Exotic plant extracts routinely added to high-energy soft drinks should be more strictly controlled, Britain's Food Standards Agency has warned. The agency, set up last year to protect consumers, is calling on the European Commission to investigate the rapidly expanding use of medicinal herbs such as ginseng, guarana, and echinacea as stimulants and flavourings by the £178m energy drinks sector, following a crackdown on "health" drinks in the US.

The agency's proposals would force the makers of drinks such as Purdey's, Solstis, Lipovitan B3 and Pete and Johnny's to prove that such herbs are safe. The companies may be forced to cut the level of potentially risky ingredients or print health warnings on labels. Red Bull, which has 70 per cent of the British market, has already been accused by the Advertising Standards Authority and the Consumers Association of misleading people by claiming that it "vitalises mind and body".

Stimulant drinks are now the biggest growth area in Britain's soft drinks industry, with sales, spurred by club culture, rising by 17 per cent last year. But the industry was shaken when the US Food and Drug Administration wrote to manufacturers telling them their use of the herbs was illegal. American law says firms must show that all ingredients are safe for use in foods, even if they are already approved for medical use. The companies contacted by the FDA will now have to produce scientific evidence that their products are safe.

The crackdown affects products sold in the American market by drinks giants such as Pepsi and Cadbury-Schweppes, which recently bought Snapple, a fruit juice brand which in the US features guarana, echinacea and ginseng.

The US controversy has highlighted a loophole in British and European laws on the use of medicinal herbs in drinks. Although traditional herbs used for medical purposes are checked by the Medicines Control Agency, and labelled with safety guidelines, the same plants can be used in drinks without testing if they have been generally used for years. This means they escape strict EU regulations which require testing for novel or new ingredients.

While there is no scientific evidence that energy drinks are dangerous, health experts and consumer groups fear consumers could take unsafe levels of some herbs, or be confused about their health value.

Experts warn that guarana, a South American bean, should be used cautiously by people with heart problems, and pregnant or breast-feeding women, because it contains high levels of caffeine. Ginseng, used to aid alertness and stress-resistance, is regarded as safe, but should be avoided during colds or bouts of flu. Echinacea, a remedy for coughs and infections, should not be taken constantly because it could harm the immune system.

Manufacturers insist their products are safe, but have contradictory views about using them. Pete and Johnny's, which sells four fruit drinks with a different herb in each, said it will not mix plants because each herb has a particular function. GlaxoSmithKline puts both guarana and ginseng in its Solstis Lucozade drink, but claims they are flavourings not energy enhancers.

The agency said that while it had no evidence of ill-effects caused by these herbs it is concerned that existing EU food safety regulations are too lax. The agency is pressing David Byrne, the public health commissioner, to extend an EU inquiry into the use of vitamins and minerals in food supplements to cover energy drinks.

Harry Cragoe, the chief executive of Pete and Johnny's, said: "We know an enormous number of people believe herbal remedies play an active role in their lifestyles and we're providing products to fulfil that need."

Additional research by Ivan Zenovic