Hexarelin

Hexarelin (EP-23905) is a synthetic growth hormone releasing peptide and the most potent member of the GHRP class. It is a hexapeptide with the sequence His-D-2-methyl-Trp-Ala-Trp-D-Phe-Lys-NH2, developed in the early 1990s as a more potent alternative to GHRP-6. It acts as a ghrelin receptor (GHS-R1a) agonist at the hypothalamus and pituitary, driving endogenous growth hormone secretion rather than supplying exogenous hormone.

On a dose-for-dose basis hexarelin produces the strongest growth hormone release of any available GHRP, exceeding GHRP-2, GHRP-6 and ipamorelin. In human work the growth hormone response to hexarelin was significantly higher than the response to GHRH alone (Arvat et al., 1997). The trade-off is selectivity. Where ipamorelin binds with high specificity for growth hormone release, hexarelin activates more broadly, producing modest increases in ACTH, cortisol and prolactin, with ACTH and cortisol-releasing activity comparable to human corticotropin-releasing hormone (hCRH).

Hexarelin also desensitises the ghrelin receptor faster than other compounds in the class, making cycling mandatory rather than optional. This positions it as a purpose-built short-cycle tool rather than a long-term secretagogue.

What separates hexarelin from the rest of the class is a distinct cardiac binding site. Bodart et al. (1999) identified an 84,000 dalton receptor in rat cardiac membranes with a single class of high-affinity binding sites, which MK-0677 and EP51389 failed to displace, confirming it is separate from the pituitary ghrelin receptor. Bodart et al. (2002) identified that receptor as CD36, a multifunctional glycoprotein expressed in cardiomyocytes and microvascular endothelial cells, with the highest binding density in the ventricles, followed by atria, aorta, coronary arteries and carotid arteries.

Hexarelin holds no FDA approval for any indication. It has been evaluated in human trials for growth hormone release but not for therapeutic applications, and all cardiovascular data remains preclinical.

Hexarelin binds GHS-R1a in the hypothalamus and anterior pituitary. Receptor occupancy activates adenylyl cyclase, raising intracellular cyclic AMP and driving calcium-dependent exocytosis of growth hormone from pituitary somatotrophs. In parallel it suppresses somatostatin tone, removing the physiological brake on secretion. This dual action, stimulating release while blocking inhibition, accounts for the magnitude of the pulse.

The pharmacokinetics are short. Growth hormone returns to baseline within 90 minutes to 2 hours post-injection, and the half-life is approximately 30 to 45 minutes, which drives the 2 to 3 times daily dosing requirement.

Selectivity is the key differentiator. In human comparison work, both GHRP-2 and hexarelin caused modest increases in ACTH, cortisol and prolactin, with corticotropic activity similar to hCRH and prolactin stimulation present but weaker than TRH (Arvat et al., 1997). This broader receptor activation is the mechanistic basis for reported anxiety, irritability, sleep disruption and libido changes, and it is dose-dependent.

Downstream, released growth hormone acts on hepatic receptors to stimulate IGF-1 production, mediating muscle protein synthesis, lipolysis via hormone-sensitive lipase, cellular repair and tissue growth.

The cardiac mechanism is separate. Hexarelin binds CD36 in cardiomyocytes and microvascular endothelium. CD36 activation increased coronary perfusion pressure dose-dependently, and this response was absent in CD36-null mice, with the vasoconstrictive response correlating with CD36 expression (Bodart et al., 2002). Locatelli et al. (1999) showed that in hypophysectomised rats, which cannot mount a growth hormone response, hexarelin still prevented exacerbation of ischaemia-reperfusion damage, protected against rises in left ventricular end-diastolic pressure, reduced creatine kinase release, enhanced prostacyclin release and improved contractility recovery. Further animal work shows attenuation of atherosclerosis, reduced cardiac fibrosis and protection against abdominal aortic aneurysm formation. Mao et al. (2014) concluded hexarelin acts through both GHS-R and cardiac CD36 and may be promising for some cardiovascular conditions, pending human investigation.

Hexarelin drives large, rapid, pulsatile growth hormone release through GHS-R1a, with repeated daily pulses raising cumulative growth hormone and downstream IGF-1 exposure. The functional output is increased muscle protein synthesis, lipolysis through hormone-sensitive lipase activation, accelerated cellular repair and improved sleep architecture, with growth hormone naturally peaking in deep sleep and a pre-bed dose reinforcing that pulse.

Magnitude is the differentiator: the growth hormone response to hexarelin was significantly higher than to GHRH alone in humans, and Deghenghi et al. (1994) described it as a highly effective growth hormone releaser, slightly more effective than GHRP-6 in rats. Imbimbo et al. (1994) established dose-dependent, reproducible subcutaneous efficacy in a double-blind, placebo-controlled rising dose study.

Alongside this, hexarelin measurably activates the corticotropic axis and prolactin release. That is not a theoretical concern; it is documented in human data and is the mechanism behind the broader side effect profile.

The cardiac profile is unique in the class. Preclinical work shows protection from ischaemia-reperfusion injury, improved left ventricular function and contractility, reduced cardiac fibrosis and attenuated atherosclerosis, all mediated via CD36 and independent of growth hormone release. No human cardiovascular trial exists.

Efficacy is time-limited. Rahim and Shalet (1998) measured mean growth hormone areas under the curve of 19.1, 13.1, 12.3 and 10.5 micrograms per litre per hour at weeks 0, 1, 4 and 16 in 12 healthy elderly subjects on twice-daily therapy, a decline of roughly 45%. Four weeks after discontinuation the response returned to 19.4 micrograms per litre per hour, not significantly different from baseline. That same study found no significant change in serum IGF-1, IGFBP-3, total body fat, lean body mass or bone mineral density across 20 weeks, a relevant caveat when projecting body composition outcomes.

