Hexarelin: The Most Potent GHRP, and Why It Fades

At a Glance

Hexarelin is the GHRP that gives the biggest growth hormone pulse, and the clearest demonstration that a big pulse is not the same as a useful outcome. It has a better human data set than most peptides in this family: a formal dose-response study, a four-route comparison, a 16-week chronic study and small cardiac studies in real patients.

The honest verdict comes from that 16-week study. Twice-daily hexarelin halved its own GH response by week 16, and across those four months IGF-1, IGFBP-3, total body fat, lean mass and bone mineral density all failed to change significantly. That is the most direct test anyone has run of the premise that amplifying GH pulses with a GHRP reshapes the body, and the answer was no, at least at that dose and duration.

What keeps hexarelin interesting is the second receptor. CD36 binding gives it cardiac actions that do not depend on growth hormone at all, with a handful of small human studies behind them. That is a different and arguably more promising line of research than body composition, and nobody took it to a proper trial.

How it works

GHS-R1a, the ghrelin receptor. Hexarelin is a methylated derivative of GHRP-6, a change that increases potency and metabolic stability. It stimulates GH release from pituitary somatotrophs through the ghrelin receptor and reduces somatostatin tone at the hypothalamic level, so GH rises in a pulse that still respects feedback. Combination with GHRH is synergistic, more than the sum of the two alone (Massoud 1996).

Non-selectivity at the pituitary. At GH-releasing doses hexarelin also raises prolactin, ACTH and cortisol. In the dose-response study the prolactin curve plateaued at about 180% above baseline with an ED50 of 0.39 mcg/kg, close to the ED50 of 0.48 mcg/kg for GH, which means the two effects cannot be separated by dose (Massoud 1996). The hormonal response also shifts with age: GH responsiveness falls while the ACTH and cortisol response follows a different age curve (Arvat 1997b).

CD36 in the heart. Radiolabelled hexarelin binding in rat cardiac membranes identified an 84 kDa protein that turned out to be CD36, expressed in cardiomyocytes and microvascular endothelium. Activating it in perfused hearts raised coronary perfusion pressure dose-dependently, and the effect was absent in CD36-null mice (Bodart 2002). This is why hexarelin has a cardiovascular literature that ipamorelin does not (Mao 2014).

Desensitisation. Repeated GHS-R1a stimulation downregulates the GH response. Hexarelin is the compound in which this was measured most carefully in humans, over 16 weeks (Rahim 1998).

What the evidence shows

Human data

Potency and routes. Twelve healthy young volunteers received hexarelin by four routes. At 1 mcg/kg intravenously the GH area under the curve was about twice that of 1 mcg/kg GHRH (3,175 versus 1,544 mcg/min/L); 2 mcg/kg produced a further increase; the response was highly reproducible on repeat testing; and subcutaneous dosing at 1.5 and 3 mcg/kg was dose-dependent. Intranasal (20 mcg/kg) and oral (20-40 mg) dosing also worked, at far higher doses (Ghigo 1994).

Dose-response and hormone selectivity. In healthy adult men the GH dose-response curve plateaued at 1.0 mcg/kg intravenously with an ED50 of 0.48 mcg/kg; prolactin plateaued at the same dose with an ED50 of 0.39 mcg/kg, and cortisol showed a step increase (Massoud 1996). A head-to-head study with GHRP-2 found similar GH potency between the two, with modest prolactin, ACTH and cortisol rises for both (Arvat 1997).

Sixteen weeks of twice-daily use. This is the study that matters most for anyone considering hexarelin for body composition. Adults received 1.5 mcg/kg subcutaneously twice daily for 16 weeks. The GH area under the curve in response to a test dose fell from 19.1 mcg/L·h at baseline to 12.3 at week 4 and 10.5 at week 16, then rose back to 19.4 four weeks after stopping. Serum IGF-1 and IGFBP-3 did not change significantly across the 20 weeks. Of the bone markers, only type I collagen C-terminal propeptide rose. Total body fat, lean body mass and bone mineral density were unchanged (Rahim 1998).

