Before anyone knew ghrelin existed, an endocrinologist in New Orleans found that an odd little hexapeptide could make the pituitary release growth hormone. That peptide, GHRP-6, and its successors GHRP-2 and hexarelin, sent researchers looking for the receptor they acted on, and that search ended with the discovery of ghrelin itself.
This guide compares the three, explains how they differ from ipamorelin and the GHRH analogues, and covers what to check before ordering any of them in Canada.
The short answer
- GHRP-6, GHRP-2 and hexarelin are synthetic six-residue peptides that release growth hormone through the ghrelin receptor, GHS-R1a, not the GHRH receptor.
- GHRP-6 came first, described by Cyril Bowers’ group at Tulane University in 1984. It grew out of work on modified enkephalin peptides.
- The hunt for their receptor led to GHS-R1a being cloned in 1996, and to ghrelin, its natural hormone, being discovered in 1999.
- GHRP-2 (pralmorelin) is approved in Japan as a diagnostic test for growth hormone deficiency. Hexarelin also binds CD36, a receptor studied in the heart.
- All three are prohibited in sport. Research-grade versions are laboratory reagents.
The GHRP family
Three hexapeptides, one shared tail. Highlighted beads show the four C-terminal residues all three have in common.
GHRP-6
- His
- D-Trp
- Ala
- Trp
- D-Phe
- Lys
- NH₂
GHRP-2 (pralmorelin)
- D-Ala
- D-2Nal
- Ala
- Trp
- D-Phe
- Lys
- NH₂
Hexarelin
- His
- D-2MeTrp
- Ala
- Trp
- D-Phe
- Lys
- NH₂
- Receptor
- GHS-R1a, the ghrelin receptor (hexarelin also binds CD36)
- First described
- GHRP-6, 1984, Cyril Bowers’ group at Tulane University
- Approvals
- GHRP-2 only, as a diagnostic in Japan (GHRP Kaken 100)
- Research themes
- Growth hormone release, appetite, cardioprotection models
Where the evidence stands
- Cell studies
- Animal studies
- Human studies
- Approved treatments
GHRP-2’s approval covers diagnostic testing only. None is approved as a treatment.
From enkephalins to ghrelin
The GHRP story is a rare case of a synthetic drug leading scientists to a hormone the body already makes.
- Early 1980sCyril Bowers, an endocrinologist at Tulane University, notices that chemically modified analogues of enkephalin, a brain opioid peptide, can release growth hormone from pituitary cells.
- 1984His group describes GHRP-6, His-D-Trp-Ala-Trp-D-Phe-Lys-NH₂, which releases growth hormone in several species, including humans.
- Late 1980s–1990sChemistry built on GHRP-6 produces GHRP-1, GHRP-2 and hexarelin. All act through a mechanism separate from GHRH.
- 1996A team at Merck clones the receptor these peptides use, the growth hormone secretagogue receptor, GHS-R1a. Its natural ligand is unknown.
- 1999Japanese researchers identify that ligand: ghrelin, a 28-amino-acid hormone made in the stomach.
Because the receptor is the same one ghrelin uses, GHRPs act like ghrelin in more ways than growth hormone release. GHRP-2, for example, reliably increases hunger and food intake in people.
How the three compare
| Feature | GHRP-6 | GHRP-2 | Hexarelin |
|---|---|---|---|
| Generation | First (1984) | Second | Second |
| Receptors | GHS-R1a | GHS-R1a | GHS-R1a and CD36 |
| Other hormones | Raised ACTH and cortisol in a 1998 swine comparison | Raised ACTH and cortisol in the same comparison | Reported to raise cortisol and prolactin more than GHRP-2 |
| Regulatory status | Not approved | Diagnostic approval in Japan | Not approved |
| Mass | About 873 g/mol | About 818 g/mol | About 887 g/mol |
Hexarelin is GHRP-6 with a methyl group added to its D-tryptophan, which is why the two masses differ by about 14 g/mol. GHRP-2 swaps the first two residues for D-alanine and D-2-naphthylalanine.
GHRP-6, GHRP-2 and hexarelin, each with a batch-matched COA.
Browse growth and signallingHexarelin and the CD36 twist
Hexarelin has a second receptor. Besides GHS-R1a, it binds CD36, a scavenger receptor on heart and blood-vessel cells. In isolated heart studies, hexarelin increased coronary perfusion pressure in a dose-dependent way, and that effect disappeared in hearts from CD36-knockout mice. That finding opened a line of cardiac research on GHRPs that has nothing to do with growth hormone, and it makes hexarelin a useful tool for separating the two receptor pathways.
