Diet Coke
Diet Coke does not use a modified form of the Coca-Cola recipe, but instead an entirely different formula. The controversial New Coke, introduced in 1985, used a version of the Diet Coke recipe that contained high fructose corn syrup and had a slightly different balance of ingredients. In 2004, Coca-Cola introduced Coca-Cola C2, which it claims tastes much closer to Coca-Cola but contains half the carbohydrates. In 2005, the company introduced Coca-Cola Zero (replaced by "Coca-Cola Zero Sugar" in 2017), a sugar-free variation of regular Coca-Cola.
New Coke
The sweeter cola overwhelmingly beat both regular Coke and Pepsi in taste tests, surveys, and focus groups. Asked if they would buy and drink the product if it "were" Coca-Cola, most testers said they would, although it would take some getting used to. About 10-12% of testers felt angry and alienated at the thought, and said they might stop drinking Coke altogether. Their presence in focus groups tended to negatively skew results as they exerted indirect peer pressure on other participants.