// the molecule
What Is Ipamorelin? The Peptide Explained
Structure, naming, receptor, and what the molecule actually does — the identifiers in code style, the mechanism in plain words.
In plain English
So, what is ipamorelin peptide? It is a lab-made chain of five amino acids — a pentapeptide — that acts like the body's hunger hormone, ghrelin, at one specific receptor. When it docks onto that receptor on the brain's hormone gland, it triggers a short, clean burst of growth hormone, the body's own growth-and-repair signal. The word that defines it is "selective": it raises growth hormone without raising cortisol, the stress hormone that older peptides in its family pushed up as an unwanted side effect. It is wholly synthetic — your body does not make it — and it was designed in the 1990s. It has never been approved as a medicine anywhere, and almost everything known about it comes from animal studies plus two small human ones. This page explains its structure, its names, and what it does, with the technical identifiers kept exact.
Structure and sequence
Ipamorelin is a synthetic pentapeptide with the sequence Aib-His-D-2-Nal-D-Phe-Lys-NH2 [1]. It was derived from GHRP-1 by removing the central Ala-Trp dipeptide, and two design choices give it durability: alpha-aminoisobutyric acid (Aib, a non-natural amino acid) at position 1, and D-form amino acids (D-2-naphthylalanine and D-phenylalanine) that resist the enzymes which would otherwise chew up a normal peptide [1]. Its molecular formula is C38H49N9O5 with a molecular weight near 711.85 Da, and its CAS number is 170851-70-4. The free base corresponds to PubChem CID 9831659; the acetate salt is a distinct entity. None of those identifiers describe a drug product — they describe a research chemical.
Names and codes
Ipamorelin travels under several labels. Its development code is NNC 26-0161, assigned by the pharmaceutical company that discovered it; it is sometimes written as ipamorelin acetate when supplied as the salt. Functionally it sits in the GHRP class — growth-hormone-releasing peptides — which act on the ghrelin receptor, as distinct from GHRH analogs (such as CJC-1295, sermorelin, and tesamorelin) that act on the separate growth-hormone-releasing-hormone receptor [1]. Knowing which class a compound belongs to is the fastest way to understand what it does and what it pairs with, a distinction drawn out on the Ipamorelin research page.
What it does, mechanistically
Ipamorelin activates GHS-R1a — the growth hormone secretagogue receptor type 1a, better known as the ghrelin receptor — on the pituitary gland's growth-hormone-producing cells [1]. That activation opens a calcium-based signal inside the cell that releases a pulse of growth hormone. Its defining feature, established in 1998, is that it does this without meaningfully raising ACTH, cortisol, or prolactin, even far above the dose needed for growth-hormone release [1]. Downstream, growth hormone can raise IGF-1 (insulin-like growth factor 1) via the liver, though short rodent studies often show bone effects without a measurable IGF-1 rise [2] — one of the more interesting wrinkles in the ipamorelin literature.
How it differs from its own drug family
Ipamorelin belongs to the GHRP family — growth-hormone-releasing peptides — but it is the family's selective member. The earlier GHRPs (GHRP-6 and GHRP-2) release growth hormone through the same ghrelin receptor, but they also push up ACTH, cortisol, and prolactin; ipamorelin's design strips that out, releasing growth hormone potently (swine ED50 2.3 nmol/kg, comparable to GHRP-6) while leaving the stress hormones near baseline even at doses more than 200-fold higher [1]. That is the practical meaning of "first selective growth hormone secretagogue." It is a different axis from the GHRH analogs entirely: CJC-1295, sermorelin, and tesamorelin act on the growth-hormone-releasing-hormone receptor, an upstream cAMP pathway, while ipamorelin acts on the downstream ghrelin receptor's calcium pathway [1] — which is exactly why the two classes are discussed as complementary stack partners rather than substitutes.
What the research has actually measured
Knowing what ipamorelin is leads naturally to what it has been shown to do, and the answer is mostly skeletal and mostly preclinical. The defining bone result is a dose-response: subcutaneous ipamorelin at 18, 90 and 450 microg/day raised longitudinal bone growth rate in rats from 42 microm/day to 44, 50 and 52 microm/day, stepwise, with no measurable change in total IGF-1 [2]. Continuous dosing over 12 weeks raised total bone mineral content [3], and the molecule's clean growth-hormone pulse peaks about 40 minutes after a dose in humans, clearing with a roughly 2-hour half-life [6]. These are the kinds of measurements that anchor the Ipamorelin research page — concrete figures from named studies, not marketing claims. The deeper, dose-graded skeletal findings live on the ipamorelin benefits page.
What it is not
Ipamorelin is not an approved drug — it has no approved indication in any country, and its only Phase 2 trial (for postoperative ileus, slowed bowel recovery after surgery) missed its primary endpoint [7]. It is not the same thing as the CJC-1295 + ipamorelin combination; this site covers pure ipamorelin, and the combination is a separate pairing untested in humans [16]. It is not orally active in its native form — only engineered analogs achieve meaningful oral bioavailability. It is not a growth-hormone-releasing hormone (GHRH) analog like CJC-1295, sermorelin, or tesamorelin; it works through the separate ghrelin receptor [1]. And research-grade ipamorelin is not a pharmaceutical-quality product: material from unregulated suppliers has unverified purity and identity. For the honest account of reported effects and cited cautions, see the Ipamorelin effects page.