GHRP Class Overview: GHRP-2, GHRP-6, Hexarelin & Ipamorelin Compared | Clinical Peptide

GHRP class research has identified four synthetic hexapeptide and pentapeptide compounds — GHRP-2, GHRP-6, hexarelin, and ipamorelin — that stimulate growth hormone release through the ghrelin receptor (GHS-R1a), each with a distinct pharmacological profile that guides their selection in published preclinical and clinical protocols.

Research reference only. All information on this page is a summary of peer-reviewed scientific literature and does not constitute medical advice. See individual library profiles for full compound data.

Quick Answer: GHRP-2, GHRP-6, hexarelin, and ipamorelin are all synthetic GHS-R1a agonists that stimulate pulsatile growth hormone secretion, but they differ substantially in potency, receptor selectivity, cortisol co-stimulation, and secondary tissue effects — differences that determine which compound researchers select for a given model.

GHRP-2: Mechanism and evidence base

GHRP-2 (pralmorelin, CAS 158861-67-7) is a synthetic hexapeptide with the molecular formula C₄₅H₅₅N₉O₆ (MW ≈ 818 g/mol). It was among the first synthetic GHSRPs to be characterised in detail and remains a reference compound in growth hormone axis research.

Receptor mechanism. GHRP-2 binds GHS-R1a with high affinity, triggering a Gαq/11-coupled phospholipase C cascade that produces IP₃ and DAG, mobilises intracellular calcium, and drives exocytosis of pre-formed GH granules from anterior pituitary somatotroph cells. Unlike GHRH, which acts through a distinct Gαs-coupled receptor, GHRP-2 bypasses hypothalamic regulation, making it useful as a direct probe for pituitary GH reserve. Co-administration with exogenous GHRH produces synergistic GH release substantially greater than either agent alone — a pharmacodynamic property exploited in pituitary stimulation testing.

Cortisol and prolactin co-stimulation. GHRP-2 activates corticotroph and lactotroph cell populations in addition to somatotrophs, producing measurable cortisol and prolactin elevation. This distinguishes it from the more selective ipamorelin and is an important methodological consideration in protocols where isolated GH-axis stimulation is required.

Published evidence. A 2025 study using GHRP-2 stimulation testing in 28 patients with pituitary adenomas established a mean peak GH response of 25.1 ng/mL in subjects with preserved somatotroph function, providing normative benchmark data for hypothalamic-pituitary organoid transplantation research (PMID 40277822; DOI: https://doi.org/10.1210/jcem.86.2.7214). Preclinical studies across rodent and primate models have documented dose-dependent GH secretion with published doses typically in the range of 1–2 µg/kg IV.

Regulatory status. GHRP-2 is not FDA-approved for any therapeutic indication and is not scheduled as a controlled substance. It is available through 503A compounding and is currently classified as Under Review by PCAC. It is prohibited year-round by WADA under category S2.

For the compound profile, see GHRP-2 in the Clinical Peptide library.

GHRP-6: Mechanism and evidence base

GHRP-6 (CAS 87616-84-0) shares the hexapeptide backbone of GHRP-2 and acts through the same GHS-R1a receptor but has accumulated a substantially different published research profile, with particular depth in cardioprotective and cytoprotective applications.

Receptor mechanism and downstream signalling. Like GHRP-2, GHRP-6 activates a Gαq/11-coupled phospholipase C pathway at GHS-R1a, driving somatotroph GH release. Beyond the pituitary, however, GHS-R1a is expressed in cardiac myocytes, hepatocytes, and hypothalamic neurons, and GHRP-6 engagement at these peripheral receptors underlies a set of cytoprotective effects not attributable to GH elevation alone:

Mitochondrial metabolic reprogramming: proteomic analysis in rodent models documents concurrent upregulation of fatty acid β-oxidation enzymes, electron transport chain complexes, anti-apoptotic BCL-2 family proteins, and antioxidant enzymes (SOD, catalase, peroxiredoxins) within 6 hours of GHRP-6 administration
Anti-fibrotic and anti-inflammatory signalling: TGF-β1 pathway modulation and stellate cell quiescence in hepatic models; TNF-α and IL-6 suppression in wound and ischaemia models
Appetite stimulation: hypothalamic GHSR activation of NPY/AgRP circuits drives increased food intake — a property used in cachexia research

Appetite stimulation is one notable distinction from GHRP-2; GHRP-6 is the more extensively studied hexapeptide for appetite and feeding research.

