Ghrelin

What it is

ghrelin is a 28-amino-acid peptide hormone discovered in 1999 as the endogenous ligand for the growth hormone secretagogue receptor (GHSR, specifically the GHS-R1a isoform). It is primarily secreted by oxyntic (X/A-like) cells of the gastric fundus mucosa, with smaller amounts produced in the hypothalamus, pituitary, and other tissues. Ghrelin is distinguished by a unique post-translational octanoylation: the enzyme ghrelin-O-acyltransferase (GOAT) attaches an n-octanoyl (C8) fatty acid group to the serine residue at position 3, and this acylation is essential for GHS-R1a binding and the principal hormonal activities. Unacylated (desacyl) ghrelin circulates at higher concentrations but does not activate GHS-R1a at physiological concentrations. GHS-R1a is a Gα(q/11)-coupled GPCR expressed on pituitary somatotrophs (mediating GH release), hypothalamic arcuate nucleus neurons (mediating appetite via NPY/AgRP upregulation), and widely across the brain, pancreas, adipose tissue, cardiovascular system, and immune cells. A second isoform, GHS-R1b, does not bind ghrelin independently but forms functional heterodimers with GHS-R1a that modulate signaling. Physiologically, plasma ghrelin rises preprandially, peaks just before meal initiation, and falls within 1–2 hours after eating — a pattern suggesting a role in meal initiation. Ghrelin is described as the sole circulating orexigenic hormone. Its appetite-stimulating effect is mediated in part through hypothalamic NPY and AgRP neurons. Ghrelin also promotes fat storage, reduces energy expenditure, and increases respiratory quotient. In the hippocampus, GOAT-mediated local acylation of ghrelin activates GHSR1a, upregulates cAMP and CREB phosphorylation, amplifies NMDA receptor-mediated synaptic transmission, and activates Fyn kinase — supporting adult neurogenesis and memory consolidation. In cardiac tissue, ghrelin and GHSR expression increase in diseased left ventricular tissue, suggesting a compensatory role in heart failure. A newly identified endogenous antagonist, LEAP2 (liver-expressed antimicrobial peptide 2), acts as an inverse agonist at GHS-R1a and opposes ghrelin's effects.

Class: Endogenous 28-amino-acid octanoylated peptide hormone / growth hormone secretagogue / orexigenic gut-brain hormone

What it's studied for

• Appetite stimulation and treatment of cachexia / wasting syndromes Mixed
  • Review of clinical ghrelin studies for cachexia: open-label studies in congestive heart failure, COPD, and cancer patients demonstrated repeated ghrelin dosing improved appetite, body composition, muscle preservation, and functional capacity. Ghrelin identified as the only circulating hormone that stimulates appetite i PMID 21635929 Akamizu T et al. Peptides. 2011.
  • Review of emerging anticatabolic ghrelin therapy: pilot clinical studies in heart failure and COPD showed repeated ghrelin dosing improved appetite, body composition, muscle preservation, and exercise capacity. Cancer patients showed marked increases in energy intake. Authors note positive signals from multiple clinica PMID 17414495 Akamizu T et al. Curr Opin Clin Nutr Metab Care. 2007.
  • Comprehensive review: ghrelin is the sole circulating orexigenic hormone. Reviews translational pharmacology covering metabolic disorders, GI disease, neurodegeneration, chronic pain, psychiatric disorders, and wasting syndromes. Notes that short plasma half-life (due to acyl modification lability) is the primary deliv PMID 41932551 Bukhari SMS et al. Toxicol Appl Pharmacol. 2026.
• Growth hormone secretion stimulation Mixed
  • Review: exogenous ghrelin potently stimulates pituitary GH release in humans, partly dependent on endogenous GHRH. GHS-R1a on pituitary somatotrophs mediates this effect. Endogenous ghrelin's role in physiological GH control remains uncertain — ghrelin-deficient animals grow normally, suggesting redundancy. Chronic ghr PMID 17195943 Dimaraki EV et al. Rev Endocr Metab Disord. 2006.
  • Review: ghrelin requires octanoyl modification on serine-3 for GHSR activation. Acts synergistically with GHRH to amplify GH pulses while inhibiting somatostatin. Nesfatin counteracts ghrelin's GH-stimulating effect via cAMP/PKA/CREB pathway downregulation. Documents complex regulatory network in which ghrelin is one o PMID 33776931 Devesa J et al. Front Endocrinol. 2021.
• Gastrointestinal motility and gastric emptying in heart failure Human RCT
  • RCT (n=29 heart failure patients with reduced ejection fraction). Acyl ghrelin infusion at 0.1 µg/kg/min for 120 min vs. placebo after 500-kcal breakfast. Treatment group: 57% showed peak paracetamol at 30 min (accelerated gastric emptying) vs. 7% placebo (P=0.004). Rapid-emptying subgroup showed increased cardiac outp PMID 41886075 Webb DL et al. Naunyn Schmiedebergs Arch Pharmacol. 2026.
• Hippocampal neurogenesis and memory/cognitive effects Animal studies only
  • Review: acyl-ghrelin promotes adult hippocampal neurogenesis and enhances memory; unacylated ghrelin inhibits these processes. The circulating acyl-ghrelin:unacylated-ghrelin ratio proposed as a critical regulator of neurogenesis and cognition. GOAT enzyme and acyl modification essential for all CNS neurogenic effects PMID 35845996 Thomas AS et al. Front Physiol. 2022.
  • Review of hippocampal ghrelin acylation: GOAT localizes at dentate granule cell layer in rodents (absent in GHSR1a KO mice). GHS-R1a activation by acylated ghrelin upregulates cAMP, CREB phosphorylation, amplifies NMDA receptor-mediated synaptic transmission, and activates Fyn kinase — establishing a mechanistic basis PMID 35180934 Isokawa M et al. Vitam Horm. 2022.
• Cardiovascular function in heart disease Mixed
  • Human cardiac tissue study (n=25 valvular disease patients + autopsy controls): GHSR-ghrelin positive correlation found only in diseased tissue; ghrelin and BNP colocalized to same intracellular compartments in both tissue types; strong correlations between GHSR, ghrelin, BNP, and SERCA2a appeared exclusively in diseas PMID 33644732 Sullivan R et al. CJC Open. 2021.

Community-reported dosing

Tier key: Research = PMID-cited study · [C] = scraped community source · [S] = model-synthesized from aggregate community reports (softer evidence). How we source.

Safety signals

• RCT in heart failure patients (n=29): acyl ghrelin infusion 0.1 µg/kg/min for 120 min was well-tolerated; no serious adverse events described in abstract. Accelerated gastric emptying and increased cardiac output observed in rapid-emptying subgroup. PMID 41886075
• Short plasma half-life due to rapid deacylation by plasma esterases — biological activity of administered acyl ghrelin diminishes rapidly in vivo. Receptor desensitization with repeated dosing is a recognized concern. PMID 41932551
• Ghrelin promotes fat storage and appetite — chronic administration promotes weight gain via orexigenic and metabolic mechanisms; appropriate monitoring of body composition warranted with extended use. PMID 17195943

Contraindications

• Obesity and metabolic syndrome — ghrelin promotes fat storage, reduces energy expenditure, and has been implicated in obesity pathophysiology; use in obese individuals may exacerbate metabolic dysfunction. PMID 27376422
• No formal contraindications established in reviewed literature for exogenous ghrelin administration. No published clinical safety guidelines for use outside controlled trial settings. Individuals with active malignancy, diabetes, or cardiovascular disease should not use without medical supervision given ghrelin's pleiotropic receptor activity across multiple organ systems. PMID 41932551