Cholecystokinin (CCK), also called pancreozymin, is a peptide hormone discovered in the small intestine. Together with secretin and gastrin, it constitutes the classical gut hormone triad.
- As a gastrointestinal hormone, CCK is secreted into the blood following ingestion of a meal and plays a critical role in the ingestion, absorption, intestinal motility, satiety signaling, inhibition of gastric acid secretion and digestion of food.
- Ingested protein and fat are potent stimulants of CCK secretion. CCK induces the gall bladder to contract and eject bile into the intestine.
- It also regulates pancreatic enzyme secretion and growth.
- It is known to induce growth of the exocrine pancreas and to stimulate insulin secretion.
-  A transmitter in central and intestinal neurons, CCK is the most abundant neuropeptide in the human brain. This peptide also induces panic attacks. The panicogenic effects of cholecystokinin-tetrapeptide are antagonized by a central cholecystokinin receptor antagonist. -  
-  ProCCK is expressed in certain neuroendocrine tumors and sarcomas, and the secretion of CCK is impaired in celiac disease and bulimia nervosa.
-  Caerulein is a decapeptide analog of the potent pancreatic secretagogue, cholecystokinin. It stimulates gastric, biliary and pancreatic secretion. In mice, caerulein injections cause acute pancreatitis.