Hexarelin

Hexarelin (also called examorelin or HEX) is a synthetic hexapeptide with the sequence His-D-2-methyl-Trp-Ala-Trp-D-Phe-Lys-NH₂. It is structurally derived from GHRP-6 with a methyl modification at the tryptophan in position 2. The compound activates the ghrelin receptor (GHSR1a) on pituitary somatotrophs to trigger GH release, with potency comparable to GHRP-2. It also has documented effects on cardiac tissue that may be mediated through a separate cardiac binding site distinct from GHSR1a. Hexarelin was developed by Mediolanum Farmaceutici in Italy in the 1990s and progressed through Phase 2 cardiovascular development before being discontinued.

The molecule was developed as a structural refinement of GHRP-6 with improved metabolic stability and stronger biological effects. The methyl modification at position 2 reduces susceptibility to enzymatic degradation and produces a longer functional half-life than GHRP-6.

The cardiovascular development program led by Mediolanum Farmaceutici (and its US partner Smith Kline Beecham, later GlaxoSmithKline) tested hexarelin in cardiovascular indications through Phase 2. The program was discontinued in 2005 as part of a broader portfolio review at the sponsor. The cardiovascular dataset, while incomplete by Phase 3 standards, is the most substantial preclinical and Phase 1/2 cardiovascular file for any GHRP.

The Cardiovascular Evidence

The cardiovascular research on hexarelin is the most distinctive part of its evidence base.

Animal models of ischemia-reperfusion. Multiple studies have documented hexarelin protection against experimental myocardial infarction. The mechanisms include preserved mitochondrial function, reduced oxidative stress in cardiac myocytes, and reduced apoptosis in the periinfarct zone. Treatment given before or shortly after experimental ischemia produces measurable reductions in infarct size and improvements in functional recovery.

Heart failure animal models. Hexarelin administration in animal models of heart failure has improved cardiac contractility and reduced markers of cardiac stress. The mechanism appears to involve both direct cardiac effects and the broader anabolic effects of GH release.

Phase 1 and 2 cardiovascular trials. The Mediolanum/SKB Phase 2 program tested hexarelin in cardiovascular patient populations. The trial data, while not as extensive as a typical Phase 3 program, supported continued development before the commercial discontinuation in 2005. Detailed efficacy results from these trials were not extensively published after the program ended.

Long-term GH therapy studies. Rahim et al. (1998) in JCEM examined GH status during long-term hexarelin therapy. The study documented that the GH-releasing effect attenuates with chronic dosing, with desensitization developing over weeks to months. This is the typical pattern for ghrelin receptor agonists with continuous high-dose exposure.

The cardiovascular research distinguishes hexarelin from the rest of the GHRP class. The other older GHRPs (GHRP-2, GHRP-6) have not been pursued for cardiovascular indications at the same level. The discontinuation of the hexarelin cardiovascular program in 2005 represents one of the larger lost opportunities in the GHRP class, since the preclinical cardiac data was promising.

Hexarelin acts on both pituitary (for GH release) and cardiac tissue (for the cytoprotective effects). The two mechanisms appear partially independent.

Pituitary GH release. Hexarelin binds GHSR1a on pituitary somatotrophs and triggers a GH pulse with the standard cAMP/calcium cascade. GH-releasing potency is comparable to GHRP-2 and substantially higher than GHRP-6. The GH pulse peaks 15 to 30 minutes after subcutaneous injection.

HPA axis activation. Like GHRP-2 and GHRP-6, hexarelin produces cortisol and ACTH increase through central mechanisms. The Ghigo et al. 1997 study in JCEM documented hexarelin's ACTH and cortisol-releasing effects in normal subjects and Cushing's syndrome patients. The HPA effect is mediated through arginine vasopressin (AVP) pathways in the hypothalamus.

Cardiac binding site. This is the distinguishing feature of hexarelin. Animal studies have documented binding of hexarelin to cardiac tissue at concentrations and locations that suggest a separate receptor or binding site from GHSR1a. Whether this represents a distinct receptor (different from the ghrelin receptor) or a tissue-specific GHSR1a variant is incompletely characterized.