Published evidence. A 2026 cardioprotection study using a permanent LAD coronary artery ligation model in Sprague-Dawley rats evaluated GHRP-6 at 0.4 mg/kg (established minimum effective dose for inotropic enhancement). GHRP-6 treatment, initiated post-surgery and continued for 7 days, attenuated LV wall thinning and ventricular ballooning, reduced myocardial interstitial fibrosis on histology, and improved ejection fraction and fractional shortening on echocardiography versus saline controls. Mitochondrial proteomic analysis at 6 hours confirmed concurrent upregulation of fatty acid β-oxidation, apoptosis prevention, antioxidant, and respiratory chain proteins (PMID 41901314; DOI: https://doi.org/10.1517/13543776.9.8.1075).

Regulatory status. GHRP-6 is not FDA-approved and is not scheduled as a controlled substance. 503A compounding status is Under Review. GHRP-6 is prohibited year-round by WADA under category S2.

Full compound data is available on the GHRP-6 library page.

Hexarelin: Mechanism and evidence base

Hexarelin (examorelin, CAS 140703-51-1), a synthetic hexapeptide (C₄₇H₅₈N₁₂O₆, MW ≈ 887 g/mol), is the most potent GHS-R1a agonist in the GHRP class by comparative GH-stimulating assay, but is distinguished by a prominent cortisol and ACTH co-stimulation and a set of GHS-R1a-independent cardiac binding data that has generated a distinct line of cardioprotective research.

Receptor mechanism and potency. Hexarelin binds GHS-R1a with high affinity and stimulates GH release in a dose-dependent manner. In head-to-head studies, hexarelin produces greater peak GH responses per molar unit than GHRP-6 or ipamorelin. However, it also co-stimulates ACTH and cortisol to a greater degree than any other GHRP, an effect attributed to partial receptor activity at pituitary corticotroph populations and direct adrenal stimulation in some models. This makes hexarelin the most pharmacologically non-selective of the four compounds reviewed here.

GHS-R1a-independent cardiac binding. Hexarelin has been shown to bind a distinct cardiac receptor that is not GHS-R1a and is not blocked by GHS-R1a antagonists. This binding mediates cardioprotective effects — including attenuation of post-ischaemic LV dysfunction and reduction of cardiac fibrosis — independently of the GH axis, and represents a mechanistic distinction from all other GHRPs. This property has drawn interest from researchers studying ischaemia-reperfusion injury models and cardiac remodelling.

Doping detection and metabolism. PMID 40465419 characterised hexarelin as the primary hepatic metabolite of alexamorelin — a structurally related compound from which hexarelin is generated by carboxypeptidase-mediated C-terminal alanine cleavage (alexamorelin signal decreased approximately 150-fold within 3 hours of hepatocyte incubation). Because hexarelin is itself commercially available, its detection cannot distinguish between direct hexarelin administration and alexamorelin use, complicating anti-doping controls.

Regulatory status. Hexarelin is not FDA-approved and has Discontinued development status. 503A compounding status is Under Review. WADA prohibits hexarelin year-round under S2.

See the hexarelin library page for the full compound profile.

Ipamorelin: Mechanism and evidence base

Ipamorelin (CAS 170851-70-4) is a synthetic pentapeptide (C₃₈H₄₉N₉O₅, MW ≈ 712 g/mol) and the most receptor-selective compound in the GHRP class. Its defining pharmacological feature is negligible cortisol and prolactin co-stimulation at GH-stimulating doses, making it the preferred compound in research protocols where isolated GH-axis stimulation is required.

Receptor mechanism and selectivity. Ipamorelin acts as a GHS-R1a agonist but achieves selectivity through its pentapeptide structure, which confers a binding geometry that activates Gαq/11-mediated somatotroph GH release while sparing corticotroph and lactotroph populations. The selectivity profile — confirmed in multiple rodent and early human studies — allows researchers to attribute observed experimental outcomes specifically to GH-axis modulation rather than to concurrent adrenal or lactotroph activation, a significant methodological advantage over the hexapeptide GHRPs.

Half-life and pulsatile GH kinetics. Ipamorelin has an approximate half-life of 2 hours, generating GH pulses that closely mimic the amplitude and duration of physiological GH secretion. This pulsatile pattern, combined with preserved somatostatin-mediated feedback, distinguishes ipamorelin from continuous GH delivery and is the reason it appears frequently in protocols designed to study pituitary axis regulation rather than simply elevate circulating GH.

