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
Some Coca-Cola executives had quietly been arguing for a reintroduction of the old formula as early as May. By mid June, when soft drink sales usually start to rise, the numbers showed that new Coke was leveling among consumers. Executives feared social peer pressure was now affecting their bottom line. Some consumers even began trying to obtain "old" Coke from overseas, where the new formula had not yet been introduced, as domestic stocks of the old drink were exhausted. Over the course of the month, Coca-Cola's chemists also quietly reduced the acidity level of the new formula, hoping to assuage complaints about the flavor and allow its sweetness to be better perceived (advertisements pointing to this change were prepared, but never used).