What Is Ipamorelin? The Peptide Explained

In plain English

So, what is ipamorelin peptide? It is a man-made chain of five amino acids — the building blocks of proteins — designed in the 1990s to nudge the body into releasing its own growth hormone. Think of growth hormone release as a doorbell: ipamorelin presses one specific button, the ghrelin receptor, and a pulse of growth hormone answers. Its claim to fame is precision. Earlier peptides that pressed the same button also set off two unwanted alarms — the stress hormone cortisol and the hormone prolactin. Ipamorelin presses the growth-hormone button while barely touching those two, even at very high doses ^[1]. It is wholly synthetic; your body does not make it. It is not an approved medicine, and the only human efficacy trial it ran did not succeed ^[3]. Below, the structure and the science — kept readable.

The molecule, named precisely

Ipamorelin's sequence is Aib-His-D-2-Nal-D-Phe-Lys-NH2 — a pentapeptide (a peptide of exactly five amino acids). Two of its components are deliberately unusual. Position one is Aib (alpha-aminoisobutyric acid), a non-natural amino acid that makes the peptide harder for enzymes to chew up; positions three and four use mirror-image D-form amino acids that add the same protease resistance. The chemistry is durable by design.

It carries the development code NNC 26-0161, the molecular formula C38H49N9O5, a molecular weight near 712 daltons, and CAS number 170851-70-4. It was derived from an earlier peptide, GHRP-1, by removing a central two-amino-acid segment — a small edit that produced a large gain in selectivity. The compound is supplied for research as a freeze-dried (lyophilized) powder, either as the free base or the acetate salt.

Why selectivity is the headline

The single most important fact about ipamorelin is what it leaves alone. In the 1998 characterisation, it released growth hormone potently in three models — rat pituitary cells, anaesthetised rats, and conscious pigs — at potency comparable to GHRP-6, yet did not raise ACTH or cortisol beyond the baseline seen with growth-hormone-releasing hormone, even past 200-fold its active dose ^[1]. Prolactin stayed quiet too.

That is unusual. Most molecules that hit the ghrelin receptor hard drag other pituitary hormones up with them. Ipamorelin is the one that learned to fire on a single channel. In the language of pharmacology, that narrow, predictable action is selectivity — and it is the reason ipamorelin became, by its authors' description, the first highly selective growth hormone secretagogue.

Where ipamorelin sits among the peptides

Ipamorelin belongs to the GHRP family — growth-hormone-releasing peptides that work through the ghrelin receptor. That makes it a cousin of GHRP-2 and GHRP-6, and a complement (not a copy) of the GHRH analogs such as sermorelin, tesamorelin, and CJC-1295, which press a different button entirely.

This matters for anyone who has seen ipamorelin sold as half of a pair. The popular CJC-1295 combination puts a steady GHRH-style signal next to ipamorelin's sharp ghrelin-receptor pulse; because the two pathways are independent, a review of the whole peptide class shows their growth-hormone effects add together and resist the brakes (glucose, fatty acids, somatostatin) that blunt GHRH alone ^[11]. The science of that pairing — and how ipamorelin differs from sermorelin and tesamorelin — is laid out on the Ipamorelin research page.