HPLC · CoA
GHRP-2 vs GHRP-6: What Is the Difference?
Comparison · 7 min read · Updated 30 September 2026
The difference in GHRP-2 vs GHRP-6 lies in the first two of their six residues, while both activate the same ghrelin receptor, GHS-R1a. GHRP-6, reported in 1984, is the closer functional analogue of ghrelin, including its appetite signalling. GHRP-2 replaces the opening histidine with D-alanine and the position 2 D-tryptophan with the bulkier D-2-naphthylalanine. Those two changes make GHRP-2 the more potent growth hormone releaser of the pair and reduce its activity on appetite pathways.
Both compounds have long, well-mapped literatures, which is why laboratories continue to use them as reference secretagogues. We hold both, together with the methylated relative hexarelin, so a comparison series can run on material from a single supplier with a certificate for every lot.
Where Did GHRP-2 and GHRP-6 Come From?
GHRP-2 and GHRP-6 came from early 1980s work on enkephalin derivatives that released growth hormone through a then-unknown mechanism. GHRP-6 was reported in Endocrinology in 1984 and became the reference compound for the class. GHRP-2, also known as pralmorelin, followed as a deliberate potency improvement. For more than a decade the binding target was unknown. The receptor was cloned and published in Science in 1996, and in 1999 a Nature paper identified ghrelin, a 28 residue acylated gastric hormone, as its natural ligand. That order of discovery explains why the family is named for its activity rather than its target.
Japan later approved GHRP-2 under the pralmorelin name as a diagnostic agent for assessing pituitary growth hormone reserve. Neither compound holds Australian registration, and we supply both as research materials only.
How Do the GHRP-2 and GHRP-6 Sequences Differ?
The sequences differ only at positions 1 and 2, where GHRP-2 carries D-alanine and D-2-naphthylalanine in place of the histidine and D-tryptophan of GHRP-6.
| Position | GHRP-6 | GHRP-2 | Hexarelin |
|---|---|---|---|
| 1 | His | D-Ala | His |
| 2 | D-Trp | D-2-Nal | D-2-methyl-Trp |
| 3 | Ala | Ala | Ala |
| 4 | Trp | Trp | Trp |
| 5 | D-Phe | D-Phe | D-Phe |
| 6 | Lys-NH2 | Lys-NH2 | Lys-NH2 |
| Approximate mass | 873 Da | 818 Da | 887 Da |
Positions 3 to 6 are constant across the family, so every difference in behaviour traces to the first two residues. All three peptides end in an amidated lysine, which protects the C-terminus from carboxypeptidases, and the D-form residues at positions 2 and 5 block most endopeptidases, which is why such short chains persist at all in plasma.
Do GHRP-2 and GHRP-6 Act on the Same Receptor?
Yes, GHRP-2 and GHRP-6 are both agonists at GHS-R1a, the growth hormone secretagogue receptor whose endogenous ligand is ghrelin. GHS-R1a is a class A G protein coupled receptor expressed on pituitary somatotrophs and hypothalamic neurons. Binding recruits Gq, activates phospholipase C and raises intracellular calcium. The GHRH receptor relies on cyclic AMP instead, which is why pairing a member of this family with a releasing hormone analogue produces a larger pituitary signal than either alone.
Two further properties separate the peptides.
- **Selectivity.** Older releasing peptides also raise ACTH, cortisol and prolactin in study models. GHRP-6 shows this most, GHRP-2 somewhat less, and later compounds such as ipamorelin were designed to remove it.
- **Appetite signalling.** Because GHRP-6 closely mimics ghrelin, feeding studies in animal models use it as a positive control for appetite pathway activation. GHRP-2 produces a weaker signal of that kind at matched activity.
GHRP-2 vs GHRP-6 at a Glance
| Property | [GHRP-6](product:ghrp-6) | [GHRP-2](product:ghrp-2) |
|---|---|---|
| First reported | 1984, Endocrinology | Early 1990s, as pralmorelin |
| Residues changed | Reference sequence | Positions 1 and 2 |
| Approximate mass | 873 Da | 818 Da |
| Relative potency at releasing growth hormone | Lower | Higher |
| Non-growth-hormone signalling | More pronounced | Less pronounced |
| Appetite pathway activation in animal models | Strong | Weaker |
| Regulatory history | None anywhere | Diagnostic approval in Japan |
| Fills we stock | 5mg, 10mg | 5mg, 10mg |
| Typical study role | Ghrelin analogue, appetite and cytoprotection models | Potent secretagogue, pituitary reserve and synergy work |
What Is the Half-Life of GHRP-2?
