Ipamorelin, GHRP-6 and GHRP-2 compared
Three growth hormone secretagogue receptor ligands: sequences, what the literature reports as differing, and the practical bench differences.
Ipamorelin, GHRP-6 and GHRP-2 are the three most-studied growth hormone secretagogue receptor ligands in the research peptide market, and they are frequently described as variations on one theme. Chemically and pharmacologically they are distinct compounds with different sequences, different selectivity profiles and different research literatures. This note compares them for researchers reading that literature or designing receptor work. Only Ipamorelin is in the Alphex catalogue; the others are described here for context. All Alphex products are for laboratory and in-vitro research only.
The three compounds
- GHRP-6 (His-D-Trp-Ala-Trp-D-Phe-Lys-NH2, 873.0 g/mol): the first of the growth hormone releasing peptides to be widely studied, developed from enkephalin-derived leads in the 1980s. Six residues, two D-amino acids, C-terminally amidated.
- GHRP-2 (D-Ala-D-2-Nal-Ala-Trp-D-Phe-Lys-NH2, 817.0 g/mol, also called pralmorelin): a later-generation secretagogue with higher potency in the assays of the time.
- Ipamorelin (Aib-His-D-2-Nal-D-Phe-Lys-NH2, 711.9 g/mol, NNC 26-0161): designed in the 1990s for receptor selectivity, notable for the non-proteinogenic Aib residue at the N-terminus and the absence of tryptophan. See the Ipamorelin guide.
All three are synthetic ligands at the growth hormone secretagogue receptor GHS-R1a, the receptor for the endogenous peptide ghrelin, and all three contain D-amino acids and C-terminal amidation to resist enzymatic breakdown.
What the literature reports as differing
- Selectivity. The design goal for Ipamorelin was a secretagogue that did not appreciably affect other pituitary hormone axes in the assay systems used; published characterisation reported comparatively little effect on cortisol and prolactin release relative to GHRP-6 and GHRP-2 in those systems. This selectivity claim belongs to specific preclinical assays and should be read in that context, not generalised.
- Potency. GHRP-2 was reported as more potent than GHRP-6 in the assays of its era; Ipamorelin's potency sits in a similar range with the selectivity difference above.
- Structure-activity work. The role of the aromatic D-residues (D-2-naphthylalanine, D-phenylalanine, D-tryptophan) in receptor binding, and of Aib in conferring resistance to degradation, is the subject of a coherent medicinal-chemistry literature across the family.
Nothing in this literature establishes any use outside the laboratory, and Alphex supplies Ipamorelin as a laboratory reagent only.
Practical differences for the bench
- UV behaviour: GHRP-6 and GHRP-2 contain tryptophan and absorb usefully at 280 nm; Ipamorelin does not contain Trp but its naphthylalanine gives absorbance near 280 nm as well. All are analysed for purity at 220 nm. See 220 nm versus 280 nm.
- Oxidation: tryptophan-containing peptides (GHRP-6, GHRP-2) are more prone to photo-oxidation than Ipamorelin. See light-sensitive peptides.
- Solubility: all three are moderately hydrophobic for their size because of the aromatic D-residues; give high-concentration stocks time to dissolve. See the solubility guide.
- Molar comparison: 712, 817 and 873 g/mol; compare on a molar basis with net-content correction. See calculating concentration.
- Stereochemistry: all three contain D-residues, so mass alone cannot confirm the correct isomer; HPLC against a reference standard does. See reference standards.
Verification
Alphex supplies Ipamorelin at 99+% HPLC purity (220 nm, reference standard), batch-numbered, from UK stock, with the certificate available before purchase. We do not stock GHRP-2 or GHRP-6; see why the catalogue is small. If you buy them elsewhere, the questions to ask apply.
Alphex research peptides are supplied for laboratory and in-vitro research by qualified researchers only. They are not authorised for human or veterinary use.
Research use only. Alphex products are supplied exclusively for laboratory and in-vitro research by qualified researchers. They are not authorised for human or veterinary use, and nothing in this note is advice on any such use.
Published 30 June 2026. Alphex reviews research notes when the testing method, the catalogue or UK guidance changes.