"Because of the previously mentioned health concerns arising from the consumption of caffeine, it seems appropriate that warning labels should accompany all caffeinated beverages," says the study, published in this month's Journal of Analytical Toxicology.
The research team analysed the caffeine content of 10 energy drinks and 19 fizzy sodas, all widely available.
They found all the fizzy drinks had caffeine levels well inside the 65mg per 12oz serving recommended limit for cola drinks in the US. Most energy drinks had levels in the high 60s and 70s for an 8oz serving.
Dr Bruce Goldberger, one of the researchers, said he was surprised by the high caffeine content of some of the energy drinks. He pointed out that only four of the 10 were labelled with some sort of warning to consumers.
Goldberger, nevertheless, said all drinks containing caffeine should display the caffeine content on their labels, to prevent those at risk from consuming too much caffeine.
"In certain people, consumption of caffeine causes serious health effects, such as anxiety, palpitations, irritability, difficulty sleeping and stomach complaints," he said.
Other studies have indicated moderate caffeine intake could lower consumers' risk of liver disease.
Both the American Dietetic Association and the UK Food Standards Agency advise people not to consume more than 300mg of caffeine per day. Their advice is particularly aimed at pregnant women, who, studies indicate, have greater risk of miscarriage or babies with low birth weight if they exceed the 300mg barrier.
Roland Griffiths, professor of behavioural biology at John Hopkins University, said people could become addicted to caffeine on just 100mg per day.
"People should make informed decisions about their caffeine use. Obviously, knowing how much caffeine a given product contains is critical to making an informed decision about use."
Calls for mandatory caffeine labelling on ordinary fizzy drinks expands a debate that has been hanging over the energy drinks sector for a number of years.
The flagship of the energy drinks sector, Red Bull, is still banned in France on the advice of the country's health and food safety authorities, partly because of concerns at the drink's high caffeine levels.
A 2002 European Union directive states that all drinks containing caffeine, except tea and coffee, above 150mg per litre must state 'high caffeine content' on their labels. Accordingly, Red Bull cans in the UK now carry this label.
Red Bull and other energy drinks' makers have repeatedly stated that their products are safe.