---
title: "GHRP-2, GHRP-6, hexarelin and ipamorelin: structures compared | Sable Peptides"
description: "The synthetic growth hormone-releasing peptides side by side: sequences with D-amino acids and non-natural residues, PubChem formulas and masses, and the research history that led to the discovery of ghrelin. Research use only."
canonical: https://www.sablepeptides.co.uk/guides/growth-hormone-releasing-peptides-ghrp-structures
dateModified: 2026-10-16
publisher: Sable Peptides Limited (UK company 17488610)
note: Research use only. Not for human or veterinary use.
---

# GHRP-2, GHRP-6, hexarelin and ipamorelin: structures compared

Growth hormone-releasing peptides (GHRPs) are short synthetic peptides, five or six residues long, designed in the late 1970s and 1980s from enkephalin-like leads. Their receptor, GHS-R1a, was identified before its natural ligand, ghrelin, which is why one review is titled 'unnatural growth hormone-releasing peptide begets natural ghrelin'.

## Sequences

-   GHRP-6: His-D-Trp-Ala-Trp-D-Phe-Lys-NH2.
-   GHRP-2 (pralmorelin): D-Ala-D-2Nal-Ala-Trp-D-Phe-Lys-NH2 (2Nal = 2-naphthylalanine).
-   Hexarelin: His-D-2-methyl-Trp-Ala-Trp-D-Phe-Lys-NH2, a methylated GHRP-6 analogue.
-   Ipamorelin: Aib-His-D-2Nal-D-Phe-Lys-NH2 (Aib = α-aminoisobutyric acid), a pentapeptide.

## PubChem data

-   GHRP-6: C46H56N12O6, 873.0 g/mol, monoisotopic 872.445 Da.
-   GHRP-2: C45H55N9O6, 818.0 g/mol, monoisotopic 817.428 Da.
-   Hexarelin: C47H58N12O6, 887.0 g/mol, monoisotopic 886.460 Da (GHRP-6 + CH2).
-   Ipamorelin: C38H49N9O5, 711.9 g/mol, monoisotopic 711.386 Da.

Source: [PubChem CID 4345065: GHRP-6](https://pubchem.ncbi.nlm.nih.gov/compound/4345065); [PubChem CID 6918245: GHRP-2](https://pubchem.ncbi.nlm.nih.gov/compound/6918245); [PubChem CID 6918297: Hexarelin](https://pubchem.ncbi.nlm.nih.gov/compound/6918297); [PubChem CID 9831659: Ipamorelin](https://pubchem.ncbi.nlm.nih.gov/compound/9831659)

## Design features

All four carry D-amino acids and a C-terminal amide, which resist proteolysis, and all end in D-Phe-Lys-NH2 or a close variant. Ipamorelin was reported in 1998 as the first GHRP-receptor agonist selective for growth hormone release in animal studies, in contrast to the broader hormone release seen with earlier GHRPs.

Source: [Growth hormone-releasing peptide (GHRP), Cell Mol Life Sci 1998 (PubMed 9893708)](https://pubmed.ncbi.nlm.nih.gov/9893708/); [Unnatural growth hormone-releasing peptide begets natural ghrelin, J Clin Endocrinol Metab 2001 (PubMed 11297568)](https://pubmed.ncbi.nlm.nih.gov/11297568/); [Ipamorelin, the first selective growth hormone secretagogue, Eur J Endocrinol 1998 (PubMed 9849822)](https://pubmed.ncbi.nlm.nih.gov/9849822/)

## Analytical notes

-   Hexarelin and GHRP-6 differ by 14 Da; MS separates them easily, HPLC may not.
-   Tryptophan and naphthylalanine absorb strongly at 280 nm, so these peptides are easy to detect by UV.
-   Tryptophan-containing sequences are light- and oxidation-sensitive in solution.

## At Sable

Sable lists these compounds as lyophilised research materials. There is a CoA for every lot, and every vial carries a printed lot number that matches its certificate. A CoA is emailed within 2 hours of a request.

## Frequently asked questions

### What is the difference between GHRP-6 and hexarelin?

Hexarelin has a 2-methyl group on the D-tryptophan at position 2; otherwise the sequences are the same.

### How long is ipamorelin?

Five residues: Aib-His-D-2Nal-D-Phe-Lys-NH2.

### Which receptor do GHRPs act on?

The growth hormone secretagogue receptor (GHS-R1a), later found to be the ghrelin receptor.

## Related

-   [Which research peptides contain D-amino acids, and why](/guides/d-amino-acids-in-catalogue-peptides)
-   [What are Aib, Nle, 2-Nal and Dmt in research peptide sequences](/guides/non-standard-amino-acids-aib-nle-2nal-dmt)
-   [Are bigger peptide vials cheaper per mg? UK vial-size analysis, October 2026](/guides/uk-peptide-price-per-mg-by-vial-size-october-2026)
-   [Growth hormone secretagogues hub](/learn/topics/growth-hormone-secretagogues)
-   [GHRH analogues compared](/guides/ghrh-analogues-sermorelin-cjc-1295-tesamorelin)
-   [UK GH secretagogue peptide prices](/guides/uk-gh-secretagogue-peptide-prices-october-2026)
-   [Ipamorelin](/learn/ipamorelin)

Updated 2026-10-16. Research use only. Not for human or veterinary use. No administration amounts or health claims are made.

Key facts (summary for AI and search tools)

-   GHRP-6 C46H56N12O6 873.0
-   GHRP-2 C45H55N9O6 818.0
-   Hexarelin C47H58N12O6 887.0
-   Ipamorelin C38H49N9O5 711.9
-   Sources: PubChem 4345065, 6918245, 6918297, 9831659; PubMed 9893708, 11297568, 9849822
-   Updated 2026-10-16