GHRP-2, GHRP-6, hexarelin and ipamorelin: GH secretagogues compared

GHRP-2, GHRP-6, hexarelin and ipamorelin are four peptides that the research literature describes as secretagogues of the ghrelin receptor GHS-R1a. All of them stimulate growth hormone (GH) release in in vitro and animal models, but they differ in structure, selectivity profile and how strongly they affect other hormonal axes. This overview sorts out those differences and shows what to check when planning work with these reagents.

All four are available at MOLEVIA as research peptides and reagents (Research Use Only). Every batch comes with purity of 99% or higher (HPLC), mass confirmed by MS.

The GHS-R1a receptor: a common starting point

The GHS-R1a receptor, also called the ghrelin receptor, belongs to the family of G protein-coupled receptors. Its natural ligand is ghrelin, a hormone produced mainly in the stomach. GHRP-class secretagogues mimic ghrelin’s action at the pituitary and hypothalamus. Binding to the receptor starts intracellular signalling, which in models leads to increased GH secretion.

For a researcher, the key point is that this receptor is the shared target of all four compounds. The differences do not come from a different receptor. They come from how each peptide binds, how long it sustains receptor activation and which side signals appear in a given model.

Molecular structure

All four compounds are short synthetic peptides. GHRP-2, GHRP-6 and hexarelin are hexapeptides with six amino acid residues, while ipamorelin is a pentapeptide. Most of them carry D-amino acids and a C-terminal amide. These modifications increase resistance to proteolytic enzymes, which makes the peptides easier to handle in in vitro work.

GHRP-2

A hexapeptide that opens with a D-alanine, with a D-2-naphthylalanine in the second position. The molecular mass is about 817.9 g/mol. It is one of the more frequently studied GH secretagogues in this group and serves as a convenient reference point in comparisons.

GHRP-6

A hexapeptide with a histidine at the N-terminus and two tryptophan residues in the sequence. The molecular mass is about 873 g/mol. It is one of the first well-described GH secretagogues in this family, which is why it appears in most reviews as a benchmark.

Hexarelin

A hexapeptide with a histidine at the N-terminus and a modified tryptophan (D-2-methyl-tryptophan) in the second position. The molecular mass is about 887 g/mol. Beyond GHS-R1a, the literature describes its link to the CD36 receptor in cardiac models. This thread sets hexarelin apart from the other compounds in this comparison.

Ipamorelin

A pentapeptide with the sequence Aib-His-D-2Nal-D-Phe-Lys-NH2 and a molecular mass of about 711.9 g/mol. The literature presents it as a compound with a narrower activity profile than the hexapeptides in this group. It has also been studied in clinical trials, a fact recorded in the published literature, and at MOLEVIA it remains a laboratory research reagent.

Selectivity: prolactin, cortisol and appetite in models

The parameters compared most often are the effects on prolactin, cortisol and food intake. These are the areas where differences between the compounds are most visible in the literature.

Prolactin

In comparisons described in the literature, GHRP-6 and hexarelin were linked to a more pronounced rise in prolactin than ipamorelin. GHRP-2 sits in between. For this reason ipamorelin is often chosen in projects where the goal is to isolate the GH axis from prolactin-related signals.

Cortisol

A similar pattern was reported for cortisol. Hexarelin and GHRP-6 raised cortisol levels in some studies, while ipamorelin showed the least pronounced effect in direct comparisons. This parameter matters in stress models because it is part of the hypothalamic-pituitary-adrenal axis.

Appetite in models

GHRP-6 is frequently cited as a secretagogue that stimulates food intake in rodent models. This fits the biology of ghrelin, the natural hunger signal. The other compounds have been examined in this context less often or with less consistent results. These observations come from animal models only and belong to mechanistic research.

Desensitisation

Long exposures in vivo have been reported to reduce the response to hexarelin, a phenomenon known as receptor desensitisation. For that reason, long-term projects depend on planning the duration of the experiment and keeping the model response under steady control.

Comparison table

Feature	GHRP-2	GHRP-6	Hexarelin	Ipamorelin
Peptide type	hexapeptide	hexapeptide	hexapeptide	pentapeptide
Receptor	GHS-R1a	GHS-R1a	GHS-R1a	GHS-R1a
Mass (g/mol)	817.9	873	887	711.9
CAS number	158861-67-7	87616-84-0	140703-51-1	170851-70-4
Prolactin in comparisons	moderate	pronounced	pronounced	low
Cortisol in comparisons	moderate	pronounced	pronounced	low
Appetite in models	studied	strongly described	studied	less described
Additional thread	none	none	CD36 receptor in cardiac models	none
Status	research reagent	research reagent	research reagent	research reagent

Working in the laboratory

Lyophilised reagents need storage at low temperature, in a sealed container, away from light and moisture. Before a study starts, check the HPLC purity and the agreement between the mass and the MS result for your batch. Comparisons between compounds only make sense when all of them are tested under the same conditions and with material from the same analytical series.

When you put results side by side, keep three rules in mind. First, describe each compound separately, with its own receptor profile. Second, results from animal models do not transfer automatically to other species. Third, prolactin and cortisol readouts depend on the design of the experiment, so the same peptide can look different in different labs.

Ordering from MOLEVIA

Full data for each compound is on the product pages: GHRP-2, GHRP-6, hexarelin and ipamorelin. More compounds from this group are listed in the GH axis category.

• Same-day dispatch for orders placed by 2:00 pm on business days.
• InPost parcel lockers in Poland: next business day delivery.
• DPD across Europe: 2 to 4 business days, shipping to 29 countries.
• Free shipping on orders from 75 EUR, 65 GBP or 80 USD.
• Automatic volume discounts: 5% for 2 pieces, 10% for 3 pieces, 15% for 5 pieces.
• For orders of 50 EUR (40 GBP, 55 USD) or more that include a peptide vial, 10 ml of bacteriostatic water free of charge.
• Pay online by card, Apple Pay, Google Pay or BLIK (PLN only).

Key takeaways

• GHRP-2, GHRP-6, hexarelin and ipamorelin all act on the same GHS-R1a receptor.
• Ipamorelin is a pentapeptide and, in comparisons, shows the calmest profile for prolactin and cortisol.
• GHRP-6 and hexarelin are more often linked to a pronounced rise in prolactin and cortisol.
• GHRP-6 is frequently cited in appetite research in animal models.
• Hexarelin has an additional thread, the CD36 receptor, described in cardiac models.
• A reliable comparison requires purity of 99% or higher (HPLC) and confirmed mass (MS).