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.
Consumer neuroscience
A study by McClure et al. investigated the difference in branding between Coca-Cola and Pepsi. The study found that when the two drinks were tasted blind there was no difference in consumer preference between the brands. Both drinks produced equal activation in the ventromedial prefrontal cortex, which is thought to be activated because the taste is rewarding. When the subjects were informed of the brand names the consumers preferred Coke, and only Coke activated the ventromedial prefrontal cortex, suggesting that drinking the Coke brand is rewarding beyond simply the taste itself. More subjects preferred Coke when they knew it was Coke than when the taste testing was anonymous, which demonstrates the power of branding to influence consumer behavior. There was also significant activation in the hippocampus and dorsolateral prefrontal cortex when subjects knew they were drinking Coke. These brain structures are known to play a role in memory and recollection, which indicates they are helping the subjects to connect their present drinking experience to previous brand associations. The study proposes that there are two separate processes contributing to consumer decision making: the ventromedial prefrontal cortex responds to sensory inputs and the hippocampus and dorsolateral prefrontal cortex recall previous associations to cultural information. According to the results of this study, the Coke brand has much more firmly established itself as a rewarding experience.