Quick answer: Ipamorelin is a five-residue peptide of about 712 Da; GHRP-6 is a six-residue peptide of about 873 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 its much older hexapeptide relative
Ipamorelin and GHRP-6 both belong to the growth hormone secretagogue family and both act at the ghrelin receptor. GHRP-6 is the older design, described in the 1980s. Ipamorelin came a decade later from a separate effort, and its authors framed it as more selective. Buyers meet them in the same search results, but they are different molecules with different lengths, sequences and masses.
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 what is ipamorelin explainer.
Origin: two decades of design work
Bowers and colleagues described GHRP-6 in 1984 as a synthetic hexapeptide that released growth hormone from pituitary cells and in animal models. It used D-amino acids, an early sign that the family was designed to resist breakdown. The receptor it acted on was unknown at the time.
Ipamorelin was reported by Raun and colleagues in 1998 under the title describing it as the first selective growth hormone secretagogue. The word selective refers to that group's preclinical comparisons with other pituitary hormones. It is a claim from one paper and should be cited as such rather than repeated as a general property. The receptor had been cloned in 1996 by then, and ghrelin was identified in 1999, which placed both peptides in a defined pharmacology.
For how ipamorelin sits next to other secretagogues, see the hexarelin vs. ipamorelin comparison and sermorelin vs. ipamorelin.
Side-by-side comparison
| Feature | Ipamorelin | GHRP-6 |
|---|---|---|
| Family | Growth hormone secretagogue (pentapeptide) | Growth hormone-releasing peptide (hexapeptide) |
| Sequence | Aib-His-D-2-Nal-D-Phe-Lys-NH2 | His-D-Trp-Ala-Trp-D-Phe-Lys-NH2 |
| Length | 5 residues | 6 residues |
| Approximate mass | About 712 Da | About 873 Da |
| Main receptor | Ghrelin receptor (GHS-R1a) | Ghrelin receptor (GHS-R1a) |
| Foundational paper | Raun et al., 1998 | Bowers et al., 1984 |
| Key identity check | Measured mass near 712 Da | Measured mass near 873 Da |
| Listed by V8 | Yes, research use only | No |
Structure: five residues against six
Ipamorelin is Aib-His-D-2-Nal-D-Phe-Lys-NH2. The first residue, aminoisobutyric acid, is a non-natural amino acid with a doubled methyl group that blocks enzymatic cleavage at the N-terminus. GHRP-6 is His-D-Trp-Ala-Trp-D-Phe-Lys-NH2, a six-residue chain with two tryptophans.
The two share a histidine, a D-aromatic residue, D-Phe and a C-terminal lysine amide, which is why they are often described as relatives. They differ in length and in the aromatic residues used. Ipamorelin is about 712 Da and GHRP-6 is about 873 Da, a gap of roughly 161 Da.
That gap is easy for a mass spectrometer to resolve. HPLC purity alone does not name the molecule, since both can give one clean peak. The identity line on a certificate is what separates them.
Receptor background
Both peptides are agonists at the growth hormone secretagogue receptor type 1a, the receptor that also binds ghrelin. In receptor terms they are in the same class, and any difference reported between them in the literature is a difference in the models and assays used as much as in the molecules.
GHRP-6 literature includes a wider range of cell and tissue reports collected over several decades, while ipamorelin literature is smaller and centered on its original selectivity work. A methods section should name the exact peptide and cite the paper behind each claim, because the evidence bases are not interchangeable.
What the published work reports
Most of the published work on both is receptor pharmacology in cell lines and animal models. Review articles such as Smith and colleagues (1997) give the best map of the family. Be careful with summary tables that line up numbers taken from separate papers, since assay, species, preparation and purity can account for more of any apparent difference than the molecules do.
This guide does not rank the peptides or describe an outcome for either. Its purpose is to help a reader tell the molecules apart on paper and in the vial.
What a certificate should show
Look for a measured mass next to the expected value, 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.
Read the chromatogram, not just the percentage. Ipamorelin contains several non-natural or D-configured residues, and synthesis can leave deletion or racemized sequences 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 and does not list GHRP-6. More buyer-side guidance is in where to buy ipamorelin, ipamorelin purity testing and choosing a peptide supplier.
Handling and record keeping
Keep lyophilized peptide cold, dry and away from light until use, 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-6 the same kind of peptide?
They belong to the same receptor family but are different molecules. Ipamorelin has five residues and GHRP-6 has six.
How different are they in size?
About 712 Da for ipamorelin against about 873 Da for GHRP-6, a gap of roughly 161 Da.
Which receptor do they act on?
Both act at the growth hormone secretagogue receptor type 1a, the receptor that also binds ghrelin.
Which came first?
GHRP-6 was described in 1984. Ipamorelin was reported in 1998.
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-6?
No. V8 lists ipamorelin, for laboratory research use only.
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
- Bowers CY, Momany FA, Reynolds GA, Hong A. On the in vitro and in vivo activity of a new synthetic hexapeptide that acts on the pituitary to specifically release growth hormone. Endocrinology. 1984;114(5):1537-1545.
- 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.