High-energy drinks containing large amounts of caffeine will require new labelling under rules announced by the European Commission.
Too much caffeine could be a health risk, but its use as a flavouring does not currently have to be mentioned in ingredients listed on packaging.
In future, drinks which contain more than 150 milligrams of caffeine per litre will have to be prominently labelled as having a "high caffeine content".
Normal cola drinks will not be affected, neither will drinks based on tea or coffee - as long as the name of the drink makes clear it has been made from tea or coffee.
New labelling for quinine, used as flavouring in soft drinks such as tonic water, will also have to be specifically labelled. The new rules are due in force by July 2004.
A Commission spokeswoman said: "While consumption of moderate levels of both substances is unlikely to pose any health risks for most consumers, other may suffer adverse effects - in some cases even if consumed in very small quantities.
"The new rules will alert consumers to the presence of these substances and, in the case of caffeine, indicate where the level exceeds a certain limit."
At the moment, she added, even where caffeine is listed as an ingredient, there is no legal requirement to indicate whether the level is high.
"The new rules will address these shortcomings and harmonise the differing national rules currently applying to these substances across the European Union thus facilitating intra-Community trade in the products concerned," said the spokeswoman.
"Putting the term 'high caffeine content' and the amount in the same field of vision as the name of the product will alert consumers to unexpectedly high caffeine levels in certain soft drinks especially in most of the so-called high energy drinks."