Coke and Pepsi are changing the way they make their drinks in the US to avoid putting a warning label on their packaging.
The new formula will have less 4-methylimidazole, a chemical used to give the drink its brown colour.
Health experts in California say the chemical could cause cancer if drunk in very, very large doses.
Coke said they'd change their manufacturing process, but don't think the chemical is a risk to humans.
Tests were done on mice and rats using the chemical. But you'd need to drink more than 1,000 cans of Coke or Pepsi a day to take in the same dose given to the animals in the tests.
Coke have said that they won't change the recipe for Europe, though.