Frequently Asked

Ipamorelin is a synthetic pentapeptide — five amino acids, with two of them non-natural (alpha-aminoisobutyric acid and D-2-naphthylalanine) — assembled and characterized at Novo Nordisk in 1998 under the laboratory code NNC 26-0161 ^[1]. It acts as a selective agonist at the growth hormone secretagogue receptor type 1a (GHS-R1a), the same receptor that the endogenous hormone ghrelin occupies. The defining feature in the 1998 characterization was that ipamorelin released growth hormone without measurably elevating adrenocorticotropic hormone or cortisol — even at doses 200 times its growth-hormone median effective dose ^[1]. The molecular formula is C38H49N9O5, the molecular weight is 711.87 daltons, and the CAS number is 170851-70-4.

GHS-R1a is a Gq/11-coupled G-protein-coupled receptor. When ipamorelin binds, it activates phospholipase C, which generates inositol trisphosphate and diacylglycerol ^[10]. Inositol trisphosphate releases calcium from intracellular endoplasmic-reticulum stores, and L-type voltage-gated calcium channels add an inward calcium current at the cell surface. The combined rise in cytosolic calcium drives growth hormone exocytosis from anterior-pituitary somatotrophs. This signaling pathway is mechanistically distinct from the cyclic-AMP-mediated pathway used by the growth hormone-releasing hormone receptor — which is the basis for the supra-additive growth hormone pulses seen when GHRH analogs and growth hormone-releasing peptides like ipamorelin are administered together ^[10]. GHS-R1a also has notable constitutive (ligand-independent) activity, which contributes to basal growth hormone pulsatility and modulates the magnitude of ipamorelin-evoked responses ^[9].

Approximately 2 hours. The Gobburu 1999 pharmacokinetic-pharmacodynamic study in healthy human male volunteers reported a terminal elimination half-life of approximately 2 hours after single intravenous bolus doses, with plasma clearance 0.078 L/h/kg and steady-state volume of distribution 0.22 L/kg ^[2]. Growth hormone — the pharmacodynamic endpoint — peaked at roughly 40 minutes post-dose and declined exponentially toward baseline over the subsequent two to three hours. That study remains the human reference set; no comparable subsequent human pharmacokinetic study has been published.

The 1998 Raun paper compared ipamorelin to the earlier growth hormone-releasing peptides — GHRP-6, GHRP-2, and hexarelin — and found that all four agonize GHS-R1a and release growth hormone, but only ipamorelin did so without elevating adrenocorticotropic hormone or cortisol at growth-hormone-releasing doses ^[1]. The selectivity is at the level of the downstream hormonal response, not at the receptor itself — all of these peptides bind the same receptor. The mechanistic explanation is not fully worked out in the published literature, but it is consistent with subtly different intracellular signaling or biased agonism at GHS-R1a, where ipamorelin's structural features (the alpha-aminoisobutyric acid at position 1 and D-2-naphthylalanine at position 3) channel the signal toward growth hormone release without recruiting the hypothalamic-pituitary-adrenal arm of the response that the older GHRPs elicit.

Yes, but sparingly. The Gobburu 1999 healthy-volunteer pharmacokinetic study ^[2] is the foundational human work. The only published Phase 2 efficacy trial is Beck and colleagues' 2014 paper in the International Journal of Colorectal Disease, which enrolled 114 adults undergoing bowel resection and tested intravenous ipamorelin (0.03 mg/kg twice daily for up to 7 days) for postoperative ileus ^[7]. The trial missed its primary endpoint (p = 0.15 for time to first tolerated solid meal), and Helsinn discontinued clinical development thereafter. As of 2026, no subsequent Phase 2 or Phase 3 trial in any indication has been published or registered as completed. The total human clinical record is one pharmacokinetic study and one terminated Phase 2 trial.

Ipamorelin is not approved by the United States Food and Drug Administration for any human indication. At the October 29, 2024 meeting of the Pharmacy Compounding Advisory Committee, the committee voted against adding ipamorelin (free base) and ipamorelin acetate to the 503A bulks list — the list of bulk drug substances that compounding pharmacies are permitted to use under section 503A of the Federal Food, Drug, and Cosmetic Act ^[13]. The committee cited concerns over identity and characterization data and inadequate safety information for chronic human exposure. Separately, effective September 27, 2024, ipamorelin acetate was removed from Category 2 of the interim 503A bulks list following withdrawal of its nomination ^[14]. The two actions together meaningfully constrain the lawful supply of compounded ipamorelin from United States pharmacies.

