Research digest // body composition
Ipamorelin releases growth hormone with no measurable cortisol cost — here is what the body-composition literature has actually recorded.
A scholarly digest of the lean-mass, fat, and IGF-1 findings, the pharmacokinetics, and the one human efficacy trial that missed its endpoint. Every number is cited.
The short version
Ipamorelin is a small synthetic peptide — five amino acids long — that tells the pituitary gland (the body's master hormone gland) to release a pulse of growth hormone. Its claim to fame is being clean about it: it raises growth hormone without raising the stress hormone cortisol, unlike the older peptides in its family [1]. People are most interested in it for body composition — the balance of muscle to fat. The honest state of the evidence: in animals it nudges lean tissue and bone, and it can change fat and appetite in ways that are not purely growth-hormone driven [4][7]. In rats, growth happened without a measurable rise in IGF-1, the protein that usually carries growth hormone's signal [4]. The single human efficacy trial — for slow bowel recovery after surgery — did not beat placebo [3]. Ipamorelin is not approved as a drug anywhere. What people report, including the downsides, is on the effects page.
What ipamorelin is, in one paragraph
Ipamorelin (sequence Aib-His-D-2-Nal-D-Phe-Lys-NH2; also coded NNC 26-0161) is a synthetic pentapeptide that selectively activates the ghrelin / growth hormone secretagogue receptor (GHS-R1a — the same receptor the hunger hormone ghrelin uses) on the pituitary's growth-hormone cells [1]. When Raun and colleagues first characterized it in 1998, it released growth hormone as potently as the older peptide GHRP-6 (swine ED50 of 2.3 nmol/kg versus 3.9 nmol/kg for GHRP-6) yet did not raise ACTH or cortisol even at doses more than 200-fold above its growth-hormone ED50 [1]. That selectivity — growth hormone up, cortisol and prolactin flat — is the single feature that defines the molecule and separates it from every growth-hormone-releasing peptide that came before it.
The body-composition signal: lean mass, bone, fat
The body-composition story is more interesting than a simple "growth hormone builds muscle" headline, and the studies say so. In adult female Sprague-Dawley rats, subcutaneous ipamorelin at 18, 90, and 450 μg/day (divided three times daily for 15 days) raised the longitudinal bone-growth rate from 42 μm/day on vehicle to 44, 50, and 52 μm/day in a clean dose-response — and it did so with no change in total IGF-1, IGF-binding proteins, or bone-turnover markers [4]. That last detail matters: it means part of the skeletal effect is driven by the local growth-hormone pulse, not by the systemic IGF-1 axis people usually assume is doing the work. On the fat side, two weeks of twice-daily subcutaneous ipamorelin produced a roughly 15% body-weight increase in both growth-hormone-deficient and growth-hormone-intact mice, with elevated fat-pad weights and serum leptin in both genotypes [7] — direct evidence that some of ipamorelin's effect on adiposity is growth-hormone-independent. The body-composition picture, then, is genuinely mixed: a lean, bone-favoring signal alongside a class-level appetite-and-fat signal, and which dominates depends on the model. The full breakdown sits on the Ipamorelin research page.
What the human data does and does not show
Human evidence on ipamorelin is thin and, where it exists, sobering. The only published Phase 2 randomized controlled trial (NCT00672074) gave 0.03 mg/kg intravenously twice daily for up to seven days to 114 adults recovering from bowel resection, testing whether it would speed the return of normal bowel function. It missed its primary endpoint: median time to first tolerated meal was 25.3 hours with ipamorelin versus 32.6 hours with placebo (p = 0.15) [3]. No ipamorelin-specific safety signal emerged in that short window — treatment-emergent adverse events occurred in 87.5% of the ipamorelin arm versus 94.8% of placebo — but efficacy was not demonstrated [3]. Separately, a human pharmacokinetic study (n = 8 per dose level) characterized a terminal half-life of about 2 hours and a single growth-hormone pulse peaking roughly 40 minutes after dosing [2]. That is the entire controlled human record. Everything else is animal data, mechanism, and community report.
Approval status, stated plainly
Ipamorelin is not FDA-approved for any indication, and it never has been [3]. It was developed by Novo Nordisk in the 1990s, advanced only as far as the Phase 2 ileus program described above, and was never marketed as a drug. In 2024 the FDA removed ipamorelin acetate from Category 2 of the interim Section 503A bulk-substances list and reviewed it at the October 29, 2024 Pharmacy Compounding Advisory Committee meeting, tightening compounding-pharmacy access. It is also prohibited in sport at all times under the World Anti-Doping Agency list (category S2). This site is an editorial digest of that published record — it documents the research, it does not sell the compound and it gives no dosing guidance. Reported effects and the cautions worth knowing are on the Ipamorelin effects page.