Cardiac studies. In seven men with GH deficiency and nine controls, intravenous hexarelin raised left ventricular ejection fraction in both groups (from 50% to 57% in the deficient group) without changing catecholamines, mean blood pressure or cardiac output. The GH response in the deficient group was negligible, which separates the cardiac effect from GH (Bisi 1999). In 13 patients with severe left ventricular dysfunction, hexarelin raised ejection fraction in ischaemic cardiomyopathy (22.6% to 26.2%) but not in dilated cardiomyopathy, while raising GH similarly in both (Imazio 2002). Small, acute, unblinded, and still the most interesting thing about this molecule.

Animal data, labelled as such

CD36-mediated protection appears across ischaemia-reperfusion models, with reduced apoptosis and preserved function in rodents, and the GHRP class as a whole carries a substantial animal cytoprotection literature (Berlanga-Acosta 2017). None of it has been tested against a clinical endpoint in humans.

What is missing

No randomised trial of hexarelin for any clinical outcome, cardiac or otherwise. The one chronic human study found no change in body composition. The current narrative review of this class lists hexarelin among the compounds whose performance and recomposition claims rest on extrapolation (Dominikowski 2026).

Dosing

For informational purposes only — this summarises doses used in research and practice; it is not a prescription or individual medical advice.

Titration as it is actually done. One 100 mcg injection daily for the first week or two is the usual starting point, because hexarelin’s hormonal side effects are the most noticeable in this class. People who tolerate it add a second and sometimes a third daily injection. Protocol writers describe hexarelin as a compound for people who already know how they respond to ipamorelin or GHRP-2, which is reasonable advice given how closely the GH and prolactin dose-response curves overlap.

On and off cycle. Cycling here is not folklore. The 16-week human study showed the GH response halving by week 16 and recovering fully four weeks after stopping (Rahim 1998). Practice protocols mirror that with 8-12 weeks on and 4-6 weeks off, and some rotate to ipamorelin during the off block.

Reconstitution, storage and technique are in the peptide injection guide. Broader cycle design is in peptide cycling protocols.

What people report: what works and what doesn’t

Sources: the aggregated community data set (Peptide Protocol Wiki, 60 reports), a second protocol compilation (Peptide DB), the patterns catalogued in the peer-reviewed review of this class (Dominikowski 2026), and the human studies above. Patterns, not proof.

Reported to work

• The strongest GH-type symptoms in this family within the first two weeks: deep sleep, fluid retention, sometimes more sweating. Consistent with hexarelin being the most potent GH releaser here.
• Moderate hunger, less than GHRP-6, more than ipamorelin.
• A clear fade in effect by weeks 4 to 8. This is the one anecdote in this whole area that matches a published human measurement almost exactly.

Mixed or unclear

• Recovery and connective tissue. Described, but confounded by stacking, since most people run hexarelin alongside a GHRH analogue.
• The cardiac angle. A minority use low-dose hexarelin specifically for the CD36 pathway. There is no human protocol for that, the supporting human studies were single intravenous doses, and no reported outcome can be verified.
• Whether rotating GHRPs prevents desensitisation. Plausible, never tested.

Reported not to work, or disappointing

• Lasting body-composition change. This matches the trial data: 16 weeks of twice-daily hexarelin produced no significant change in fat mass, lean mass or bone density (Rahim 1998).
• Running it continuously. The most common complaint is that it stops delivering after a month or two, and the published data say that is exactly what should happen.
• Side effects people stop for: lethargy, low mood or breast tenderness attributed to prolactin, water retention, hand tingling, and in those who test, mildly raised cortisol or prolactin. Mild hypercortisolaemia or hyperprolactinaemia in someone using a GHRP is a recognised class effect, and retesting after a washout before imaging the pituitary is the sensible sequence (Dominikowski 2026).