Cytoprotective effects. Hexarelin protects cardiac myocytes from ischemia-reperfusion injury in animal models. The protection involves reduced cell death, preserved cardiac function, and improved recovery after experimental infarction. The effects appear independent of GH release, since they occur in animals where GH signaling is blocked.

Anti-apoptotic effects. Beyond the cardiac protection, hexarelin has documented anti-apoptotic effects on other cell types in animal models, including skeletal muscle and certain neuronal populations.

The pharmacokinetic profile resembles GHRP-2. Subcutaneous administration produces peak plasma levels within 30 to 60 minutes with a half-life of approximately 70 minutes.

Regulatory status

No FDA approval, no EMA approval, no marketing authorization in any country. The Mediolanum cardiovascular program reached Phase 2 but was discontinued before registrational Phase 3 trials.

Hexarelin was added to the FDA Category 2 bulks list under Section 503A in September 2023, prohibiting compounding pharmacy preparation. The compound is one of those scheduled for reconsideration at the PCAC meeting on July 23 and 24, 2026. Without an approved indication and without a complete Phase 3 program, Category 1 reclassification is unlikely.

Hexarelin is on the WADA Prohibited List under section S2 (Peptide Hormones, Growth Factors, Related Substances, and Mimetics). Use in competitive sport is a doping violation in-competition and out-of-competition.

The compound continues to be sold by online research-chemical vendors as "for laboratory use only," with the standard quality control variability that applies to research-chemical peptides.

Dosing protocols and literature-reported ranges are documented in the approved label or trial publications referenced above.

The safety profile of hexarelin is well characterized through Phase 1 and Phase 2 trials. The most consistent findings:

Cortisol and ACTH increase. Similar to GHRP-2 and GHRP-6. Sustained cortisol increase with chronic dosing is a concern.

Prolactin increase. Modest, similar to other GHRPs.

Mild appetite stimulation. Less than GHRP-6 but more than ipamorelin.

Tachyphylaxis (receptor desensitization). Documented with chronic dosing. The GH-releasing effect attenuates over weeks of continuous high-dose administration, requiring cycling protocols to maintain responsiveness.

Injection-site reactions. Common with subcutaneous administration. Generally mild and self-limited.

Mild glucose increase. GH-induced insulin resistance is a class effect.

No serious cardiovascular adverse events have been documented in the Phase 1/2 trial dataset, despite the cardiac binding site. This is consistent with the cytoprotective rather than stimulatory profile.

The desensitization pattern is more pronounced for hexarelin than for some other GHRPs, which limits chronic dosing strategies. The combination with GHRH analogs (sermorelin, CJC-1295) is sometimes used to overcome this limitation through engagement of both receptor systems.

The GHRP family includes several compounds with overlapping but distinct profiles.

Hexarelin vs GHRP-2. Comparable GH-releasing potency. Comparable cortisol/ACTH/prolactin effects. Hexarelin has the cardiovascular research base; GHRP-2 has the Japanese diagnostic approval. The two are often considered roughly interchangeable for adult anabolic use.

Hexarelin vs GHRP-6. Hexarelin has higher GH-releasing potency and less appetite stimulation. The two share the same cortisol/ACTH profile.

Hexarelin vs Ipamorelin. Ipamorelin retains GH potency while minimizing cortisol, ACTH, prolactin, and appetite effects. Hexarelin has the cardiovascular research base that ipamorelin lacks but the off-target endocrine effects that ipamorelin avoids.

Hexarelin vs MK-677. MK-677 is the oral non-peptide ghrelin receptor agonist with daily 24-hour GH/IGF-1 increase. Hexarelin requires multiple daily injections for comparable effect. MK-677 has a larger Phase 2 evidence base for chronic dosing.

Hexarelin vs Tesamorelin/CJC-1295. GHRH analogs work on a different receptor system. Combining hexarelin with a GHRH analog produces synergistic GH release. Tesamorelin has the FDA approval (for HIV-associated lipodystrophy) that no GHRP has achieved.

For practical adult use, hexarelin's distinguishing feature is the cardiovascular research base. For users with cardiac concerns who want GHRP-class GH support, hexarelin has theoretical appeal based on the preclinical cardiac data. For users without cardiac considerations, ipamorelin's selectivity advantage typically makes it the more rational choice.