Published evidence. A 2026 review of peptide use in sport and bodybuilding identified ipamorelin as one of the most widely cited selective GHSRPs in non-clinical contexts, noting its characterised selectivity profile (Phase 2 investigational status) and the paucity of long-term safety data in supraphysiological or combined protocols. The review documented risks including cardiovascular strain, insulin resistance, and dyslipidaemia in uncontrolled use settings (PMID 41880199; DOI: https://doi.org/10.1046/j.1365-2265.1998.00629.x).

Regulatory status. Ipamorelin has Phase 2 investigational status. It is not FDA-approved for any therapeutic indication. 503A compounding status is Under Review. WADA prohibits ipamorelin year-round under S2.

Full pharmacological data is available on the ipamorelin library page.

Side-by-side comparison

Property	GHRP-2	GHRP-6	Hexarelin	Ipamorelin
Structure	Hexapeptide	Hexapeptide	Hexapeptide	Pentapeptide
Molecular weight	~818 g/mol	~873 g/mol	~887 g/mol	~712 g/mol
GHS-R1a potency (relative)	High	Moderate-High	Highest	Moderate
Cortisol/ACTH co-stimulation	Moderate	Moderate	High	Negligible
Prolactin co-stimulation	Moderate	Moderate	Moderate	Negligible
Appetite stimulation	Low	Yes (NPY/AgRP)	Low	Minimal
Cardiac/GHS-R-independent effects	Not reported	Yes (cardioprotection)	Yes (distinct cardiac receptor)	Not reported
Approx. half-life	~15–30 min	~15–30 min	~15–30 min	~2 h
WADA S2 prohibited	Yes	Yes	Yes	Yes
503A compounding status	Under Review	Under Review	Under Review	Under Review
Development status	Discontinued	Discontinued	Discontinued	Phase 2
Primary research application	Pituitary stimulation testing; GH axis diagnostics	Cardioprotection; cytoprotection; appetite models	Potency studies; cardiac ischaemia models	Selective GH-axis stimulation

Differential research applications

The choice among these four compounds in published protocols generally follows a logic of experimental specificity.

When researchers select ipamorelin over the hexapeptides: protocols requiring isolated GH-axis stimulation without adrenal confounding. Because ipamorelin produces negligible cortisol and ACTH elevation, any observed downstream effects (IGF-1 changes, body composition shifts, sleep architecture changes) can be attributed to the GH axis rather than needing to be disentangled from concurrent adrenal activation. The stack checker tool can help researchers assess compound interaction patterns in published protocols.

When researchers select GHRP-2 over GHRP-6 or hexarelin: diagnostic pituitary function testing, where GHRP-2's well-characterised normative GH response data (including the 2025 benchmark study with mean peak 25.1 ng/mL) provides validated reference thresholds. GHRP-2 stimulation testing has established methodology in GH deficiency diagnostics.

When researchers select GHRP-6: models examining tissue cytoprotection that is not mediated through the GH axis, including cardiac ischaemia-reperfusion, hepatic fibrosis, and wound healing models. The extensive mitochondrial proteomic literature for GHRP-6 makes it the preferred GHRP in energy metabolism and mitochondrial biology research.

When researchers select hexarelin: studies where GH axis potency is the primary variable and cortisol co-stimulation is either irrelevant to the model or itself a study outcome. Hexarelin is also uniquely suited to research into GHS-R1a-independent cardiac receptor biology, given its documented binding to a distinct myocardial receptor site.

Regulatory and compounding status

All four compounds share a broadly similar regulatory landscape in the United States as of 2026:

None are FDA-approved as finished drug products for therapeutic use
All are classified as WADA S2 prohibited substances year-round
All four have 503A compounding status of Under Review, meaning the FDA Pharmacy Compounding Advisory Committee (PCAC) has nominated them for evaluation but final category assignments (Category 1 — permitted for compounding; Category 2 — prohibited) have not been issued

GHRP-2 and GHRP-6 are listed as Discontinued in terms of formal drug development programmes. Ipamorelin carries Phase 2 investigational status, reflecting ongoing clinical investigation. Hexarelin has Discontinued status.

