CCK (26-31) (sulfated) is primarily used in research to study the role of cholecystokinin in the central nervous system and gastrointestinal tract. It helps in understanding its effects on appetite regulation, anxiety, and pain modulation. The sulfated form is particularly significant as it mimics the natural bioactive form of CCK, making it valuable for investigating receptor binding and signaling pathways. Additionally, it is utilized in experiments exploring its potential therapeutic applications for disorders like obesity, anxiety, and gastrointestinal motility issues.