Ipamorelin.

Ipamorelin is a research compound in the growth-hormone secretagogues.

Acting on the ghrelin / GH-secretagogue receptor to release growth hormone.

It draws interest for growth-hormone secretagogues.

F-tier evidence: human evidence is limited; most support is preclinical.

What it is

Ipamorelin is a synthetic pentapeptide (Aib-His-D-2-Nal-D-Phe-Lys-NH2) belonging to the growth hormone-releasing peptide (GHRP) class, sometimes described as a "third-generation" GHRP. Derived from the earlier secretagogue GHRP-1, it acts as a ghrelin mimetic and was characterized by Novo Nordisk researchers in the late 1990s as the first GHRP-receptor agonist with selectivity for growth hormone (GH) release approaching that of GHRH. It has no approved therapeutic indication and exists as an investigational/research compound.

How it works

Ipamorelin is a selective agonist of the growth hormone secretagogue receptor type 1a (GHS-R1a), the same G-protein-coupled receptor activated by the endogenous hormone ghrelin. Binding at the pituitary (and hypothalamus) triggers GH release through a GHRP-like pathway distinct from, but synergistic with, GHRH signaling; pharmacological profiling with GHRH and GHRP antagonists showed its action is mediated via the GHRP-type receptor rather than the GHRH receptor. Its defining feature is selectivity: in the original characterization it released GH with potency comparable to GHRP-6 but, unlike older GHRPs, did not meaningfully raise ACTH, cortisol, FSH, LH, prolactin, or TSH, even at doses far above the ED50 for GH release.

What the evidence shows

The foundational evidence is preclinical: Raun et al. (Eur J Endocrinol, 1998) characterized ipamorelin in rats and isolated pituitary cells, establishing GH selectivity over ACTH/cortisol and other pituitary hormones. Subsequent animal work explored non-endocrine effects via GHS-R1a—e.g., Venkova et al. (J Pharmacol Exp Ther, 2009) reported prokinetic/anti-ileus activity in a rodent model of postoperative ileus. The principal human data come from a single industry-sponsored (Helsinn Therapeutics) randomized, double-blind, placebo-controlled proof-of-concept trial in bowel-resection patients (Beck et al., Int J Colorectal Dis, 2014; ClinicalTrials.gov NCT00672074), where the primary composite gastrointestinal-recovery endpoint did not reach statistical significance, though some secondary measures trended favorably. There are no large, controlled human trials demonstrating efficacy for muscle growth, anti-aging, fat loss, bone density, or body composition in people; widely repeated claims in those areas rest on mechanism and animal data, not human outcome trials, and the postoperative-ileus program did not advance to Phase III.

Safety considerations

Human safety data are limited to small, short-duration trials; the bowel-resection study used intravenous administration in a hospital setting and did not establish a long-term safety profile. As a GH/IGF-1-axis stimulant, plausible class-related concerns include effects on insulin sensitivity and blood glucose, fluid retention, and theoretical risks tied to chronically elevated GH/IGF-1 (e.g., relevant to people with cancer or active proliferative conditions), though these have not been well characterized for ipamorelin specifically in humans. Because much non-clinical material is produced as unregulated "research chemical" powder, real-world risks also include impurity, mislabeling, and lack of sterility/quality control. Long-term consequences of repeated use in humans are essentially unknown.

Regulatory status

Ipamorelin is not approved by the FDA (or other major regulators) for any indication; it remains an investigational/research-use compound and was the subject of FDA pharmacy-compounding review activity rather than drug approval. It is prohibited in sport by the World Anti-Doping Agency at all times as a growth hormone secretagogue under category S2 (Peptide Hormones, Growth Factors, and Mimetics).

1. [1]Ipamorelin, the first selective growth hormone secretagogue — European Journal of Endocrinology, 1998; Raun K, et al.; PMID 9849822
2. [2]Prospective, randomized, controlled, proof-of-concept study of the ghrelin mimetic ipamorelin for the management of postoperative ileus in bowel resection patients — International Journal of Colorectal Disease, 2014; Beck DE, et al.; PMID 25331030 (NCT00672074)
3. [3]Efficacy of ipamorelin, a novel ghrelin mimetic, in a rodent model of postoperative ileus — Journal of Pharmacology and Experimental Therapeutics, 2009; Venkova K, et al.; PMID 19289567
4. [4]WADA Prohibited List (category S2: Peptide Hormones, Growth Factors, Related Substances and Mimetics) — World Anti-Doping Agency, current Prohibited List

• Not FDA-approved; research-only.
• Long-term human safety is not established.

Stack fit

Why not D: held back by human evidence, safety clarity, regulatory clarity, practical relevance.

What would move it up: Larger controlled human trials, clearer long-term safety, replicated findings, and regulatory progress.

What would move it down: Failed confirmatory trials, new safety signals, or evidence that popular claims don't translate.

• Ipamorelin is not FDA-approved for human use; it is discussed in a research context.
• It belongs to the Growth-hormone secretagogues class.
• Its principal mechanism is characterized in the literature.

• Whether observed effects reliably translate to humans at large.
• Long-term safety in healthy users, and full drug-interaction risk.
• Optimal studied parameters outside any approved indication.
• Claim-by-claim verdicts — these are authored against verified sources and shown when complete.
• Quality and purity of material from non-pharmaceutical sources.

1. What it is
2. The Ghrelin-receptor agonism mechanism
3. The preclinical evidence lane
4. Why Preliminary, and not higher or lower
5. Proven lane vs speculative lane
6. What people report
7. Regulatory status
8. What changed recently