Peptide Schedule
Cholecystokinin (CCK-8)8 residuesDYMGWMDFEach bubble = one amino acid. Size = residue mass. Color = chemical class.Cholecystokinin (CCK-8)
Benefits
About Cholecystokinin (CCK-8)
Cholecystokinin (CCK-8) is a sulfated octapeptide fragment of the 33-amino-acid gut hormone cholecystokinin, first isolated from porcine intestinal mucosa in the 1960s. It is the most bioactive circulating form of CCK and plays a central role in the gut-brain axis, acting as a primary short-term satiety signal released by I-cells in the duodenal and jejunal mucosa in response to dietary fat and protein. CCK-8 exerts its physiological effects through two receptor subtypes: CCK1 receptors (formerly CCK-A), which predominate in the gastrointestinal tract, pancreas, and vagal afferent neurons, and CCK2 receptors (formerly CCK-B), which are widely distributed in the central nervous system. Activation of peripheral CCK1 receptors stimulates gallbladder contraction, relaxation of the sphincter of Oddi, secretion of pancreatic digestive enzymes, and inhibition of gastric emptying. Vagal CCK1 receptor activation transmits satiety signals to the nucleus tractus solitarius in the brainstem, reducing meal size and promoting meal termination. In the central nervous system, CCK-8 acts as a neuromodulator with roles in anxiety, panic responses, pain modulation, memory, and dopaminergic neurotransmission. The related fragment CCK-4 is a well-established panicogenic agent in human research, and elevated brain CCK levels are implicated in anxiety and panic disorders. The synthetic C-terminal octapeptide of CCK, known as sincalide (marketed as Kinevac), received FDA approval in 1976 as a diagnostic agent for assessing gallbladder ejection fraction and stimulating pancreatic secretion during imaging studies. Native CCK-8 remains a critical research tool for studying appetite regulation, gastrointestinal motility, and neuropeptide signaling. Its rapid enzymatic degradation in plasma (half-life of 2-5 minutes) has spurred development of protease-resistant, long-acting CCK1 receptor agonists as potential anti-obesity therapeutics.
Who Should Consider Cholecystokinin (CCK-8)
- Appetite and satiety researchers
- Gastrointestinal motility investigators
- Obesity and metabolic disorder researchers
- Neuroscience researchers studying anxiety and panic
- Gastroenterologists evaluating gallbladder function
- Pain and nociception researchers
How Cholecystokinin (CCK-8) Works
CCK-8 acts through two G-protein-coupled receptor subtypes: CCK1 (predominantly peripheral) and CCK2 (predominantly central). Upon binding, both receptors activate Gq/11 signaling cascades, stimulating phospholipase C to generate inositol trisphosphate (IP3) and diacylglycerol (DAG). IP3 triggers intracellular calcium release from the endoplasmic reticulum, while DAG activates protein kinase C (PKC). In pancreatic acinar cells, this calcium-dependent pathway drives exocytosis of zymogen granules containing digestive enzymes. In gallbladder smooth muscle, the same signaling cascade produces contraction and bile ejection. CCK-8 also activates adenylyl cyclase via Gs coupling in certain tissues, increasing cAMP and activating protein kinase A (PKA). A critical satiety pathway involves CCK1 receptor activation on vagal afferent nerve endings in the gastric and duodenal mucosa. This triggers action potentials transmitted via the vagus nerve to the nucleus tractus solitarius (NTS) in the brainstem, which relays to hypothalamic feeding centers to suppress appetite and terminate meals. CCK-8 also slows gastric emptying through both vagal and direct smooth muscle mechanisms, prolonging nutrient contact with absorptive epithelium. In the central nervous system, CCK-8 modulates dopaminergic, serotonergic, and GABAergic neurotransmission, contributing to its roles in anxiety, pain perception, and reward circuitry.
What to Expect
Onset of gallbladder contraction and initial satiety signaling following IV administration
Peak gallbladder contraction (40-70% reduction in volume); maximal suppression of appetite and gastric emptying
Effects begin to wane as CCK-8 is rapidly cleared from plasma; meal-related satiety persists via downstream neural signaling
Return to baseline gastrointestinal motility; CCK levels normalize to pre-administration values
Dosing Protocol
| Level | Dose / Injection | Frequency |
|---|---|---|
| Beginner | 1mcg | Daily |
| Moderate | 2mcg | Daily |
| Aggressive | 4mcg | 2x Daily |
Note: Cholecystokinin-8 (CCK-8) is the sulfated octapeptide form of the endogenous gut-brain hormone cholecystokinin. It is one of the most potent naturally occurring satiety signals in mammalian physiology. CCK-8 binds both CCK1 (peripheral) and CCK2 (central) G-protein-coupled receptors, triggering gallbladder contraction, pancreatic enzyme secretion, gastric emptying delay, and vagal afferent satiety signaling. In clinical medicine, its synthetic analog sincalide (Kinevac) is FDA-approved as a diagnostic agent for gallbladder function testing. Research interest in CCK-8 extends to appetite regulation, anxiety modulation, pain processing, and neuroprotection. However, its extremely short plasma half-life of 2-5 minutes limits therapeutic utility, driving development of longer-acting CCK1-selective analogs for obesity treatment. All investigational use of native CCK-8 remains research-only.
