This is because the drink can cause blood potassium to drop dangerously low, they report in the International Journal of Clinical Practice.
They tell of the curious case of an Australian ostrich farmer who needed emergency care for lung paralysis after drinking 4-10 litres of cola a day.
He made a full recovery and was advised to curtail his cola drinking.
Another example included a pregnant woman who regularly consumed up to three litres a day for the last six years and complained of tiredness, appetite loss and persistent vomiting.
A heart trace revealed she had an irregular heartbeat, most likely caused by her low blood potassium levels.
Once she stopped drinking so much cola, she made a full and uneventful recovery.
The investigators believe these cases are not atypical and that many people risk problems due to their intake.
Manufacturers insist the products are safe when consumed in moderation.
In a commentary, Dr Clifford Packer from the Louis Stokes Cleveland VA Medical Centre in Ohio said: "We have every reason to think that it is not rare.
"With aggressive mass marketing, super-sizing of soft drinks, and the effects of caffeine tolerance and dependence, there is very little doubt that tens of millions of people in industrialised countries drink at least 2-3 l of cola per day.
"It follows that the serum potassium levels of these heavy cola drinkers are dropping, in some cases, to dangerous low levels."
The author of the research paper, Dr Moses Elisaf from the University of Ioannina in Greece, said it appeared that hypokalaemia can be caused by excessive consumption of three of the most common ingredients in cola drinks - glucose, fructose and caffeine.
"The individual role of each of these ingredients in the pathophysiology of cola-induced hypokalaemia has not been determined and may vary in different patients.
"However in most of the cases we looked at for our review, caffeine intoxication was thought to play the most important role.
"This has been borne out by case studies that focus on other products that contain high levels of caffeine but no glucose or fructose."
Despite this, he warned that caffeine free cola products could also cause hypokalaemia because the fructose they contain can cause diarrhoea.
"We believe that further studies are needed to establish how much is too much when it comes to the daily consumption of cola drinks."
Excessive consumption has already been linked with obesity, diabetes and tooth and bone problems.
A spokeswoman from the British Soft Drinks Association said: "The examples used in this paper by the IJCP are all very extreme cases - moderate consumption of cola drinks is completely safe and people can continue to enjoy such drinks as part of a balanced diet and active lifestyle.
"The soft drinks industry is committed to encouraging responsible consumption of all its products. Nutrition labelling is included on pack so people can make an informed choice about the products they are drinking."_____________________________________________________________
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source: bbc uk