Ipamorelin

The first selective growth-hormone secretagogue: a pentapeptide ghrelin mimetic that stimulates a clean pulse of GH from the pituitary without the ACTH and cortisol spillover seen with earlier GHRPs.

What it is

Ipamorelin is a synthetic pentapeptide with the sequence Aib-His-D-2-Nal-D-Phe-Lys-NH₂. It belongs to the growth-hormone-releasing peptide (GHRP) family and acts as a selective agonist at the growth-hormone secretagogue receptor (GHS-R1a), the same receptor targeted by the endogenous hormone ghrelin. Because it mimics ghrelin at that receptor rather than acting on the GHRH receptor, it is classed as a ghrelin mimetic or GH secretagogue.

Ipamorelin was first described by Raun and colleagues at Novo Nordisk in 1998, in a paper in the European Journal of Endocrinology titled "Ipamorelin, the first selective growth hormone secretagogue." The defining feature reported in that work was its selectivity: it released GH with a potency comparable to GHRP-6, yet did not meaningfully raise ACTH, cortisol, prolactin, FSH, LH or TSH. Supplied strictly for laboratory research use only, not for human or veterinary use.

How it works

Ipamorelin binds the GHS-R1a receptor on somatotroph cells of the anterior pituitary and, to a lesser degree, in the hypothalamus. GHS-R1a is a G-protein-coupled receptor whose activation drives the phospholipase-C pathway, raising intracellular inositol trisphosphate and calcium and triggering the release of stored growth hormone. This is a different pathway from that of GHRH analogues such as sermorelin or CJC-1295, which act through the GHRH receptor and cyclic AMP; the two mechanisms are complementary, which is why ghrelin mimetics and GHRH analogues are frequently paired in research protocols.

The trait that set ipamorelin apart from the earlier peptides GHRP-6 and GHRP-2 is receptor selectivity at the pituitary. In the Raun work it released GH at doses far below those needed to touch the hypothalamic-pituitary-adrenal axis: no significant change in ACTH or cortisol was seen even at doses exceeding 200-fold the ED₅₀ for GH release. It also releases GH in a pulsatile, feedback-preserving manner rather than clamping levels high, which is the property most examined in the research literature.

What the research shows

The foundational quantitative data come from Raun et al. (1998). In isolated rat pituitary cells ipamorelin released GH with an EC₅₀ of 1.3 nmol/l and a maximal effect of about 85% of the GHRP-6 reference, and in conscious swine it raised plasma GH with an ED₅₀ of 2.3 nmol/kg to a peak (E_max) of roughly 65 ng/ml, closely matching GHRP-6 (74 ng/ml) while avoiding any ACTH or cortisol rise. Later rodent work by Johansen et al. (1999) showed a dose-dependent increase in longitudinal bone growth without a measurable change in total IGF-1, and Svensson et al. (2000) found that chronic dosing increased tibial and vertebral bone mineral content in adult female rats.

Compared with related peptides

Against the reference GHRPs, ipamorelin sits between GHRP-6 and GHRP-2 on potency: GHRP-2 was more potent in vivo (ED₅₀ ~0.6 nmol/kg) but reached a lower peak GH (~56 ng/mL) and, like GHRP-6, drove up ACTH and cortisol. Ipamorelin's ED₅₀ of 2.3 nmol/kg and peak of ~65 ng/mL therefore give it the strongest efficacy-to-selectivity balance of the group in the Raun data. Because it works through GHS-R1a rather than the GHRH receptor, it is mechanistically distinct from GHRH analogues such as sermorelin and CJC-1295, and the two classes are often studied together.

Side Effects

Dedicated long-term human safety data for ipamorelin are limited: its clinical development stopped after mid-stage trials, so most of what we know comes from a single controlled postoperative-ileus study plus the broader growth-hormone-secretagogue class. A defining feature reported in the preclinical work is selectivity: ipamorelin stimulates growth-hormone release without meaningfully raising ACTH, cortisol, or prolactin, unlike some earlier peptides in its class. Many of the entries below are extrapolated from related ghrelin-receptor agonists and are labeled as such, because effect-specific ipamorelin data in humans are sparse.

In the one controlled human trial, ipamorelin at the tested dose was well tolerated, with adverse events largely attributable to recent surgery rather than the peptide itself. Its reported selectivity for growth-hormone release, sparing cortisol and prolactin, is a genuine pharmacological advantage over older secretagogues, but the class-based effects on fluid balance, appetite, and glucose remain the main theoretical concerns. Long-term, repeated-dosing safety in humans has not been established.

At a glance

Dosing

Ipamorelin has no approved human dosing regimen. It reached phase 2 clinical testing but was never marketed, so the figures below are the doses used in specific research studies, not a recommended protocol. The values come from the original preclinical pharmacology work and from the human trials that followed. They are provided as educational context for laboratory research use only.

There is no established human dosing regimen for ipamorelin: the phase 2 ileus trial did not meet its primary endpoint, and development did not continue to approval. The doses above reflect what was administered in the cited studies and are shared strictly as educational information for laboratory research use only.

Preparing it

The vial ships as a lyophilized powder and is reconstituted with bacteriostatic water (or sterile water for single-session work) before use. Choose a diluent volume that gives a concentration convenient to read on a U-100 syringe. See reconstitution for the method and the concentration formula for working out the diluent.

Where to go next

Last updated on July 3, 2026