ACE-031 vs Hexarelin

Soluble decoy receptor for ActRIIB; sequesters myostatin, activin, and GDF-11 to remove multiple brakes on muscle and bone growth simultaneously

ACE-031 is a soluble decoy receptor fusion protein consisting of the extracellular domain of activin type IIA receptor (ActRIIA) linked to a human IgG1 Fc region, developed by Acceleron Pharma to bind and sequester myostatin, activin, and related TGF-beta superfamily ligands that negatively regulate muscle mass, with the goal of promoting muscle growth in severe wasting conditions including Duchenne muscular dystrophy. By competitively binding circulating myostatin and related ligands, ACE-031 reduces signaling through the Smad2/3 pathway that suppresses muscle satellite cell activation and protein synthesis; in preclinical models of myopathy, blockade of ActRIIA signaling produced significant increases in lean mass, supporting its evaluation in Phase 2 human trials. A Phase 2 randomized placebo-controlled trial in ambulatory boys with Duchenne muscular dystrophy demonstrated significant increases in lean body mass; however, the trial was halted early due to vascular-related adverse events including epistaxis and telangiectasias, attributed to off-target inhibition of angiogenic TGF-beta family ligands, and the Acceleron clinical program was subsequently discontinued. ACE-031 has no FDA approval and is not approved for any indication; commercial development was halted due to the adverse event signal identified in the clinical trial; it is not commercially available, and the vascular safety concern inherent to pan-ActRIIA ligand inhibition represents an unresolved risk that precludes its extrapolation to general performance or muscle enhancement applications.

Potent synthetic GHRP; strongest GH secretagogue in its class; also activates CD36 scavenger receptor for cardioprotective effects

Hexarelin is a synthetic hexapeptide GH secretagogue that acts as an agonist at the ghrelin receptor (GHS-R1a) and is among the most potent GHRP-class peptides characterized in human studies, producing robust GH release at low doses via a mechanism that synergizes with endogenous GHRH and partially suppresses somatostatin. In addition to its pituitary GHS-R1a effects, hexarelin has been shown to engage CD36 receptor-mediated pathways in cardiac tissue, suggesting biological activity beyond GH secretion, though the cardiac pharmacology has not been developed into an approved clinical application. Human endocrine studies have directly compared hexarelin-induced GH release with ghrelin and GHRH in healthy volunteers, confirming its potent pituitary activity; repeated administration produces progressive attenuation of the GH response consistent with receptor desensitization. Hexarelin is not FDA-approved for any indication; it is used as a research tool for characterizing the GH secretagogue receptor system and has not been evaluated for safety or efficacy in performance enhancement contexts. Research interest in hexarelin centers on two distinct biological roles: its potent GH-secreting activity — relevant to muscle recovery and body composition research contexts — and its cardiac tissue effects via CD36 receptor pathways, which distinguish it mechanistically from simpler GHRPs such as GHRP-2 and GHRP-6. Hexarelin dosage in research contexts: published human studies have used intravenous doses of 1–2 mcg/kg to characterize GH secretion kinetics. In clinical research protocols, subcutaneous doses of 100–200 mcg per injection are most commonly cited, typically administered once or twice daily. Hexarelin's potency relative to other GHRPs means lower doses are required for equivalent GH stimulation; however, receptor desensitization with repeated dosing is more pronounced than with selective peptides such as ipamorelin, which has driven research interest in cycling protocols and combination approaches. Administration is by subcutaneous injection. Hexarelin vs ipamorelin: the two peptides differ substantially in selectivity and desensitization profile. Hexarelin is a non-selective GHRP that stimulates GH alongside modest elevations in cortisol, prolactin, and ACTH — effects documented in human challenge studies. Ipamorelin, by contrast, is one of the most selective GHRPs characterized, producing GH secretion with minimal cortisol or prolactin co-stimulation. For research focused specifically on GH secretion with a cleaner hormonal background, ipamorelin is generally preferred; hexarelin is studied in contexts where its dual CD36/GHS-R1a pharmacology is the research focus. Providers offering hexarelin are listed in the PeptideBase directory.