Ipamorelin

Molecular identity

Sequence

Aib-His-D-2-Nal-D-Phe-Lys-NH2

Formula

C38H49N9O5

Molecular weight

711.9 g/mol

CAS

170851-70-4

PubChem CID

9831659

What it acts on

• GHRP-type receptor on pituitary somatotrophs — pharmacological profiling with GHRP and GHRH antagonists in the founding paper placed the growth-hormone response at a GHRP-like receptor, not at the GHRH receptor. The site is characterised there pharmacologically only; the ghrelin-receptor designation GHS-R1a is later nomenclature and appears in none of the sources cited here.
• Growth-hormone release from somatotrophs — in primary rat pituitary cell culture, and again in anaesthetised rats and conscious swine, GH release was similar to GHRP-6 in potency and efficacy.
• Hypothalamic–pituitary–adrenal axis — the defining reported property is a negative one: where GHRP-6 and GHRP-2 raised ACTH and cortisol, this compound left both at levels not significantly different from GHRH stimulation, even at exposures far above those needed for GH release.
• Other anterior-pituitary axes — in swine, none of the secretagogues tested altered plasma FSH, LH, prolactin or TSH, which is the basis of the paper's selectivity claim.
• Downstream GH→IGF-1 signalling with satellite-cell repair — a 2026 orthopaedic review groups the compound with other GH secretagogues on this axis, but that is the review's mechanistic framing rather than a measured endpoint.

What the studies report

Each item below summarises the paper it is numbered to, written from that paper's own abstract. The badge says how the evidence was produced.

1. 1.
   animal modelEur J Endocrinol (1998)

   The founding pharmacology paper (1998). It describes the compound as a pentapeptide identified within a series built without the central Ala-Trp dipeptide of GHRP-1 and characterises it across three systems: primary rat pituitary cell culture, pentobarbital-anaesthetised rats and conscious swine. In each, GH release was similar to GHRP-6 in potency and efficacy, and profiling with GHRP and GHRH antagonists located the effect at a GHRP-like receptor. The selectivity result is the paper's own headline: GHRP-6 and GHRP-2 raised ACTH and cortisol, whereas with ipamorelin both stayed at levels not significantly different from those observed after GHRH stimulation, and none of the secretagogues tested altered FSH, LH, prolactin or TSH. The authors close by proposing it as a candidate for future clinical development — that is, no human data are reported here.

2. 2.
   reviewJ Am Acad Orthop Surg Glob Res Rev (2026)

   A 2026 review of therapeutic peptides in orthopaedics, organised around signalling networks — PI3K/Akt, mTOR, MAPK, TGF-β and AMPK. It groups ipamorelin with CJC-1295, tesamorelin, sermorelin and AOD-9604 as growth-hormone secretagogues said to act through IGF-1 signalling and satellite-cell repair. This is a mechanistic synthesis rather than new data, and the authors state plainly that although preclinical studies are promising, clinical trials are currently lacking.

3. 3.
   reviewAm J Sports Med (2026)

   A narrative review written for orthopaedic and sports-medicine physicians, drawing on a PubMed search of biochemical and clinical studies of the most heavily marketed injectable peptides. Ipamorelin appears in it only in combination with CJC-1295: that pairing is reported to have significantly improved maximum tetanic tension in murine models of glucocorticoid-induced muscle loss, and the review states directly that the finding is confined to animal studies. Its overall conclusion is that indications, dosing, frequency and duration remain unknown and that substantial safety and efficacy research is needed before any recommendation can be made.

4. 4.
   reviewSports Med (2026)

   A 2026 narrative review in Sports Med covering both approved and unapproved peptides marketed direct to patients, ipamorelin among the compounds surveyed. It describes a parallel "gray market" of unapproved compounds operating largely outside regulatory oversight — the abstract does not state on which side of that line each listed compound falls — and concludes that while many such peptides show favourable tissue-repair and metabolic outcomes in animal models, rigorous human safety data are scarce and there is potential for serious harm. The review also treats the placebo effect as a mediator of reported peptide efficacy and discusses how social media amplifies it.

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