of the symptoms of caffeine intoxication."

In the study, Griffiths highlights the cases of nine patients treated by a US poisons unit after having an energy drink called Redline, which contains 250mg caffeine. Eight of the nine were boys, with the youngest aged 13. Their symptoms ranged from nausea and vomiting to tremors, chest pain and a racing pulse.

Earlier this month, the anti-drugs advisory group Drug Education UK warned that schoolchildren are becoming dependent on energy drinks to boost their performance.

Jamey Kirby of Redux Beverages in Las Vegas, which makes Cocaine Energy Drink, said the drinks are labelled with their caffeine content to help children and adults consume them safely.

"Energy drinks are coming under attack because of the branding and marketing strategies. If we were hurting people, we'd be having our ass sued off by now. If you look at the demographic we are going for, it's great news to have these people coming out and saying ban them."