Key points
- In swine, ipamorelin released GH without raising ACTH or cortisol, even at doses more than 200 times the ED50, unlike GHRP-6 and GHRP-2 [1].
- In healthy volunteers it produced a single GH pulse peaking at 0.67 h and had a terminal half-life of 2 hours [2].
- In rats it increased longitudinal bone growth and bone mineral content, through larger bones rather than higher volumetric density [3][4].
- Its only phase 2 trial (114 patients, postoperative ileus) showed no significant differences versus placebo, although it was well tolerated [6].
- In 2023 the FDA listed it as a substance that may present significant safety risks in 503B compounding [10].
US status (October 2026): Not FDA-approved and no compounding pathway. FDA’s advisory committee voted 0 to 12 against listing it in October 2024, and ipamorelin acetate remains in 503B Category 2. MDside providers do not prescribe it. See the ipamorelin status page.
Novo Nordisk found a cleaner secretagogue
By the late 1990s, GH-releasing peptides (GHRPs) had already shown that the pituitary could be stimulated through a pathway other than GHRH. Their story, and that of the receptor that led to the discovery of ghrelin, is told in GHRPs and ghrelin. The problem was that first-generation GHRPs also raised ACTH and cortisol. A chemistry program at Novo Nordisk in Denmark looked for a cleaner molecule and found ipamorelin: a pentapeptide (Aib-His-D-2-Nal-D-Phe-Lys-NH2) obtained by removing the central Ala-Trp dipeptide of GHRP-1 [1].
In rat pituitary cells, ipamorelin released GH with potency and efficacy similar to GHRP-6 (EC50 of 1.3 vs 2.2 nmol/L). Antagonist studies confirmed that it acts through the same receptor as the GHRPs, now known as the ghrelin receptor (GHS-R1a) [1].
Selective means no ACTH or cortisol rise in swine
The finding that named the molecule came from conscious swine. None of the secretagogues tested changed FSH, LH, prolactin or TSH. GHRP-6 and GHRP-2 raised ACTH and cortisol. Ipamorelin did not raise them to levels significantly different from those seen with GHRH. The authors described the finding as surprising, and the lack of effect held at doses more than 200 times the ED50 for GH release [1].
> “ipamorelin is the first GHRP-receptor agonist with a selectivity for GH release similar to that displayed by GHRH.” (Raun K, et al. Eur J Endocrinol. 1998 [1])
That selectivity is ipamorelin’s main theoretical advantage over other members of the class: stimulating the somatotropic axis without activating the stress axis at the same time. State its scope precisely. It is an animal finding, with maximal GH efficacy similar to GHRP-6 in swine (65 vs 74 ng/mL) [1].
- More than 200 times: the ED50 without ACTH or cortisol rise in swine [1]
- 2 h: terminal half-life in healthy volunteers [2]
- 25.3 vs 32.6 h: median time to tolerating a solid meal, ipamorelin vs placebo (p = 0.15) [6]
In humans it produces one GH pulse and clears in hours
Human pharmacokinetics were described in a dose-escalation study using 15-minute intravenous infusions at five levels (4.21 to 140.45 nmol/kg), with eight healthy men per level. Parameters were dose-proportional, with a terminal half-life of 2 hours, clearance of 0.078 L/h/kg and a volume of distribution of 0.22 L/kg [2]. Each administration produced a single episode of GH release, peaking at 0.67 hours and declining exponentially to negligible concentrations, at every dose. Between-subject variability was larger for the GH response than for pharmacokinetics [2]. The pattern is pulsatile. The long-acting analogs compared in CJC-1295, ipamorelin and MK-677 produce a sustained rise instead.
The bone and body composition data come from rodents
In adult female rats treated for 15 days, ipamorelin dose-dependently increased the longitudinal growth rate of the tibia from 42 to 52 µm/day (P < 0.0001), as well as body-weight gain. It did not change total IGF-I or serum bone-turnover markers [3]. In a 12-week rat study using subcutaneous minipumps, ipamorelin and GHRP-6 increased bone mineral content measured by DXA. Detailed analysis showed that the increase was due to larger bones. Volumetric mineral density did not change, nor did mineral content corrected for body weight [4].
Body composition adds a rarely cited nuance. In mice, ipamorelin increased fat-pad weight relative to body weight, in both GH-intact and GH-deficient animals. In GH-intact mice the secretagogues, unlike GH, increased leptin and food intake. The authors concluded that secretagogues increase body fat through GH-independent mechanisms that may include increased feeding [5]. The effect on the ghrelin receptor reaches beyond GH release.
The clinical bet was postoperative ileus
The ghrelin receptor is not only in the pituitary. Its stimulation has promotility effects in the upper and lower gastrointestinal tract [6], and that was the clinical bet: ipamorelin was developed, sponsored by Helsinn Therapeutics, for postoperative ileus, a common complication after bowel surgery [11].
The preclinical data were encouraging. In rats undergoing laparotomy and intestinal manipulation, a single intravenous dose of ipamorelin shortened the time to first bowel movement, and repeated dosing increased fecal output, food intake and weight gain [7]. In the same model, surgery left 78% of a meal in the stomach of control animals versus 52% with ipamorelin (44% in non-operated animals), and the molecule reversed the loss of gastric muscle contractility through a cholinergic, ghrelin-receptor-mediated mechanism [8].
