Research Chemical Designation & Liability
Compounds indexed in the MinMaxMuscle archive are strictly for laboratory research and development. They are NOT approved for human consumption. Theoretical dosing data is aggregated from clinical literature and must not be construed as medical instruction. Professional medical consultation is mandatory prior to any research application.
Ghrelin
Growth Hormone Secretagogues
Molecular Dossier
- Rank Index: 77
- Status: Research Only
- What does this mean?
- Molecular Structure: MW: 3370.9 Da | 28 AA | CAS: 258279-04-8 | Sequence: GSSFLSPEHQRVQQRKESKKPPAKLQPR | Key modification: Ser3 octanoylation
About Ghrelin
Ghrelin is the endogenous 28-amino acid "hunger hormone" discovered in 1999, produced primarily by X/A-like enteroendocrine cells in the gastric fundus. It is the only known circulating orexigenic (appetite-stimulating) peptide and the endogenous ligand for the growth hormone secretagogue receptor (GHSR-1a) — the same receptor targeted by synthetic peptides like GHRP-2, GHRP-6, hexarelin, and ipamorelin. Circulating ghrelin rises sharply before meals and falls postprandially, acting as a key peripheral signal to the hypothalamus that drives hunger and meal initiation. Beyond appetite, ghrelin stimulates pulsatile growth hormone release from the pituitary in synergy with GHRH, explaining much of the GH-releasing activity of synthetic ghrelin mimetics. The native acylated form (octanoylated at Ser3) is required for GHSR-1a activity; des-acyl ghrelin is inactive at GHSR but has independent metabolic effects via unknown receptors. Research areas include: obesity pharmacology (anti-ghrelin antibodies and vaccines to reduce hunger), cancer cachexia and wasting disease treatment (ghrelin administration to stimulate appetite), cardiac effects (positive inotropic and vasodilatory properties), and the gut-brain axis. MK-677 (ibutamoren) is an orally bioavailable, non-peptide ghrelin mimetic currently the most practical research proxy for sustained ghrelin receptor activation. Understanding endogenous ghrelin dynamics is foundational for interpreting data on all GHRP-class peptides.
Clinical Focus
Endogenous GH Secretagogue, Appetite Regulation, Metabolic Signaling
Archival Aliases
Growth hormone secretagogue, Motilin-related peptide, Acyl ghrelin
Frequently Asked Questions
What is the natural pulsatility pattern of ghrelin and why does it matter?
Ghrelin secretion follows a pulsatile pattern tightly linked to meal timing: plasma levels peak 1–2 hours before each meal, drop sharply within 30–60 minutes of eating, and remain low for 2–3 hours postprandially. This rhythm is driven by gastric distension, nutrient sensing, and circadian clock signals. Disrupting this pattern — through irregular eating, sleep deprivation, or caloric restriction — leads to sustained elevated ghrelin, which partly explains the increased hunger and reduced satiety that makes maintained weight loss so difficult. Synthetic GHRP protocols that continuously stimulate GHSR-1a do not recapitulate this pulsatility.
What is GHSR-1a and why is it the key target for GH secretagogues?
GHSR-1a (growth hormone secretagogue receptor type 1a) is a G-protein coupled receptor expressed at high density in the pituitary, hypothalamus, and vagal neurons. It is the endogenous receptor for ghrelin and the pharmacological target of all synthetic GHRPs (GHRP-2, GHRP-6, hexarelin, ipamorelin) and orally active mimetics like MK-677. GHSR-1a has unusually high constitutive activity even without ghrelin — approximately 50% of maximal signal — which means receptor density itself modulates GH output. Compounds that act as inverse agonists at GHSR-1a (blocking constitutive activity) have been studied as anti-obesity drugs to suppress GH-driven appetite.
How do synthetic GHRPs relate to endogenous ghrelin?
Synthetic GHRPs (GHRP-2, GHRP-6, ipamorelin, hexarelin) were developed before ghrelin was discovered. They were found empirically to release GH, and ghrelin was later identified as their endogenous counterpart. All GHRPs act at GHSR-1a, but with different selectivity profiles: GHRP-6 most closely mimics ghrelin's appetite stimulation (significant increase in hunger); ipamorelin is the most selective for GH release with minimal cortisol/prolactin side effects; hexarelin is the most potent but has the most off-target activity. Understanding native ghrelin helps explain why GHRP-6 produces such pronounced hunger — it is the closest synthetic mimic of the native ligand.
What is ghrelin's circulating half-life and why can't it be used as a drug directly?
Native acyl ghrelin (the bioactive form) has a plasma half-life of approximately 9–13 minutes in humans, due to rapid deacylation by butyrylcholinesterase and carboxylesterases, and renal clearance. This makes it impractical as a therapeutic: IV infusion studies require continuous delivery to maintain effect, and the GI side effects of sustained ghrelin elevation (nausea, gastric motility changes) limit the infusion rate. Modified ghrelin analogues with extended half-lives have been developed for research purposes, but the most clinically practical GHSR-1a agonist remains MK-677 (ibutamoren), which is orally bioavailable with a 24-hour half-life and no acyl modification requirement.
Clinical Data Matrix
| Parameter | Clinical Value |
|---|---|
| Molecular Weight | MW: 3370.9 Da | 28 AA | CAS: 258279-04-8 | Sequence: GSSFLSPEHQRVQQRKESKKPPAKLQPR | Key modification: Ser3 octanoylation |
| Primary Pathway | Growth Hormone Secretagogues |
| Research Phase | Research Only |
Clinical Pros
- Highly selective receptor modulation
- Documented efficacy in Phase II trials
- Minimal systemic cross-reactivity
Research Limitations
- Limited long-term human data
- Strict storage and reconstitution requirements
- Potential for acute homeostatic feedback loops
Community Discussion
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Data Verified: 2026-05-15