Where ipamorelin fits
Ipamorelin was designed later, at Novo Nordisk, partly to fix a weakness of the GHRPs. In the 1998 swine study that introduced it, GHRP-6 and GHRP-2 raised ACTH and cortisol alongside growth hormone, while ipamorelin did not, even at doses far above those needed for growth hormone release. That selectivity is why ipamorelin became a reference compound. It is often paired with GHRH analogues; see CJC-1295 vs ipamorelin for that pairing and sermorelin and tesamorelin for the GHRH side.
GHRP-6The first-generation hexapeptideView product and COA
GHRP-2Pralmorelin, second generationView product and COA
HexarelinGHS-R1a plus CD36View product and COA
IpamorelinThe selective successorView product and COA
Sourcing GHRPs in Canada
These three are small and similar, so identity testing does most of the work. Before ordering, check that:
- The mass matches the peptide on the label. At about 873, 818 and 887 g/mol, GHRP-6, GHRP-2 and hexarelin are easy to tell apart by mass spectrometry. See HPLC vs mass spectrometry.
- The COA matches your lot. How to read a certificate of analysis explains what to look for.
- Purity is reported by HPLC. Purity versus net peptide content covers the fine print.
- Storage is cold, dry and dark. Our peptide storage guide has the details.
The World Anti-Doping Agency’s 2026 Prohibited List bans growth hormone-releasing peptides, including GHRP-2, GHRP-6 and hexarelin, at all times. Canadian athletes are tested under the Canadian Anti-Doping Program, which applies that list.
Research use only. GHRP-6, GHRP-2 and hexarelin from Pure Peptides Canada are laboratory reagents. They are not approved drugs in Canada, are not for human or veterinary use, and nothing in this article is dosing or medical guidance.
Frequently asked questions
What are GHRPs?
Growth hormone-releasing peptides (GHRPs) are small synthetic peptides, including GHRP-6, GHRP-2 and hexarelin, that stimulate growth hormone release by activating the ghrelin receptor, GHS-R1a. They act through a different receptor from GHRH and its analogues.
What is the difference between GHRP-6 and GHRP-2?
GHRP-6 is the first-generation hexapeptide described in 1984. GHRP-2 is a second-generation analogue with different first two residues. GHRP-2, as pralmorelin, is approved in Japan as a diagnostic test for growth hormone deficiency, while GHRP-6 has never been approved.
What is hexarelin?
Hexarelin is GHRP-6 with a methyl group added to its D-tryptophan. Besides the ghrelin receptor, it binds CD36, a receptor on heart and blood-vessel cells, which has made it a tool in cardiac research.
How do GHRPs differ from ipamorelin?
All act on the ghrelin receptor, but in the 1998 swine study that introduced ipamorelin, GHRP-6 and GHRP-2 also raised ACTH and cortisol, while ipamorelin did not. That selectivity is ipamorelin’s defining feature.
Are GHRPs approved in Canada?
No. GHRP-2 is approved only in Japan, and only as a diagnostic agent. Research-grade GHRPs sold by Pure Peptides Canada are laboratory reagents that are not for human use.
Are GHRPs banned in sport?
Yes. The World Anti-Doping Agency’s 2026 Prohibited List bans growth hormone-releasing peptides, including GHRP-2, GHRP-6 and hexarelin, at all times.
The GHRP family, tested batch by batch
GHRP-6, GHRP-2 and hexarelin with independent COAs, tracked delivery across Canada and pricing in Canadian dollars.
References
- Bowers CY, et al. 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;114:1537–1545.
- Howard AD, et al. A receptor in pituitary and hypothalamus that functions in growth hormone release. Science. 1996;273:974–977.
- Kojima M, et al. Ghrelin is a growth-hormone-releasing acylated peptide from stomach. Nature. 1999.
- Berlanga-Acosta J, et al. Synthetic growth hormone-releasing peptides (GHRPs): a historical appraisal of the evidences supporting their cytoprotective effects. 2017. PubMed Central
- World Anti-Doping Agency. The 2026 Prohibited List, section S2. WADA
For laboratory research use only. Not for human or veterinary use. This article summarizes published research for educational purposes and is not medical advice. Nothing here is intended to diagnose, treat, cure or prevent any disease.