IPAMORELIN:
FREQUENTLY ASKED.

Ipamorelin (NNC 26-0161; CAS 170851-70-4) is a synthetic pentapeptide that selectively binds and activates the growth hormone secretagogue receptor type 1a (GHS-R1a), also known as the ghrelin receptor. When ipamorelin binds GHS-R1a on pituitary somatotroph cells, it activates Gq/11 G-protein signaling, which triggers intracellular calcium release. That calcium signal drives a discrete pulse of growth hormone (GH) secretion from the pituitary gland. GH then stimulates hepatic IGF-1 production, which mediates downstream anabolic effects via mTOR and PI3K/Akt signaling. As a research compound, ipamorelin is used to study GHS-R1a pharmacology, pulsatile GH secretion, and GH-dependent downstream biology including bone formation, GI motility, and nitrogen balance.^[1][17]

Before ipamorelin's characterization in 1998 by Raun et al., GHRP-class compounds such as GHRP-2 and GHRP-6 stimulated GH release but also activated the corticotroph axis (raising ACTH and cortisol) and to a lesser degree the lactotroph axis (raising prolactin). Ipamorelin does not meaningfully elevate ACTH or cortisol even at doses 200-fold above its GH-releasing ED50 in rats, and does not activate prolactin or TSH secretion.^[1] That selectivity profile — GH release without significant co-stimulation of other pituitary hormone axes — was unprecedented in the GHRP class. The Raun 1998 paper concluded that ipamorelin's selectivity for GH release was comparable to that of GHRH, which had previously been the benchmark for selectivity. A 2020 review of GHS pharmacological history designated ipamorelin the "prototypical selective GHS."^[17]

Three primary rodent studies examined skeletal effects. Subcutaneous ipamorelin at 18–450 mcg/day for 15 days in adult female rats produced a dose-dependent increase in longitudinal bone growth rate from 42 to 52 mcm/day, without changes in circulating IGF-1.^[2] Continuous subcutaneous infusion at 0.5 mg/kg/day for 12 weeks significantly increased tibial and vertebral bone mineral content via periosteal expansion.^[4] In glucocorticoid-treated rats, 100 mcg/kg three times daily for three months produced a four-fold increase in periosteal bone formation rate and significant recovery of muscle maximum tetanic tension.^[3] All three studies were conducted in rodents; no controlled human studies of ipamorelin's effects on bone or muscle have been published.

One Phase 2 randomized, double-blind, placebo-controlled clinical trial has been published. Beck et al. (2014; NCT00672074) enrolled 114 adults undergoing small and large bowel resection and administered ipamorelin at 0.03 mg/kg intravenously twice daily for up to seven post-operative days to study postoperative ileus.^[10] The compound was well tolerated: adverse event rates were 87.5% in the ipamorelin group versus 94.8% in the placebo group. Time to first tolerated meal was 25.3 hours in the ipamorelin group versus 32.6 hours in the placebo group — a 7.3-hour numeric improvement that did not reach statistical significance (p=0.15).^[10] Pharmacokinetic-pharmacodynamic modeling in healthy human volunteers confirmed a terminal half-life of approximately 2 hours with linear dose-proportional pharmacokinetics.^[12]

In healthy human volunteers (IV administration), ipamorelin shows a terminal half-life of approximately 2 hours, clearance of 0.078 L/h/kg, and volume of distribution at steady-state of 0.22 L/kg. GH peaks at approximately 40 minutes post-dose and returns to negligible levels within 2–3 hours. Pharmacokinetics are linear (dose-proportional) across the dose range studied.^[12] In rats, plasma clearance is approximately five-fold lower than GHRP-6, with 60–80% of an administered dose recovered as intact peptide in bile and urine — consistent with the metabolic stability conferred by the Aib N-terminal modification.^[11] Intranasal bioavailability in rats is approximately 20%.^[11]

Ipamorelin is not approved by the FDA, EMA, or any other major regulatory agency for any human therapeutic indication. Ipamorelin acetate and free base were nominated for the FDA 503A compounding bulk drug substance list (docket FDA-2024-N-4188) for proposed indications of growth hormone deficiency and postoperative ileus; the nominator withdrew the nomination in September 2024, removing it from consideration for compounding pharmacy use.^[16] Ipamorelin remains a research compound with no approved human therapeutic application.

