Quick answer: Ipamorelin is a five-residue peptide of about 712 Da; GHRP-2 is a six-residue peptide of about 817 Da. Both act at the ghrelin receptor. A purity percentage cannot tell them apart, but a measured mass on the certificate can.
A pentapeptide and a hexapeptide from the same family
Ipamorelin and GHRP-2 both belong to the growth hormone secretagogue family, and both act at the ghrelin receptor. Buyers meet them in the same catalog sections and the same search results. They are different molecules: one is a five-residue peptide built around an unusual aminoisobutyric acid, the other a six-residue peptide with a different set of D-amino acids.
This guide compares them on origin, structure, receptor background, what the literature reports and what a certificate should show. It is background for laboratory research use only. Nothing here describes an effect or a use in people or animals. Single-compound background is in the ipamorelin research overview and the explainer what is ipamorelin.
Origin: two designs from the same receptor puzzle
GHRP-2 grew out of the same program that produced GHRP-6 in the 1980s. It is a hexapeptide that replaced several residues of the earlier template with others, among them D-alanine and D-2-naphthylalanine. Ipamorelin came from a separate effort at Novo Nordisk in the 1990s. Raun and colleagues described it in 1998 as a pentapeptide and reported that, in their animal and cell models, it released growth hormone with less effect on other pituitary hormones than earlier compounds in the family.
The word selective in that title is the reason the two peptides are compared so often. It is a claim from one group's preclinical work, and a methods section should cite the paper rather than repeat it as a general property. Broader context on how the family works is in sermorelin vs. ipamorelin, which covers the other main class of growth hormone research peptides.
Side-by-side comparison
| Feature | Ipamorelin | GHRP-2 |
|---|---|---|
| Family | Growth hormone secretagogue (pentapeptide) | Growth hormone-releasing peptide (hexapeptide) |
| Sequence | Aib-His-D-2-Nal-D-Phe-Lys-NH2 | D-Ala-D-2-Nal-Ala-Trp-D-Phe-Lys-NH2 |
| Length | 5 residues | 6 residues |
| Approximate mass | About 712 Da | About 817 Da |
| Main receptor | Ghrelin receptor (GHS-R1a) | Ghrelin receptor (GHS-R1a) |
| Foundational paper | Raun et al., 1998 | 1980s Bowers-program work |
| Key identity check | Measured mass near 712 Da | Measured mass near 817 Da |
| Listed by V8 | Yes, research use only | No |
Structure: different length, different building blocks
Ipamorelin has the sequence Aib-His-D-2-Nal-D-Phe-Lys-NH2. Aib is alpha-aminoisobutyric acid, a non-natural residue that resists enzymatic cleavage at the front of the chain. Its molecular weight is about 712 Da.
GHRP-2 has the sequence D-Ala-D-2-Nal-Ala-Trp-D-Phe-Lys-NH2, with an amidated C-terminus. It is one residue longer and weighs about 817 Da. Both contain D-2-naphthylalanine and D-phenylalanine, which is why the two can look alike in a quick glance at a sequence. The gap of roughly 105 Da is large enough that any mass measurement separates them at once.
Neither peptide has a metal, a lipid chain or an attached linker. Both are lyophilized powders, and both are small enough that a mass reading is a strong identity check.
Receptor background
Both compounds are agonists at the growth hormone secretagogue receptor type 1a. Howard and colleagues cloned that receptor in 1996, and Kojima and colleagues identified ghrelin as its natural ligand in 1999. A review by Smith and coworkers summarizes how the synthetic peptides and the receptor were linked together.
Because the target is shared, the differences between the two peptides appear mainly in structure, size and in which papers used which compound. A design that cites work on one cannot silently substitute the other.
What the published work reports
The Raun paper on ipamorelin is the foundational reference for that compound, and later work places it in the same receptor family as other secretagogues. GHRP-2 has a larger body of older pharmacology, including studies in animal models and in cell preparations. This guide does not summarize clinical papers, because those fall outside a research-use catalog.
For a reader choosing between them for a study, the useful question is which compound the cited papers used. Papers often use shorthand names, and a trade or nickname can hide whether the five-residue or the six-residue peptide was meant.
What a certificate should show
The identity line matters. A reading near 712 Da fits ipamorelin and a reading near 817 Da fits GHRP-2. HPLC purity alone cannot say which peptide is in the vial, since both can give one sharp peak. Look for a measured mass next to the expected mass, the exact compound name, and a lot identifier and test date that match the vial. For background on reading these documents, see understanding HPLC purity and how to read a COA.
For a peptide with several D-residues, read the chromatogram as well as the percentage, because stereochemical impurities can sit near the main peak. For cell work, look for an endotoxin result and a sterility statement.
V8 Peptides publishes certificates for only some products. Where one exists, it reports HPLC purity and identity, endotoxin and PCR sterility. This article describes general buyer practice and is not a statement about any particular lot. V8 lists ipamorelin at ipamorelin for research use only; GHRP-2 is not part of the V8 catalog. More pages: ipamorelin purity testing, where to buy ipamorelin and the blend explainer CJC-1295 + ipamorelin explained.
Handling and record keeping
Keep the powder cold, dry and away from light, and write the opening date on the vial. Plan aliquots before opening a vial. This guide gives no volumes or concentrations, because those belong in a laboratory's own validated procedure.
In the notebook, record the exact name and residue count, lot, supplier, certificate date and storage conditions. Where two secretagogues share a study, run them as separate reagents with separate controls.
Frequently asked questions
Are ipamorelin and GHRP-2 the same kind of peptide?
They belong to the same receptor family but are different molecules. Ipamorelin has five residues and GHRP-2 has six.
How different are they in size?
About 712 Da for ipamorelin against about 817 Da for GHRP-2, a gap of roughly 105 Da.
Which receptor do they act on?
Both act at the growth hormone secretagogue receptor type 1a, the receptor that also binds ghrelin.
What is Aib?
Alpha-aminoisobutyric acid, a non-natural amino acid at the front of ipamorelin that resists enzymatic cleavage.
Why is ipamorelin called selective?
The 1998 Raun paper reported less effect on other pituitary hormones in its models. It is a preclinical claim from that work and should be cited, not repeated as a general rule.
Can HPLC purity tell me which peptide I have?
Not on its own. Both can show one clean peak. A measured mass next to the expected mass is the identity check.
Does V8 sell GHRP-2?
No. V8 lists ipamorelin, for laboratory research use only.
Why read the chromatogram and not just the percentage?
With several D-residues, stereochemical impurities can sit close to the main peak and be hidden inside a single headline number.
Does this article describe a use in people?
No. It summarizes structure, published background and analytical practice. No product is sold for human or animal consumption.
What should I record for each vial?
The exact compound name, lot identifier, certificate date, supplier, storage conditions and the date the vial was opened.
References
- Raun K, Hansen BS, Johansen NL, et al. Ipamorelin, the first selective growth hormone secretagogue. Eur J Endocrinol. 1998;139(5):552-561.
- Howard AD, Feighner SD, Cully DF, et al. A receptor in pituitary and hypothalamus that functions in growth hormone release. Science. 1996;273(5277):974-977.
- Kojima M, Hosoda H, Date Y, Nakazato M, Matsuo H, Kangawa K. Ghrelin is a growth-hormone-releasing acylated peptide from stomach. Nature. 1999;402(6762):656-660.
- Smith RG, Van der Ploeg LH, Howard AD, et al. Peptidomimetic regulation of growth hormone secretion. Endocr Rev. 1997;18(5):621-645.