Cholecystokinin (CCK) is a hormone originally isolated from porcine intestinal mucosa and described as a linear 33-amino acid peptide containing a sulfated tyrosine, which is essential for its biological activity. It has been found in mammals in both the digestive tract and the central nervous system. Among its multiple biological functions, this hormone stimulates pancreatic exocrine secretion, gallbladder contraction, and intestine motility and may also act as a neurotransmitter/neuromodulator in the central nervous system. For CCK-4 see H-3110.

CCK-8 exhibits various gastrointestinal effects as contraction of the gallbladder and stimulation of pancreatic secretion and gastrointestinal transit. In rats, CCK-8 facilitated the uptake of leptin from peripheral circulation to cerebrospinal fluid and its access to the hypothalamus. For CCK-4 see H-3110.