Caffeine is a well-known stimulant added as an ingredient to various carbonated soft drinks, but which drink contains the most, and how can consumers know? A study in the Journal of Food Science used high-performance liquid chromatography to analyze the caffeine contents of 56 national-brand and 75 private-label store brand carbonated beverages. Caffeine contents ranged from 4.9 mg/12 oz (IGA Cola) to 74 mg/12 oz (Vault Zero). Some of the more common national-brand carbonated beverages analyzed in this study were Coca-Cola (33.9 mg/12 oz), Diet Coke (46.3 mg/12 oz), Pepsi (38.9 mg/12 oz), Diet Pepsi (36.7 mg/12 oz), Dr Pepper (42.6 mg/12 oz), Diet Dr Pepper (44.1 mg/12 oz), Mountain Dew (54.8 mg/12 oz), and Diet Mountain Dew (55.2 mg/12 oz). The authors found that store-brand beverages generally contained less caffeine, and they also suggest that consumers would benefit from having the actual caffeine content labeled on the beverage.