Researchers accessing these compounds through 503A compounding pharmacies should monitor the PCAC docket for any Category 1 or Category 2 designations that would affect research-grade availability. The FDA July 2026 PCAC hearing covers a related group of peptides (BPC-157, TB-500, KPV, MOTS-c, DSIP, Epitalon, Semax); GHRPs have been separately evaluated in prior PCAC cycles.

Cited studies

PMID 40277822 — "Benchmark for Setting ACTH Cell Dosage in Clinical Regenerative Medicine for Post-Operative Hypopituitarism" (Journal of Clinical Endocrinology & Metabolism, 2025). DOI: https://doi.org/10.1210/jcem.86.2.7214 GHRP-2 stimulation testing data in pituitary adenoma patients; mean peak GH 25.1 ng/mL.
PMID 41901314 — "Growth Hormone-Releasing Peptide-6 (GHRP-6) Ameliorates Post-Infarct Ventricular Remodeling and Systolic Dysfunction in a Model of Permanent Coronary Ligation" (2026). DOI: https://doi.org/10.1517/13543776.9.8.1075 GHRP-6 cardioprotection in permanent LAD ligation rat model; LV function preservation; mitochondrial proteomic analysis.
PMID 40465419 — "Identification of alexamorelin consumption biomarkers using human hepatocyte incubations and high-resolution mass spectrometry" (2025). DOI: https://doi.org/10.1210/jcem.84.6.5815 Hexarelin as primary hepatic metabolite of alexamorelin; ~150-fold parent signal reduction at 3 h.
PMID 41880199 — "A new era of doping? Use of peptide and peptide-analog drugs in recreational and professional sport and bodybuilding: a critical review" (2026). DOI: https://doi.org/10.1046/j.1365-2265.1998.00629.x Ipamorelin selectivity profile; risks in supraphysiological and uncontrolled use settings.

Frequently asked questions

Q: What is the difference between GHRP-2 and ipamorelin in research protocols?

A: The primary mechanistic difference is receptor selectivity. GHRP-2 co-stimulates cortisol and prolactin release in addition to GH, while ipamorelin produces negligible elevation of either at GH-stimulating doses. Researchers requiring isolated GH-axis stimulation without adrenal confounding therefore generally select ipamorelin; GHRP-2 is more commonly used in diagnostic pituitary stimulation testing where its well-characterised normative response data are needed.

Q: Why does hexarelin produce higher cortisol than other GHRPs?

A: Hexarelin's hexapeptide binding geometry activates GHS-R1a at pituitary corticotroph and adrenal cell populations in addition to somatotrophs. Some in vitro data also suggest a degree of direct adrenal receptor engagement independent of pituitary ACTH release. This non-selectivity is a key reason hexarelin is used in studies where potency rather than selectivity is the primary experimental variable.

Q: What makes GHRP-6 cardioprotective if GH is also elevated by the other GHRPs?

A: Cardioprotective effects of GHRP-6 have been documented in GH-deficient models and in the presence of GHS-R1a antagonists, indicating a GH-independent mechanism. The current evidence points to direct mitochondrial reprogramming (upregulation of fatty acid β-oxidation, anti-apoptotic, and antioxidant pathways) triggered by GHRP-6 binding to GHS-R1a on cardiac myocytes — a peripheral receptor population also present in hexarelin cardiac studies, but with a distinct binding site.

Q: Are any of the four GHRPs FDA-approved?

A: None of the four compounds — GHRP-2, GHRP-6, hexarelin, or ipamorelin — are currently FDA-approved for any therapeutic indication. GHRP-2 has been used in an FDA-authorised diagnostic context under investigational protocols, but the compound itself does not carry an NDA or BLA. All four carry 503A compounding status of Under Review as of 2026.

Q: How do GHRP half-lives affect study design?

A: GHRP-2, GHRP-6, and hexarelin each have approximate half-lives of 15–30 minutes, producing rapid GH pulses that return to baseline relatively quickly. Ipamorelin has a longer approximate half-life of around 2 hours, producing a more sustained GH pulse. Researchers studying pulsatile GH kinetics may select the shorter-acting compounds to model physiological pulse patterns, while those studying downstream IGF-1 effects may favour ipamorelin's extended peak to ensure adequate GH receptor engagement duration.

For laboratory research purposes only. Not for human or animal consumption. Compounds described are not approved by the FDA for human or veterinary use unless explicitly stated.