History

Hexarelin was developed by Mediolanum Farmaceutici (Italy), with chemistry by Romano Deghenghi (Europeptides, France), as a more stable, orally active derivative of GHRP-6 (a 2-methyl-tryptophan substitution). First human dose-response studies appeared in the early 1990s, and academic interest peaked in the mid-to-late 1990s around GH-deficiency diagnostics, receptor desensitization, and cardiac effects. Hexarelin itself never progressed past Phase II and was never marketed. An oral analog, EP-1572/ARD-07, later became macimorelin and was FDA-approved as Macrilen in 2017 — but that was a different molecule. Exact early dates are approximate.

Hexarelin is a synthetic peptide that mimics the hunger hormone ghrelin to provoke a sharp, short-lived burst of growth hormone (GH). Small human studies in the 1990s showed it does this reliably, but every trial was tiny, brief, and measured surrogate markers rather than real-world outcomes. It was never approved anywhere, and it is banned in sport.

What it is

Hexarelin is a synthetic hexapeptide — six amino acids, sequence H-His-D-2-methyl-Trp-Ala-Trp-D-Phe-Lys-NH2 — with the molecular formula C47H58N12O6, a mass of about 887 g/mol, and CAS number 140703-51-1. It was created by modifying the older peptide GHRP-6, replacing a tryptophan residue with 2-methyl-tryptophan to make it more stable against enzymes and orally active.

Its main job is to act as an agonist at the growth-hormone-secretagogue receptor (GHS-R1a) — the same receptor the natural hormone ghrelin uses — in the hypothalamus and pituitary. Activating that receptor drives a pulse of GH release, even though hexarelin shares no sequence with ghrelin itself. At higher doses it also modestly stimulates ACTH, cortisol, and prolactin. Separately, hexarelin binds a receptor called CD36 in heart muscle, which researchers proposed as the route for cardiac effects that appear independent of GH. Its plasma half-life is roughly 55 minutes.

The claims

In the research literature, hexarelin was studied legitimately for two things: diagnosing and treating GH deficiency (in both children and adults), and protecting or supporting the heart after a heart attack or in heart failure.

In the gray market, it is sold for very different reasons — muscle growth, fat loss, faster recovery, anti-aging, and better sleep or skin. Those claims extrapolate from the fact that hexarelin acutely spikes GH and from rodent experiments. None of them has been tested in a controlled human trial measuring those specific outcomes.

The evidence

The human evidence is real but early, small, and built almost entirely on surrogate endpoints (hormone levels and heart-imaging numbers) rather than clinical outcomes like growth, body composition, or survival.

In a 1994 double-blind, placebo-controlled study (Imbimbo et al.), 12 healthy men received intravenous hexarelin. GH rose dose-dependently, peaking around 55 ng/mL at the top dose versus about 3.9 on placebo, peaking near 30 minutes. A 1996 dose-response study (Massoud, Hindmarsh & Brook) confirmed potent GH release but also showed that prolactin and cortisol climb at higher doses, while staying nearly unchanged at low doses.

On the cardiac side, a 2001 study (Broglio et al.) gave acute intravenous hexarelin to small groups — 7 healthy people, 7 with severe GH deficiency, and patients with cardiomyopathy. It increased left-ventricular ejection fraction in the normal and GH-deficient subjects through a positive effect on the heart muscle that appeared independent of GH. These were tiny, one-time exposures measuring an imaging number, not patient outcomes.

A key limitation surfaced in longer dosing. In a 16-week study (Rahim, O’Neill & Shalet, 1998), the GH response roughly halved over time — partial, reversible desensitization that recovered after stopping. A companion 1999 paper found chronic dosing did not over-stimulate the adrenal axis or prolactin. Laboratory work backs up the desensitization story: in cells expressing the human receptor, the calcium response blunted within just 2 to 5 minutes of a first dose (Orkin et al., 2003), and receptor regulation varied by age in rats (Bresciani et al., 2004).

The largest body of work is animal cardiac research, all in rodents — improved heart function after experimental heart attack and GH-independent cardioprotection in rats and mice. That is suggestive, not proof in humans.

The skeptical read: there is no Phase III, no replicated randomized controlled trial, and no hard clinical-outcome data. The human cardiac signal is acute and tiny. Much of the early human and discovery work involved the developer’s own scientists — normal for early pharma, but worth noting. And the rapid, reversible desensitization is a genuine pharmacological problem that helped sink development. The popular muscle and anti-aging claims, specifically, have no controlled human trials behind them at all.

Safety and side effects

In short, low-dose controlled studies, hexarelin was generally well tolerated. Reported acute effects include transient flushing or warmth and mild hunger — both consistent with activating the ghrelin receptor.

The clearest dose-related issue is off-target hormone stimulation: prolactin and cortisol/ACTH rise at higher doses, while low doses leave them largely alone. The 16-week study did not show over-activation of the adrenal axis or prolactin. The more practical limitation is tachyphylaxis — the GH response fades with repeated use (blunting within minutes in cells, GH output roughly halved by 16 weeks in people) before recovering after a washout. That limits sustained usefulness more than it signals toxicity.

The honest caveats: there is no long-term human safety data, and theoretical class concerns — such as effects on blood sugar and insulin from stimulating the GH axis — are not well characterized for hexarelin specifically in humans. On top of that, anything sold as a “research chemical” is unregulated; identity, purity, potency, and sterility are all unverified, which is a separate hazard. Nothing here is medical advice.

Legal and regulatory status

Hexarelin itself was never approved for any use by the FDA, the EMA, or any other regulator. It reached only Phase II for GH deficiency and heart failure before development was abandoned, and it was never marketed.

A common confusion is worth clearing up. A May 14, 2007 FDA orphan-drug designation often attributed to “hexarelin” was actually granted to a different compound — ARD-07 / EP-1572, an oral GH secretagogue (Ardana Bioscience, licensed from Aeterna Zentaris) for diagnosing adult GH deficiency. An orphan designation is not a marketing approval. And contrary to the idea that this program simply lapsed, the same molecule resurfaced as macimorelin (AEZS-130) and was FDA-approved on December 20, 2017 as Macrilen for diagnosing adult GH deficiency. So an oral analog of hexarelin did eventually reach market — but hexarelin itself never did.

In sport, the World Anti-Doping Agency prohibits hexarelin at all times under class S2.2.4 (GH-releasing peptides). The 2026 Prohibited List names “examorelin (hexarelin)” explicitly, alongside related GHRPs. Because it has no approved medical use, there is no realistic basis for a therapeutic use exemption.

In practice it is sold online as a “research chemical / not for human consumption,” a label that carries no obligation to prove what is actually in the vial.

Bottom line

Hexarelin reliably triggers a short GH pulse in humans, and small acute studies hint at a direct heart-muscle effect. But every human study is tiny, brief, and built on surrogate markers; a rapid, reversible loss of response helped end its development; it was never approved anywhere; and it is banned at all times in sport. The popular muscle and anti-aging claims have no controlled human evidence behind them.

Evidence grade: Preliminary human.

Hexarelin: A Potent GH Trigger That Stalled at Early Human Trials