Ipamorelin: The Cleanest Selective Ghrelin-Receptor Agonist
A pentapeptide GH-releasing peptide that triggers pulsatile GH release without affecting cortisol or prolactin. The selectivity profile that makes it the canonical reference compound.
Ipamorelin is a pentapeptide growth-hormone-releasing peptide (GHRP) — Aib-His-D-2-Nal-D-Phe-Lys-NH₂. Among published GHRPs, ipamorelin has the cleanest selectivity profile for the ghrelin receptor, which is why it’s become the canonical reference compound for GH-axis research.
What makes it “selective”
Earlier GHRPs (GHRP-2, GHRP-6, hexarelin) trigger growth-hormone release but also raise cortisol, prolactin, and ACTH — confounders in pure GH-axis research. Ipamorelin, in published animal and human pharmacological studies:
- Triggers pulsatile GH release at the magnitude of GHRP-6
- Does not significantly affect cortisol secretion
- Does not significantly affect prolactin
- Does not affect ACTH
For research programs studying GH-axis pharmacology without confounding stress-hormone effects, this selectivity profile is the reason ipamorelin remains the reference compound rather than the broader-acting older GHRPs.
Mechanism
Ipamorelin binds the ghrelin receptor (GHS-R1a) on pituitary somatotrophs and hypothalamic neurons. Ghrelin-receptor activation:
- Triggers GH release from pituitary somatotrophs
- Suppresses somatostatin (which normally inhibits GH release) at the hypothalamic level
The combination produces a pulsatile GH release pattern that resembles endogenous secretion more closely than continuous exogenous GH administration.
Half-life
Plasma half-life in humans is approximately 2 hours. GH release peaks within 5-15 minutes of administration and returns to baseline within ~3 hours. The pharmacokinetics support intermittent rather than continuous administration in research protocols.
Research contexts
Ipamorelin has been studied in:
- GH-axis pharmacology characterization
- Sarcopenia-related research models
- Post-surgical recovery models (where GH plays a role)
- Pediatric GH-deficiency research (clinical trials)
Clinical translation has occurred in some indications but ipamorelin is not approved for general therapeutic use.
Sourcing notes
The pentapeptide is stable in lyophilized form. Purity >98% HPLC is the reference threshold. Reference-grade material should ship with mass-spec confirmation matching theoretical molecular weight (711 Da). The peptide is hygroscopic — store lyophilized at -20°C, reconstitute in bacteriostatic water for the standard 28-day refrigerated window.
Related notes
Continue reading.
A Brief History of Peptide Synthesis
From solution-phase to solid-phase to the modern automated synthesizer — how research-peptide manufacturing actually got to the point where you can order a 39-amino-acid molecule for under $200.
Reading a Certificate of Analysis: A Field Guide
Every legitimate research-peptide supplier publishes a COA per lot. Here's what each section actually means — and which numbers you should trust.
HPLC Purity: What the Chromatogram Actually Tells You
A purity percentage with no chromatogram is roughly worthless. Here's how to read the underlying data and what each peak means.