What a properly designed trial would need to show: for the cardiac claim, a randomised controlled trial in ischaemic cardiomyopathy with ejection fraction and functional endpoints over months rather than minutes. For the body-composition claim, something better than the negative 16-week result already published.

Safety and side effects

Observed in humans. Flushing, transient drowsiness, sweating and injection-site reactions. Prolactin, ACTH and cortisol rise at GH-releasing doses, and the dose-response data show these cannot be dialled out separately from GH (Massoud 1996). The 16-week study reported no serious adverse events, and the GH response recovered after stopping (Rahim 1998).

Cardiovascular caution cuts both ways. Hexarelin increased coronary perfusion pressure in perfused hearts through CD36 (Bodart 2002) and raised ejection fraction acutely in patients. Those are effects on a diseased organ produced by an unapproved compound with no outcome data. Anyone with cardiac disease belongs under the care of a cardiologist, not a protocol.

Predictable from GH physiology. Fluid retention, paraesthesia, arthralgia, reduced insulin sensitivity. Glucose and HbA1c need watching in anyone with prediabetes, diabetes or metabolic syndrome.

IGF-1 and malignancy. The chronic study did not raise IGF-1 significantly, which is informative in itself, but the class concern stands: higher circulating IGF-1 associates with prostate and premenopausal breast cancer risk in epidemiology (Renehan 2004). Active malignancy should be treated as a contraindication.

Unknowns. No studied use beyond 16 weeks. No pregnancy, lactation or paediatric data outside small research settings. No interaction studies with insulin, glucocorticoids or GLP-1 agonists.

Product quality. Hexarelin is not an approved pharmaceutical anywhere, so every available product is research-grade or grey-market. Analytical surveys of seized peptide products repeatedly find wrong identity, wrong quantity and degradation products (Weber 2017). See peptide sourcing.

Legal and regulatory status

United States. No approved hexarelin product and no approved indication. Hexarelin does not appear in category 1 or category 2 of FDA’s 503A bulk drug substance list (updated 14 May 2026), and it is not in the separate table of substances FDA flags as presenting significant safety risks. Absence from those lists is not permission: a bulk substance may be used in 503A compounding only if it meets one of the statutory conditions, and an unapproved, unlisted peptide does not. See the FDA 2026 compounding update and are peptides legal.

European Union and Germany. No EMA or BfArM authorisation. Hexarelin is named explicitly in the annex to Germany’s Anti-Doping Act (AntiDopG) among the growth hormone releasing peptides. Under § 2(3), acquiring, possessing or importing more than a “non-small quantity” for the purpose of doping in sport is an offence, and the quantity regulation (DmMV, in force 16 March 2023) puts that threshold at 1.5 mg for the GHRP group, hexarelin included by name.

Sport. Prohibited at all times under section S2 of the WADA list, by class. Urinary metabolites of hexarelin have been characterised for anti-doping purposes alongside GHRP-1, GHRP-2, GHRP-6 and ipamorelin, so detection is established. See peptides and anti-doping rules.

How hexarelin fits

Hexarelin is the clearest illustration of why I treat GH secretagogues as pharmacology rather than therapy. It is the strongest GH releaser available, it was studied properly for four months, and the body-composition endpoints did not move. If someone wants a GH secretagogue with the least hormonal noise, ipamorelin is the better choice. If the target is visceral fat with phase 3 evidence, that is tesamorelin. If the target is the heart, the honest answer is that the CD36 line of research deserved a real trial and never got one.

Related Articles

• GHRP-2 (Pralmorelin): Potent GH Release, Thin Outcome Data — the comparator with a diagnostic approval.
• GHRP-6: The Original GH-Releasing Peptide — the parent compound hexarelin was derived from.
• Ipamorelin: A Physician’s Guide — the selective alternative.
• Tesamorelin: Visceral Fat, Liver Fat and the GHRH Analogue With Trials — what trial-grade evidence in this axis looks like.
• Peptide Therapy for Athletes: What’s Banned Under WADA Rules in 2026 — class-based prohibition and detection.