Hexarelin

Mechanism

Hexarelin is a synthetic hexapeptide (His-D-2-MeTrp-Ala-Trp-D-Phe-Lys-NH₂) classified as a growth hormone-releasing peptide (GHRP). Like ipamorelin and GHRP-6, it binds the ghrelin receptor (GHS-R1a) on anterior pituitary somatotrophs and stimulates endogenous GH secretion.

The distinguishing feature is non-selectivity:

• Strong GH-releasing effect acutely (larger pulse than ipamorelin at typical doses)
• Significant ACTH/cortisol elevation (clinically meaningful, not background noise)
• Significant prolactin elevation
• Some appetite stimulation (less than GHRP-6, more than ipamorelin)

There is also evidence for hexarelin binding CD36 receptors on cardiac myocytes — a non-ghrelin-receptor mechanism with unclear long-term implications. Some animal data suggests cardioprotective effects at modest doses; some human data has raised concerns about cardiac structural changes at high doses.

Half-life is approximately 70 minutes. Like other GHRPs, it requires multiple daily dosing to maintain pulsatile effect.

What the evidence shows

Pharmacology and acute effects (published human studies):

• Strong GH-releasing effect, dose-dependent up to about 2 mcg/kg
• Plateau in GH response above ~2 mcg/kg
• Cortisol elevation: typically 30–80% above baseline post-injection
• Prolactin elevation: typically 50–200% above baseline post-injection
• Both effects more pronounced in women than men

Tachyphylaxis (Rahim et al, Clin Endocrinol 1998):

A study of repeated daily hexarelin injection in healthy adults showed:

• Robust GH response on day 1
• Substantially reduced GH response by day 7 (~50% diminished)
• Further attenuation by day 16

The tachyphylaxis is real and well-documented. It is the reason hexarelin was abandoned as a candidate therapeutic for adult GH deficiency — chronic dosing didn’t sustain the effect.

Cardiac effects:

• Animal data shows mixed effects: cardioprotective in some ischemia-reperfusion models, structural concerns at high chronic doses
• Human data is sparse; Phase 2 work in cardiomyopathy was exploratory and did not advance
• The CD36 binding is mechanistically interesting but the long-term implications in metabolically normal users are uncharacterized

For the body-composition / muscle indications it’s marketed for:

No published RCT evidence. Gray-market enthusiasm relies on the acute GH spike, which the published data shows is not sustained over weeks of daily dosing.

Dosing literature

There is no approved dose. Gray-market protocols use:

• Subcutaneous: 100–300 mcg per dose
• Frequency: 1–3 times daily, often pre-sleep
• Cycle structure: Some protocols cycle 4 weeks on / 2 weeks off to limit tachyphylaxis

The cycling protocols implicitly acknowledge the tachyphylaxis problem. They don’t solve it — they manage it.

Risks and adverse events

Common in human studies:

• Cortisol elevation (clinically meaningful, not subclinical)
• Prolactin elevation (clinically meaningful — can produce galactorrhea in women, gynecomastia signal in men)
• Injection-site reactions
• Flushing, head rush
• Hunger
• Tingling / paresthesia

Less common:

• Lactation in male users (rare but reported, consistent with prolactin elevation)
• Insulin resistance with sustained use
• Tachyphylaxis-driven dose escalation creating a use pattern that compounds adverse effects

Theoretical / long-term concerns:

• Chronic cortisol elevation has well-known harms: muscle catabolism, fat accumulation (paradoxical to body-composition goals), insulin resistance, immune suppression, mood effects
• Chronic prolactin elevation has known harms: bone density loss with long enough exposure, sexual dysfunction, possible pituitary effects
• The CD36 cardiac binding is uncharacterized for chronic exposure
• Same IGF-1-axis cancer-promotion concerns as other GH-axis manipulations

Quality concerns:

The gray-market peptide channel sells hexarelin alongside ipamorelin and CJC-1295. The hexapeptide structure is short and synthesizable, but the mass-spec verification rates are no better than for the rest of the class.

Regulatory status

Where to get it

We do not route readers to a fulfillment partner for hexarelin under any circumstance. The combination of cortisol/prolactin concerns, tachyphylaxis that encourages dose escalation, and absence of efficacy evidence for the marketed indications puts it firmly in the Cautionary zone.

If your goal is GH-axis manipulation through a GHRP, the selective alternative (ipamorelin) is Investigational — not endorsed, but a meaningfully better profile than hexarelin’s.

(See How we make money.)

References (selected)

1. Rahim A, O’Neill PA, Shalet SM. The effect of repeated administration of hexarelin on growth hormone secretion in healthy adults. Clin Endocrinol 1998. PubMed
2. Imbimbo BP et al. Hexarelin, a synthetic growth hormone (GH) releasing peptide, is a potent stimulator of GH secretion in adults. Eur J Clin Pharmacol 1994.
3. Loche S et al. The growth hormone-releasing activity of hexarelin, a new synthetic hexapeptide, in short normal and obese children and in hypopituitary subjects. J Clin Endocrinol Metab 1995.
4. Bisi G et al. Acute cardiovascular and hormonal effects of GH and hexarelin, a synthetic GH-releasing peptide, in humans. J Endocrinol Invest 1999.
5. WADA Prohibited List — Section S2 — current revision.