Caffeine is used to addict consumers to pop, not to enhance flavour. That's the finding of researchers at Johns Hopkins University in Chicago.

The study found most people can't taste the difference between caffeinated and non-caffeinated drinks. Only 8 per cent of a group of 25 people noticed the difference.

The rest didn't notice a difference until the amount of caffeine added was beyond the accepted levels approved by the American Food and Drug Administration.

The study was published by the American Medical Association in Archives of Family Medicine.

According to the study, about 70 per cent of soft drinks in North America contain caffeine.

The study is being blasted by people in the soft drink industry. A trade group representing soft drink producers said the study was poorly conducted and designed. It also said the conclusions are irresponsible and not based on science.

According to the study, soft drink consumption has doubled since 1975 and more pop is drunk than water.

This controversy is not new. In 1981 the American Food and Drug Administration called for caffeine to be eliminated from cola drinks. The industry responded by saying caffeine was used to enhance flavour, not to addict consumers.