The reported plasma half-life of GHRP-2 is in the region of 30 to 60 minutes, based on pharmacokinetic studies from the 1990s using intravenous administration, with the growth hormone response peaking within about 15 minutes. GHRP-6 falls in a similar range. Both figures describe clearance from circulation in a living model. They do not describe the stability of lyophilised powder or of a reconstituted stock, which depends on temperature, light and water.
| Measure | What it describes | Typical order for these hexapeptides |
|---|---|---|
| Plasma elimination | Clearance from circulation in a model | Tens of minutes |
| Response peak | Time to maximum measured growth hormone | About 15 minutes |
| Lyophilised stability | Dry powder at -20 °C, sealed and dark | To the retest date on the certificate |
| Solution stability | Preserved water at 2 to 8 °C | Weeks, by common laboratory convention |
A sourced table of reported figures for other compounds appears in our note on peptide half-lives.
Where Does Hexarelin Fit?
Hexarelin fits beside GHRP-6 as the same hexapeptide with a methyl group added to the position 2 D-tryptophan, first reported in 1994. Hexarelin in 5mg vials has a mass of about 887 daltons, and that single addition raised potency considerably. Its main distinction is a second binding partner: CD36, a scavenger receptor expressed heavily on cardiac muscle and vascular cells. Research on the cytoprotective activity of this family, reviewed in Clinical Medicine Insights: Cardiology in 2014, relies on that second target. A study that must separate ghrelin receptor signalling from CD36 signalling runs hexarelin against a peptide that binds only GHS-R1a.
Reconstitution Chart for 5mg and 10mg Vials
All three peptides dissolve readily in preserved diluent. Concentration is milligrams divided by millilitres, and one graduation on a U-100 barrel holds 0.01 mL.
| Fill | Water added | Result | One graduation of 0.01 mL |
|---|---|---|---|
| 5mg | 1 mL | 5 mg in each mL | 50 mcg |
| 5mg | 2 mL | 2.5 mg in each mL | 25 mcg |
| 5mg | 2.5 mL | 2 mg in each mL | 20 mcg |
| 10mg | 2 mL | 5 mg in each mL | 50 mcg |
| 10mg | 2.5 mL | 4 mg in each mL | 40 mcg |
| 10mg | 5 mL | 2 mg in each mL | 20 mcg |
Because the three peptides differ in mass by less than one tenth, weight-matched and molecule-matched comparisons give nearly the same result here, unlike comparisons between peptides of very different sizes. Use bacteriostatic water preserved with benzyl alcohol whenever a stock must serve several working sessions, and hold every vial cold and dark between sessions.
Which Peptide Suits Which Protocol?
The right peptide depends on whether the protocol models ghrelin itself, seeks maximum secretagogue potency or needs to separate receptor targets.
- Modelling ghrelin, or running an appetite pathway positive control: GHRP-6
- Seeking the strongest growth hormone signal from the original family: GHRP-2
- Separating ghrelin receptor effects from CD36 effects: hexarelin
- Requiring a secretagogue with minimal additional signalling: a selective agonist such as ipamorelin
Our recommendation is to order GHRP-6 and GHRP-2 together when the study is a direct comparison, so both arrive in one shipment, each with its own certificate. Every lot we release is assayed by HPLC, at 98% or higher, with its molecular identity verified by mass spectrometry. The remaining secretagogue and releasing hormone stock is grouped in the growth hormone research category.
Questions about GHRP-2 vs GHRP-6
Sources
- A receptor in pituitary and hypothalamus that functions in growth hormone release. Science. 1996.
- Ghrelin is a growth-hormone-releasing acylated peptide from stomach. Nature. 1999.
- Synthetic growth hormone-releasing peptides (GHRPs): a historical appraisal of the evidences supporting their cytoprotective effects. Clinical Medicine Insights: Cardiology. 2014.
Written by the Macropus Peptides technical team for in-vitro laboratory research reference. Not medical advice; products are not for human or veterinary use and are sold to buyers aged 18 and over.