GHRP-2 vs GHRP-6
GHRP-2 and GHRP-6 are synthetic hexapeptide growth hormone releasing peptides that act at the ghrelin receptor. This page compares their sequences, receptor pharmacology, human physiology studies, regulatory and WADA status, and the oxidation risks shared by their tryptophan-containing structures.
GHRP-6 was one of the first synthetic growth hormone releasing peptides, designed in the early 1980s from modified enkephalin-like structures before the receptor it acts on was known. GHRP-2, also known as pralmorelin, was developed later in the same series with changes to the N-terminal residues. Both were later shown to activate the growth hormone secretagogue receptor (GHS-R1a), which was subsequently identified as the receptor for the hormone ghrelin.
The two are close structural relatives, differing in two of their six positions, and they are often discussed together as early reference compounds in ghrelin receptor pharmacology. Neither is approved by the FDA, and both have been studied mainly in animal pharmacology and short human physiology studies rather than in treatment trials.
Side-by-side
| Attribute | GHRP-2 | GHRP-6 |
|---|---|---|
| Sequence | D-Ala-D-2-Nal-Ala-Trp-D-Phe-Lys-NH<sub>2</sub> | His-D-Trp-Ala-Trp-D-Phe-Lys-NH<sub>2</sub> |
| Length | 6 residues | 6 residues |
| Key structural features | D-alanine and D-2-naphthylalanine at positions 1–2; one tryptophan; amidated C-terminus | Histidine and D-tryptophan at positions 1–2; two tryptophans; amidated C-terminus |
| Receptor target | GHS-R1a (ghrelin receptor) | GHS-R1a (ghrelin receptor); CD36 binding also reported |
| Research areas | Growth hormone secretion physiology, pituitary function testing, appetite | Growth hormone secretion physiology, appetite, cardiac injury in animal models |
| Evidence level | Early-clinical (human physiology and diagnostic studies) | Early-clinical (human physiology studies) |
| FDA / compounding | Not FDA-approved; check current compounding guidance | Not FDA-approved; check current compounding guidance |
| WADA | Prohibited under S2 (GH secretagogues) | Prohibited under S2 (GH secretagogues) |
| Analytical pitfalls | Unnatural D-2-Nal residue; tryptophan oxidation; counter-ion content | Two tryptophans make oxidation more likely; counter-ion content |
| Storage | Lyophilized at -20 °C, protected from light and moisture | Lyophilized at -20 °C, protected from light and moisture |
Structural differences
The two peptides share their last four residues, Ala-Trp-D-Phe-Lys-NH2. GHRP-6 begins with histidine and D-tryptophan, while GHRP-2 replaces these with D-alanine and 3-(2-naphthyl)-D-alanine (D-2-Nal), a bulky unnatural aromatic residue. As a result GHRP-2 contains one tryptophan and GHRP-6 contains two. These changes alter potency and receptor interactions while keeping the core motif needed for ghrelin receptor activation. Use the sequence analyzer to compare expected masses; unnatural residues such as D-2-Nal must be entered correctly.
Pharmacology in published studies
In animal and human physiology studies, both peptides stimulated growth hormone release and showed synergy with GHRH. GHRP-2 was generally reported as the more potent of the two at the pituitary. Both were also associated with rises in prolactin and cortisol, and GHRP-6 in particular has been linked to increased food intake, consistent with ghrelin receptor activity in appetite circuits. Later compounds such as ipamorelin were designed partly to reduce these off-target hormonal effects. Human findings come from short mechanistic studies, not trials of clinical outcomes.
Quality and handling
Both peptides are short enough that synthesis impurities such as deletion sequences are relatively easy to resolve by HPLC, but their aromatic residues create other concerns. Tryptophan oxidizes under light and air exposure, producing species with mass increases that mass spectrometry can detect, and GHRP-6 has two susceptible residues. D-amino acid content matters for activity, yet standard reversed-phase HPLC and mass spectrometry do not distinguish D from L forms; chiral analysis is needed to detect racemization. Counter-ion content can be a large share of the mass of such small peptides.
Frequently asked questions
What is the difference between GHRP-2 and GHRP-6?
Both are synthetic hexapeptides that activate the ghrelin receptor and share their last four residues. GHRP-2 starts with D-alanine and D-2-naphthylalanine, while GHRP-6 starts with histidine and D-tryptophan. In published studies GHRP-2 was generally reported to be more potent for growth hormone release, while GHRP-6 has been more strongly associated with increased appetite.
Are GHRP-2 and GHRP-6 FDA approved?
No. Neither GHRP-2 nor GHRP-6 is approved by the FDA for any use, and neither is an approved drug product in the US. Their status for pharmacy compounding should be checked against current FDA guidance. Both are prohibited at all times in sport under section S2 of the WADA Prohibited List as growth hormone secretagogues.
Is GHRP-2 the same as pralmorelin?
Yes. Pralmorelin is the nonproprietary name associated with GHRP-2, the hexapeptide D-Ala-D-2-Nal-Ala-Trp-D-Phe-Lys-NH2. Research material may be labeled under either name. Regardless of the name used, a certificate of analysis should confirm the expected mass for this exact sequence and state the salt form, since GHRP-2 and GHRP-6 are easy to confuse.
Full entries
- GHRP-2
GHRP-2 (pralmorelin) is a synthetic hexapeptide that stimulates growth hormone release by activating the ghrelin receptor. It has been studied in human endocrine testing and is not approved by the FDA.
- GHRP-6
GHRP-6 is a synthetic hexapeptide that stimulates growth hormone release by activating the ghrelin receptor (GHS-R1a). It was one of the first growth hormone secretagogues and is not approved for any use.
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