The phase 2 trial missed its endpoint
The phase 2 trial was multicenter, double-blind and placebo-controlled, in adults undergoing open or laparoscopic small- or large-bowel resection. They received intravenous infusions of ipamorelin 0.03 mg/kg or placebo twice daily, from postoperative day 1 to day 7 or discharge. The key endpoint was time from first dose to tolerance of a standardized solid meal [6].
A total of 117 patients were enrolled, 114 of whom made up the safety and analysis populations. Median time to first tolerated meal was 25.3 hours with ipamorelin and 32.6 hours with placebo (p = 0.15): a difference of about seven hours in the drug’s favor that was not statistically significant. There were no significant differences in key or secondary endpoints. Adverse events occurred in 87.5% with ipamorelin and 94.8% with placebo, and the authors concluded the drug was well tolerated. They noted as a limitation that the study was small and enrolled patients with a broad range of conditions [6].
The result was not unique to ipamorelin. Ulimorelin, another ghrelin-receptor agonist, was tested in two phase 3 trials of 332 and 330 patients after bowel resection, and it also failed to beat placebo on the primary or secondary endpoints [9]. Postoperative ileus proved a difficult target for the whole class.
The evidence stops short of the uses patients ask about
Ipamorelin has no published human trials on body composition, muscle recovery or aging. Its clinical development focused on ileus, and the bone and growth effects come from rats [3][4][6]. Selectivity for ACTH and cortisol was shown in animals, not in repeated-dose human trials [1].
In September 2023, the FDA added it to its list of bulk substances that may present significant safety risks in compounding, under category 2 of the 503B policy. It cited a possible immunogenicity risk from aggregation or impurities, and the complexity of characterizing a peptide with unnatural amino acids. It also wrote: “A study published in literature identified serious adverse events including death when ipamorelin was administered intravenously for improving gastric motility,” and that “FDA has not identified safety-related information regarding ipamorelin acetate via certain other injectable routes of administration” [10]. The FDA entry does not identify the study or detail the cause of that death. The published abstract of the phase 2 trial reports fewer adverse events with ipamorelin than with placebo [6][10].
What to tell patients who ask
In the available animal data, ipamorelin is the GH secretagogue with the cleanest hormonal profile compared with the GHRPs it was tested against (GHRP-6 and GHRP-2) [1]. Its basic human pharmacology is published [2], and its only clinical trial showed a favorable, non-significant trend with good tolerability [6]. Those are the arguments its supporters make, and they are real. Patients also need to hear what has not been measured: no human trial for the uses it is marketed for, and an FDA safety listing that blocks compounding. If a patient brings a vial from an online seller, read what research-use-only labeling means and are peptides legal before the conversation. For the programs MDside supports, see peptide programs.
References
- Raun K, et al. Ipamorelin, the first selective growth hormone secretagogue. Eur J Endocrinol. 1998;139(5):552-61. PMID 9849822. Link
- Gobburu JV, et al. Pharmacokinetic-pharmacodynamic modeling of ipamorelin, a growth hormone releasing peptide, in human volunteers. Pharm Res. 1999;16(9):1412-6. PMID 10496658. Link
- Johansen PB, et al. Ipamorelin, a new growth-hormone-releasing peptide, induces longitudinal bone growth in rats. Growth Horm IGF Res. 1999;9(2):106-13. PMID 10373343. Link
- Svensson J, et al. The GH secretagogues ipamorelin and GH-releasing peptide-6 increase bone mineral content in adult female rats. J Endocrinol. 2000;165(3):569-77. PMID 10828840. Link
- Lall S, et al. Growth hormone (GH)-independent stimulation of adiposity by GH secretagogues. Biochem Biophys Res Commun. 2001;280(1):132-8. PMID 11162489. Link
- Beck DE, et al. Prospective, randomized, controlled, proof-of-concept study of the Ghrelin mimetic ipamorelin for the management of postoperative ileus in bowel resection patients. Int J Colorectal Dis. 2014;29(12):1527-34. PMID 25331030. Link
- Venkova K, et al. Efficacy of ipamorelin, a novel ghrelin mimetic, in a rodent model of postoperative ileus. J Pharmacol Exp Ther. 2009;329(3):1110-6. PMID 19289567. Link
- Greenwood-Van Meerveld B, et al. Efficacy of ipamorelin, a ghrelin mimetic, on gastric dysmotility in a rodent model of postoperative ileus. J Exp Pharmacol. 2012;4:149-55. PMID 27186127. Link
- Shaw M, et al. Safety and efficacy of ulimorelin administered postoperatively to accelerate recovery of gastrointestinal motility following partial bowel resection: results of two randomized, placebo-controlled phase 3 trials. Dis Colon Rectum. 2013;56(7):888-97. PMID 23739196. Link
- U.S. Food and Drug Administration. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks (ipamorelin acetate, 29 September 2023). Link
- ClinicalTrials.gov. NCT00672074: Safety and Efficacy of Ipamorelin for Management of Post-Operative Ileus (sponsor: Helsinn Therapeutics). Link
This is general information, not medical or legal advice. Rules vary by state and change. Confirm your own facts with counsel.