Cadbury said that, from this month, its Seven Up drink would be made with only five 100 per cent natural ingredients: filtered carbonated water, high fructose corn syrup, natural citric acid, natural flavours and natural potassium citrate.
Soft drinks firms have been under pressure over the last couple of years from a consumer shift away from artificial, sugar-laden sodas.
The Seven Up reformulation may help Cadbury differentiate the brand from others on a stagnant US carbonated drinks market, which analysts believe holds few growth opportunities.
Randy Gier, marketing head for Cadbury Schweppes Americas Beverages, said: "By removing all the artificial ingredients, 7UP is remaining true to its roots as the 'Uncola' - an alternative to other carbonated soft drinks on the market."
The Seven Up re-launch, which coincides with the brand's 77th birthday, also follows promising reports on the US natural products market.
The natural soda market grew by almost 15 per cent between May 2004 and May 2005, according to market research group SPINS.
Another research firm, IRI, said in January this year that 94 per cent of American households had bought a natural product, and predicted the sector would show high single-digit growth over the next five years.
Debate, however, has raged over what '100 per cent natural' should mean when printed on a product label.
The Food and Drug Administration (FDA) has set no official guidelines on the definition of natural ingredients, although advised last year that natural ingredients should be derived from "natural sources", such as corn or soybeans.
Some industry representatives told the FDA in the 1990s that the label '100 per cent natural' should be banned because it was generally false and misleading to consumers.
The US Natural Ingredient Resource Center devised its own definition of natural ingredients last year, after inviting comments from the food industry.
It said natural ingredients should be present in or produced by nature, produced using "minimal processing" (using methods possible in a household kitchen or on a farm), and "directly extracted" using simple methods.
Cadbury Schweppes was unavailable for comment on the issue.
Artifical ingredients that Cadbury has removed from Seven Up include the preservative, calcium disodium EDTA, while it has also nearly halved sodium content.
The continuing presence of high fructose corn syrup is, however, likely to leave Seven Up open to criticism from health campaigners.
Some studies and nutritionists have linked the ingredient to America's obesity crisis and growing diabetes rate. Soft drinks were identified as Americans' principal source of high fructose corn syrup in 2001.