How to Inject Cholecystokinin (CCK-8)
CCK-8 is supplied as a lyophilized powder and must be reconstituted with bacteriostatic water before use. For intravenous research protocols, doses of 0.02-0.04 mcg/kg are administered as a slow bolus over 30-60 seconds or as a diluted infusion over 30-60 minutes to minimize gastrointestinal side effects. Subcutaneous administration is used in some research settings, though bioavailability is lower and onset delayed compared to IV. The peptide should be injected 15-30 minutes before meals when investigating satiety effects. Rapid IV bolus injection increases the risk of nausea, abdominal cramping, and vasovagal responses; slow infusion is strongly preferred. Due to the extremely short half-life, timing of administration relative to meals is critical. Reconstituted solution should be clear and colorless; discard if particulates or discoloration are observed. Store reconstituted vials at 2-8°C and use within 7 days.
Cycling Protocol
Due to its extremely short half-life and rapid clearance, CCK-8 does not accumulate significantly and tachyphylaxis is the primary concern with continuous dosing. Research protocols typically employ intermittent administration around meals rather than continuous cycling. Extended use may lead to CCK1 receptor desensitization, supporting periodic breaks in administration.
Pharmacokinetics
Source: Hopman et al. Gut 1990; PMID 2378793 — CCK-33 elimination t½ = 4.2 min IV in humans; CCK-8 cleared even faster (~2-3 min)
Loading the interactive decay curve.
Side Effects
The most commonly reported side effects of exogenous CCK-8 administration in human studies are abdominal discomfort or pain and nausea, occurring in over 20% of subjects at diagnostic doses. At higher or bolus doses, gastrointestinal adverse effects become more pronounced, including abdominal cramping, vomiting, diarrhea, and a transient urge to defecate due to increased intestinal motility. Dizziness, flushing, and diaphoresis have been reported, likely related to vasovagal activation. Hypersensitivity reactions including anaphylaxis and anaphylactic shock have been documented in post-marketing surveillance of sincalide, attributed in part to the sodium metabisulfite preservative. Neurological effects are rare but include headache and, very rarely, seizures. Bradycardia and transient hypotension can occur with rapid intravenous bolus administration. Most side effects are dose-dependent, transient, and resolve within minutes due to the peptide's extremely short half-life.
Contraindications
- Intestinal obstruction (CCK-8 increases intestinal motility and could worsen obstruction)
- Known hypersensitivity to sincalide or sulfite-containing preparations
- Gallbladder stones (risk of stone dislodgement into cystic or common bile duct)
- Pregnancy (risk of preterm labor and spontaneous abortion due to smooth muscle stimulation)
- Active acute pancreatitis (CCK-8 stimulates pancreatic secretion and could exacerbate inflammation)
Drug Interactions
- Opioid analgesics (morphine, fentanyl) — inhibit gallbladder contraction and oppose CCK-8 effects on biliary motility for up to 18 hours
- Anticholinergic agents (atropine, glycopyrrolate) — may attenuate CCK-8-mediated gallbladder contraction and gastrointestinal motility
- CCK receptor antagonists (loxiglumide, devazepide) — directly block CCK1/CCK2 receptor activation and abolish CCK-8 effects
- Somatostatin analogs (octreotide) — inhibit CCK release and may blunt downstream GI responses
Storage & Stability
Molecular Profile
Related Peptides
References
- Biochemistry, Cholecystokinin (StatPearls 2023)Review
- Gastrointestinal satiety signals II. Cholecystokinin (Am J Physiol Gastrointest Liver Physiol 2004)Review
- Dose-dependent effects of cholecystokinin-8 on antropyloroduodenal motility, gastrointestinal hormones, appetite, and energy intake in healthy men (Am J Physiol Endocrinol Metab 2009)PubMed 18957613
- Lack of effect of the specific cholecystokinin receptor antagonist loxiglumide on cholecystokinin clearance from plasma in man (Gut 1990)PubMed 2378793
- KINEVAC (sincalide) FDA Prescribing InformationFDA Label