Yes. Ipamorelin is classified as a prohibited substance under the WADA Prohibited List S2 — Peptide Hormones, Growth Factors, Related Substances and Mimetics, subcategory S2.2.4 Growth Hormone Secretagogues. The prohibition applies both in-competition and out-of-competition. No Therapeutic Use Exemption is available for competitive athletes. Detection methodology for ipamorelin metabolites in urine following both nasal and injectable administration has been established in anti-doping research.^[18]

All three compounds are GHS-R1a agonists that stimulate pulsatile GH release from pituitary somatotrophs. GHRP-2 has the highest GHS-R1a binding affinity (~0.3–0.4 nM Ki) but stimulates ACTH/cortisol and prolactin secretion at research-relevant doses. GHRP-6 shows similar GH-releasing potency to ipamorelin but also activates appetite via CD36 binding and stimulates cortisol release. Ipamorelin binds GHS-R1a at approximately 1.0–1.5 nM Ki but does not significantly stimulate ACTH, cortisol, prolactin, or TSH even at doses 200-fold above its GH-releasing ED50.^[1] Plasma clearance of ipamorelin is approximately five-fold lower than GHRP-6.^[11] In research settings, ipamorelin's cleaner selectivity profile makes it the preferred tool compound for studies requiring GH axis stimulation without confounding corticotroph activation.^[17]

Research-grade ipamorelin should meet ≥98% purity by reversed-phase HPLC, with molecular weight confirmed by LC-MS at 711.86 Da (molecular formula C38H49N9O5).^[16] A complete Certificate of Analysis should include lot number, HPLC purity percentage, amino acid analysis confirming the pentapeptide sequence, MS identity confirmation, and storage specifications. Researchers should request and review third-party COA documentation (generated by an independent analytical laboratory, not the vendor's own QC function) and should ask for the HPLC chromatogram and LC-MS spectrum rather than only the purity summary. Lyophilized powder should be stored at −20°C long-term.^[16]

Several limitations characterize the ipamorelin evidence base. First, virtually all dose-response and mechanistic data come from rodent models (rat, mouse, ferret), with the single controlled human study (Beck 2014) targeting a single GI indication and not meeting its primary efficacy endpoint.^[10] Second, long-term safety data for repeated GH pulse stimulation have not been characterized in humans; theoretical concerns include receptor desensitization, pituitary somatotroph adaptation, and GH-independent adiposity effects documented in mice.^[6] Third, the FDA 503A compounding nomination was withdrawn in September 2024, meaning there is no regulatory pathway to human therapeutic use currently active.^[16] Fourth, research-grade commercial preparations vary widely in quality; purity documentation must be independently verified.^[16]

Lall et al. (2001) found that ipamorelin and GHRP-6, administered to both GH-deficient (lit/lit) and GH-intact mice, elevated fat pad weights, serum leptin, and food intake via hypothalamic GHS-R1a activation — independently of changes in circulating GH.^[6] This is mechanistically significant: GH typically decreases fat mass via lipolysis, but GHS-R1a agonism in hypothalamic appetite circuits can increase adiposity through a GH-independent pathway. Researchers using ipamorelin to study the GH axis should be aware that not all observed body composition changes are necessarily GH-mediated.^[6]

A 2024 study in Physiology & Behavior (DOI: 10.1016/j.physbeh.2024.114644) examined ipamorelin and anamorelin in a ferret cisplatin-induced weight loss and emesis model.^[15] Intraperitoneal ipamorelin inhibited cisplatin-induced weight loss by approximately 24% during the delayed phase (48–72 hours post-cisplatin). Ipamorelin did not demonstrate significant anti-emetic effects (unlike anamorelin given intracerebroventricularly, which reduced acute emesis by 60%), indicating a peripheral weight-preservation mechanism for ipamorelin in this model. This is preclinical data in a ferret model; no clinical trials of ipamorelin in cancer-related weight loss or cachexia have been published.^[15]

CJC-1295 is a GHRH receptor agonist (activating the cAMP/PKA pathway on somatotrophs), while ipamorelin activates GHS-R1a (the Ca2+/Gq pathway). Because the two compounds act through different intracellular pathways on the same pituitary somatotroph, synergistic GH pulse amplification has been proposed in the research literature — analogous to the GH release enhancement observed with combined GHRH + GHRP administration in rodent models.^[1][17] No peer-reviewed ipamorelin + CJC-1295 combination study has been published; the rationale extrapolates from mechanistic studies of each compound individually.

Research-grade ipamorelin is distributed as a lyophilized (freeze-dried) powder to maximize shelf stability at −20°C. Before research use, it requires reconstitution in an appropriate solvent — bacteriostatic water is the standard for in vitro and in vivo peptide research. Once reconstituted, the solution should be stored at 4°C and used within a short timeframe consistent with the COA's storage specifications for the specific lot in use. Repeated freeze-thaw cycles of the reconstituted solution should be avoided.^[16]