Yes. Ipamorelin appears on the World Anti-Doping Agency Prohibited List under category S2.2 (Peptide Hormones, Growth Factors, Related Substances and Mimetics) and is prohibited at all times in and out of competition in all WADA-code sports ^[15]. Validated urinary detection assays — based on liquid chromatography–high-resolution tandem mass spectrometry — exist and have been adopted by WADA-accredited laboratories, with detection windows extending from hours to days post-administration depending on dose and route ^[16].

Several dose ranges recur in the literature. In the anesthetized rat intravenous bolus model, the growth-hormone-release ED50 was 80 ± 42 nmol/kg ^[1]. In the conscious swine model from the same paper, the ED50 was 2.3 ± 0.03 nmol/kg intravenous ^[1]. For subcutaneous bone-formation studies in adult female rats, Johansen and colleagues used 0, 18, 90, and 450 micrograms per day divided three times daily over 15 days ^[3], while Svensson and colleagues used continuous subcutaneous infusion at 0.5 mg/kg/day via osmotic minipump for 12 weeks ^[4]. The 2012 rodent postoperative-ileus model used intravenous bolus doses of 0.014 and 0.14 micromol/kg ^[6]. These are research doses in research animals — they are not human dosing recommendations and should not be back-calculated into human doses.

Because the two compounds engage different receptors that converge on the same downstream signal. CJC-1295 is a long-acting growth hormone-releasing hormone analog and activates the growth hormone-releasing hormone receptor — a Gs-coupled G-protein-coupled receptor that signals through cyclic AMP. Ipamorelin activates GHS-R1a — a Gq/11-coupled receptor that signals through phospholipase C and calcium ^[10]. The two pathways are non-overlapping inside the somatotroph, and their combined activation produces a supra-additive growth hormone pulse rather than a simple summed response. The Teichman 2006 paper in the Journal of Clinical Endocrinology & Metabolism characterized the long-acting CJC-1295 pharmacokinetics in healthy human adults, finding sustained dose-dependent insulin-like-growth-factor-1 elevation lasting up to 28 days post-dose ^[17]. This long tonic exposure provides the pharmacological backdrop against which a short-acting growth hormone-releasing peptide like ipamorelin can produce a discrete pulse in research models. The pairing is a mechanism-of-action observation in the literature, not a dosing recommendation.

The Beck trial randomized 114 adults undergoing bowel resection to ipamorelin (0.03 mg/kg intravenous twice daily for up to 7 days or until discharge) or placebo ^[7]. The primary endpoint was time to first tolerated solid meal. Median time was 25.3 hours in the ipamorelin arm versus 32.6 hours in the placebo arm — a roughly seven-hour numerical favor for ipamorelin, but p = 0.15, which did not reach statistical significance. Adverse-event rates were 87.5% on ipamorelin and 94.8% on placebo, with no specific safety signal flagged. The trial was registered as NCT00672074 and conducted by the Ipamorelin 201 Study Group. Helsinn — the developer at the time — discontinued clinical development after the publication. No Phase 3 trial followed.

No. The claim that ipamorelin has 'no side effects' overstates the published record and conflates two different statements. The accurate statement, from the 1998 Raun characterization, is that ipamorelin releases growth hormone in rodent and swine studies without measurably elevating adrenocorticotropic hormone, cortisol, or prolactin — receptor-level selectivity within a single dose ^[1]. That is a pharmacological observation about a narrow set of acute endpoints in animals. It is not equivalent to a clean clinical safety profile in humans under chronic dosing. Chronic growth hormone secretagogue exposure raises theoretical concerns common to the wider growth hormone / insulin-like-growth-factor-1 axis literature — insulin resistance, impaired glucose tolerance, fluid retention, arthralgia, carpal tunnel syndrome, and theoretical concern about promoting growth of pre-existing neoplasms — none of which have been adequately characterized for ipamorelin in long-duration human studies. The Beck 2014 trial ran for at most 7 days ^[7]; no longer human exposure has been published.

Three reasons appear in the public record. First, the 2014 Phase 2 trial for postoperative ileus missed its primary endpoint, removing the most concrete clinical-development hypothesis ^[7]. Second, Helsinn — the company that had been carrying that program — discontinued clinical development after the trial. Third, the regulatory environment narrowed in 2024 when ipamorelin acetate was removed from Category 2 of the interim 503A bulks list and the Pharmacy Compounding Advisory Committee voted against inclusion on the final 503A list ^[13][14]. Translational interest in growth hormone secretagogues persists — the 2025 Journal of Cachexia, Sarcopenia and Muscle scoping review documents that interest ^[11] — but most of the contemporary clinical-trial activity has shifted to other ghrelin-receptor agonists (notably anamorelin, which has its own metabolism literature ^[16]) rather than to ipamorelin specifically.