Weeks 1 to 2 are dominated by sleep quality improvement, with acute post-injection flushing, transient hand tingling, appetite increase and mild water retention commonly reported. Subtle mood shifts, mild anxiety or irritability may appear in this window, consistent with modest ACTH, cortisol and prolactin elevation; marked symptoms indicate the dose is too high.

Weeks 2 to 4 bring the clearest recovery signal: reduced inter-session soreness and improved training tolerance. Body composition change begins but remains subtle.

Weeks 4 to 8 represent the practical efficacy window. Fat loss and muscle fullness become visible while desensitisation is already underway; the growth hormone area under the curve at week 4 was significantly below baseline in the 16 week desensitisation study.

Beyond 8 weeks the decline is meaningful. At week 16 the response was approximately 45% below baseline. Four weeks off restored it to a value not significantly different from baseline, which is precisely why the 4 to 8 weeks on, 4 weeks off structure exists.

Subjectively, users consistently report stronger effects than from ipamorelin or sermorelin, including a more pronounced post-injection flush, stronger sleep improvement and faster recovery. This aligns with the pharmacology. In practice, most experienced users position hexarelin as a short-term tool for a defined goal, an aggressive cut, injury recovery or a short bulk, and revert to CJC-1295 with ipamorelin for ongoing use, which covers both the GHRH and ghrelin pathways with less desensitisation and a cleaner profile. Some alternate hexarelin cycles with ipamorelin maintenance phases during the off weeks.

Note the ceiling on expectations: the elderly cohort study found no significant change in IGF-1, IGFBP-3, total body fat, lean body mass or bone mineral density over 20 weeks at 1.5 mcg/kg twice daily.

Published human dosing is limited. The rising dose study used escalating subcutaneous doses; the desensitisation study used 1.5 mcg/kg twice daily for 16 weeks, approximately 137 mcg per injection for a 91 kg subject. The protocols below reflect clinical practice patterns rather than formal dose-finding data.

Standard practice is 100 to 200 mcg per injection, 2 to 3 times daily, morning and pre-bed, both fasted, run 4 to 8 weeks on with 4 weeks off. A conservative ramp is 100 mcg twice daily for weeks 1 to 2, 150 mcg twice daily for weeks 3 to 4, and 200 mcg twice daily for weeks 5 to 8, moving to three times daily only if tolerated, followed by 4 to 6 weeks off.

Body weight tiering: under 150 lbs, 100 mcg per injection; 150 to 200 lbs, 100 to 150 mcg; over 200 lbs, 150 to 200 mcg.

Reconstitution: 5 mg vial with 2 mL bacteriostatic water yields 250 mcg per 10 units on an insulin syringe.

Fasting is not optional for efficacy. Dose at least 2 hours after food and 30 minutes before eating; carbohydrate-driven insulin elevation blunts the growth hormone response. Glucocorticoids may also blunt it.

Cycling is mandatory given the desensitisation kinetics: progressive decline from week 1, roughly 45% reduction by week 16, full recovery after 4 weeks off.

Stacking note: with CJC-1295 no DAC, both compounds are run at 100 to 200 mcg subcutaneously, dosed together and fasted, for 4 to 8 weeks then 4 weeks off. Do not combine hexarelin with ipamorelin, GHRP-2, GHRP-6 or MK-677; stacking multiple ghrelin agonists is redundant and compounds side effects. Do not combine multiple GHRH analogues.

Monitoring: baseline IGF-1 with a retest at 4 to 8 weeks, fasting glucose if there is any insulin resistance history, and prolactin testing if libido changes persist.

Imbimbo et al. (1994), a double-blind placebo-controlled rising-dose study in the European Journal of Clinical Pharmacology, established dose-dependent, reproducible GH release from subcutaneous hexarelin in humans with good tolerability. Deghenghi et al. (1994) demonstrated long-lasting GH release in infant and adult rats, slightly exceeding GHRP-6.

Arvat et al. (1997) compared hexarelin and GHRP-2 against GHRH, TRH and hCRH. Both secretagogues produced GH release significantly above GHRH alone and both caused modest ACTH, cortisol and prolactin rises; corticotroph activity was similar to hCRH, prolactin stimulation weaker than TRH. This is the mechanistic basis for hexarelin's non-selectivity.

Rahim and Shalet (1998) quantified desensitisation over 16 weeks of twice-daily therapy in 12 healthy elderly subjects. Mean GH areas under the curve were 19.1, 13.1, 12.3 and 10.5 mcg/L/h at weeks 0, 1, 4 and 16, returning to 19.4 mcg/L/h four weeks after discontinuation, not significantly different from baseline. IGF-1, IGFBP-3, total body fat, lean body mass and bone mineral density were unchanged across the 20-week period. Desensitisation is therefore progressive, partial and fully reversible, and this time course defines cycling practice for ghrelin agonists generally.

The cardiac literature is preclinical. Bodart et al. (1999) identified an 84,000 dalton cardiac binding site not displaced by MK-0677 or EP51389, distinct from pituitary GHS-R1a. Bodart et al. (2002) identified it as CD36; the coronary perfusion pressure response was absent in CD36-null mice. Locatelli et al. (1999) showed hexarelin limited ischaemia-reperfusion injury in hypophysectomised rats, preventing left ventricular end-diastolic pressure rises, reducing creatine kinase release and enhancing prostacyclin release, confirming GH-independent cardioprotection. Mao et al. (2014) reviewed both GHS-R and CD36 pathways and concluded hexarelin may be promising for some cardiovascular conditions pending human investigation.