What does selective mean for ipamorelin?

That it released GH without the cortisol and prolactin increases seen with earlier secretagogues, the specific claim in Raun's 1998 paper title.

α-aminoisobutyric acid, a non-proteinogenic residue whose quaternary alpha carbon blocks peptidase access. It is the same residue semaglutide uses to block DPP-4.

What Is Ipamorelin? The First Selective Ghrelin Agonist

The short answer

Ipamorelin is a synthetic pentapeptide, Aib-His-D-2-Nal-D-Phe-Lys-NH2, at 711.9 Da. It acts at the ghrelin receptor and was described by Raun and colleagues in 1998 as the first selective growth hormone secretagogue. Selective here means it released GH without the cortisol and prolactin effects of earlier compounds.

Key facts

Sequence: Aib-His-D-2-Nal-D-Phe-Lys-NH2
Residues: 5, C-terminal amide
Molecular weight: 711.9 Da
Formula: C38H49N9O5
CAS number: 170851-70-4
PubChem CID: 9831659
Development code: NNC 26-0161 (Novo Nordisk)
Target: Ghrelin receptor (GHS-R1a)

What selective meant

Raun and colleagues titled their 1998 paper in the European Journal of Endocrinology 'Ipamorelin, the first selective growth hormone secretagogue'. The selectivity claim is specific: earlier secretagogues released GH but also raised cortisol and prolactin, which confounds both research and any therapeutic use. Ipamorelin was reported to release GH without those accompanying effects.

The unusual residues

Only one of its five residues is an ordinary L-amino acid. Position 1 is α-aminoisobutyric acid (Aib), a non-proteinogenic residue with a quaternary alpha carbon. Positions 3 and 4 are D-amino acids: D-2-naphthylalanine and D-phenylalanine. Position 2 is histidine and position 5 lysine, with a C-terminal amide. This is a heavily engineered molecule rather than a natural sequence.

Research material referenced

CJC-1295 + Ipamorelin 5+5mg, third-party HPLC tested

Buy CJC-1295 + Ipamorelin · £36.99

Why Aib appears here and in semaglutide

This is a real cross-connection. Aib's quaternary alpha carbon makes adjacent bonds poor substrates for peptidases, which is why semaglutide carries Aib at position 8 to block DPP-4. Two entirely unrelated peptides, thirty years apart, reach for the same residue to solve the same problem: protease resistance in a short peptide.

What D-amino acids do

Proteases evolved to cleave L-amino acid backbones and generally cannot process D-residues. Two D-residues in a five-residue peptide makes most of it enzymatically inaccessible. Combined with Aib and the C-terminal amide, which blocks carboxypeptidases, nearly every position is protected. The peptide is short because it does not need length to survive.

The ghrelin receptor

Ipamorelin acts at the growth hormone secretagogue receptor GHS-R1a, whose endogenous ligand is ghrelin. That is a different pathway from CJC-1295's, which acts at the GHRH receptor. Both converge on pituitary GH release, which is the basis for studying them together.

Regulatory position

Ipamorelin holds no marketing authorisation from the MHRA, EMA or FDA. Growth hormone secretagogues are prohibited in sport under the WADA list. It is supplied here for laboratory research only.

Frequently asked questions

What does selective mean for ipamorelin?: That it released GH without the cortisol and prolactin increases seen with earlier secretagogues, the specific claim in Raun's 1998 paper title.
What is Aib?: α-aminoisobutyric acid, a non-proteinogenic residue whose quaternary alpha carbon blocks peptidase access. It is the same residue semaglutide uses to block DPP-4.

Extended research context

The CJC-1295 & Ipamorelin deep dive

Deep dive: why CJC-1295 and Ipamorelin are studied together

CJC-1295 is a modified GHRH (growth-hormone-releasing hormone) analogue; Ipamorelin is a selective growth-hormone secretagogue that binds the ghrelin receptor (GHS-R1a). In pituitary-cell research models the two act on independent pathways whose downstream effect converges on GH release. CJC-1295 amplifies the endogenous GHRH signal while Ipamorelin adds a separate ghrelin-pathway stimulus. That's why supplier catalogues frequently package them together as a research reference blend.

DAC vs no-DAC: which CJC-1295 is which

'CJC-1295 with DAC' contains a Drug Affinity Complex (a Lys-maleimide moiety) that binds serum albumin and extends half-life to several days. 'CJC-1295 no-DAC' (also called Modified GRF 1-29) lacks the linker and clears in minutes. These are pharmacologically different peptides. A CoA must specify which form is in the vial; mass differs (~3,367 Da with DAC vs ~3,367 minus linker for no-DAC).

Ipamorelin's selectivity profile

Unlike earlier GHS-R agonists (e.g. GHRP-6), Ipamorelin was engineered for minimal cross-activity at cortisol- and prolactin-releasing pathways in research models. That receptor selectivity is why it is the reference secretagogue for controlled pituitary-cell studies.

Research applications

▸Pituitary-cell GH-release assays (comparator vs GHRH and hexarelin)
▸Half-life comparison studies: DAC vs no-DAC CJC-1295 forms
▸Ghrelin-receptor binding assays for Ipamorelin analogue development
▸Analytical HPLC method development for lipidated GHRH analogues
▸Stability testing under refrigerated storage

Handling checklist

✓Store lyophilised at −20 °C long-term
✓Reconstitute in bacteriostatic water; both peptides dissolve readily
✓Aliquot immediately, refrigerate at 2–8 °C, use within 28 days
✓Confirm salt form and DAC/no-DAC status on CoA before starting a study
✓Do not use for human administration (research reference only)

Common research-handling mistakes

Learnt from thousands of researcher orders across our UK labs.

✗ Confusing DAC and no-DAC CJC-1295

Fix: Check the CoA. The two have very different pharmacokinetics.

✗ Assuming Ipamorelin acts on GHRH receptors

Fix: It binds the ghrelin receptor (GHS-R1a), a separate pathway from CJC-1295.

✗ Storing reconstituted solution at room temperature

Fix: Refrigerate 2–8 °C after reconstitution.

Continue researching

Peer-reviewed guides, comparators and matched reference materials.

Primary sources & clinical trials

Peer-reviewed research and registered trials from PubMed, ClinicalTrials.gov, PubChem, FDA and NIH. All links open in a new tab and point to the primary source, so every claim can be verified at origin.

UKP

Written and reviewed by

The UK Peptides Editorial Team · Research library, UK Peptides

The editorial team is responsible for supplier selection, batch release decisions and the content published in this research library. Every article here is sourced to primary literature and every product page to a signed third-party certificate. Corrections are made in place and the review date updated.

How we write and check this content Report a factual error in this article

More CJC-1295 & Ipamorelin articles

Popular across the research hub

One flagship guide from every other research category.

← Back to Forum

What Is Ipamorelin? Sequence, Receptor and Selectivity