Cholecystokinin is a hormone which when injected in human body _____.

Concept: Appetite and food intake are governed by opposing gut/adipose hormones — orexigenic (hunger) hormones such as ghrelin signal the brain to eat, while anorexigenic (satiety) hormones such as cholecystokinin (CCK), leptin, and peptide YY signal fullness and suppress further intake.

Application: Cholecystokinin is secreted by I-cells in the duodenal and jejunal mucosa when fat and protein arrive from the stomach. Locally it slows gastric emptying and stimulates gallbladder contraction and pancreatic enzyme release; centrally it signals through vagal afferent fibres to the hypothalamus, producing satiety. So when cholecystokinin is injected into the body, this satiety signalling reduces the drive to eat — it decreases appetite.

Cross-check: This places cholecystokinin opposite ghrelin, which is released by an empty stomach and increases appetite — ruling out any option describing an appetite rise. In its standard, well-characterized human/peripheral role, cholecystokinin's satiety signalling runs through vagal afferents to the hypothalamus; a reduced-thirst effect from ordinary cholecystokinin injection is not part of that established, exam-standard profile (thirst is primarily tracked to plasma-osmolality sensing via osmoreceptors and vasopressin/ADH), so an option that extends cholecystokinin's action to thirst goes beyond its standard characterization.

Hence, cholecystokinin, when injected in the human body, decreases appetite.