Ipamorelin

Overview

Ipamorelin (development code NNC 26-0161) is a synthetic pentapeptide that acts as a selective agonist of the ghrelin / growth-hormone-secretagogue receptor (GHS-R1a). It was developed in the 1990s at Novo Nordisk and first described in the scientific literature by Raun and colleagues in 1998, who characterized it as "the first selective growth hormone secretagogue." Its defining feature in early research was the ability to stimulate a pulse of growth hormone (GH) release while having little effect on the release of ACTH, cortisol, or prolactin compared with earlier growth-hormone-releasing peptides (GHRPs).

Despite this favorable preclinical profile, ipamorelin was investigated in human clinical trials only to a limited extent, most notably a Phase 2 program for postoperative ileus, and was discontinued after failing to demonstrate efficacy. It has never received marketing approval from the FDA, EMA, or any other major regulatory authority for any indication.

Chemistry and structure

Ipamorelin is a short, fully synthetic peptide built largely from non-natural and D-configured amino acids, which contribute to its receptor selectivity and metabolic stability relative to naturally occurring peptides.

The sequence includes Aib (2-aminoisobutyric acid, a non-proteinogenic residue), D-2-Nal (D-2-naphthylalanine), and D-Phe (D-phenylalanine). These non-standard residues distinguish ipamorelin from endogenous ghrelin, which is a 28-residue peptide bearing an essential octanoyl (acyl) modification. Ipamorelin requires no acylation to activate the receptor.

Mechanism of action

Ipamorelin binds and activates the GHS-R1a receptor, the same receptor targeted by the endogenous hormone ghrelin and by other GHRPs such as GHRP-2 and GHRP-6. This receptor is expressed in the anterior pituitary and the hypothalamus. Activation on pituitary somatotrophs promotes the release of stored growth hormone, producing a discrete pulse of GH secretion rather than a sustained elevation.

The mechanism is distinct from that of growth-hormone-releasing hormone (GHRH) analogs such as CJC-1295, which act on the separate GHRH receptor. Because the two mechanisms are complementary, GHS-R agonists and GHRH analogs are frequently discussed together in the research literature on the GH/IGF-1 axis, though combined-use claims often circulating online go well beyond what controlled human trials have established.

The most-cited pharmacological feature of ipamorelin is its selectivity. In the original Raun et al. (1998) work, ipamorelin released GH with potency comparable to GHRP-6 but, unlike GHRP-6 and GHRP-2, did not raise plasma ACTH or cortisol above the levels seen with GHRH, even at doses far above the GH-releasing threshold. None of the secretagogues tested altered FSH, LH, prolactin (PRL), or TSH. The authors concluded that ipamorelin was the first GHRP-receptor agonist with GH selectivity resembling that of GHRH.

Research and evidence

The relatively solid animal and early pharmacology data should be kept separate from the limited human clinical evidence.

Animal and in-vitro evidence

• Selectivity and potency (Raun et al., 1998). In rat pituitary cells and in vivo (rat, swine), ipamorelin released GH with high efficacy while sparing the ACTH/cortisol axis. That was the central finding underlying its "selective" designation.
• Bone and growth models. Preclinical work has explored ipamorelin's effects on GH/IGF-1 signaling and downstream outcomes such as bone and body-weight measures in rodents. These remain animal-model findings and have not been confirmed by controlled human trials.

Human evidence

• Pharmacokinetics (Gobburu et al., 1999). This first published human PK/PD study used intravenous infusions in healthy men. PK was dose-proportional with a short terminal half-life of approximately 2 hours, and GH responses appeared as a single transient pulse. No clinically significant adverse events were reported in this small study.
• Postoperative ileus (Beck et al., 2014; NCT00672074). Sponsored by Helsinn Therapeutics, this multicenter, randomized, double-blind, placebo-controlled Phase 2 proof-of-concept study enrolled 114 patients undergoing open or laparoscopic bowel resection. Participants received IV ipamorelin 0.03 mg/kg twice daily or placebo from postoperative day 1 through day 7 or discharge. The trial did not meet its primary or secondary efficacy endpoints, although the regimen was reported as well tolerated.

There are no large, long-term, controlled human trials supporting ipamorelin for anti-aging, body composition, athletic performance, or other popularly marketed uses.

Clinical and regulatory status

Ipamorelin was carried into human clinical testing, chiefly the postoperative-ileus program, but development was discontinued after the Phase 2 results did not show efficacy. As a result:

• It has no marketing approval from the FDA, EMA, or any comparable national regulator for any indication.
• It is not a recognized prescription medication; it is distributed as a research chemical / laboratory reagent.
• In the United States, its compounding status has been the subject of FDA review. Ipamorelin is not an FDA-approved drug and was handled within the agency's bulk-drug-substance evaluations for compounding under section 503A; in 2024 the FDA addressed peptide bulk substances (including ipamorelin) through its interim 503A bulks list process and Pharmacy Compounding Advisory Committee review. Compounders are not permitted to use substances that the FDA has not placed on the approved bulks list.

Safety and reported effects

Human safety data are limited to small early-phase studies. In the Phase 1 PK/PD work and the Phase 2 ileus trial, ipamorelin was generally described as well tolerated, with no clinically significant changes reported in vital signs, ECG, or routine laboratory parameters in those settings.

Important caveats:

• The total number of humans exposed in published controlled studies is small, and follow-up was short. Long-term safety in humans is not established.
• As a GH secretagogue, theoretical and class-level concerns associated with raising GH/IGF-1 signaling (for example, effects on glucose handling, fluid retention, or unmasking of occult conditions) are relevant considerations, even though ipamorelin's selectivity spares the cortisol/ACTH axis.
• Material sold as "ipamorelin" in the research-chemical market is not subject to pharmaceutical quality control; purity, identity, and sterility cannot be assumed.

This section is descriptive, not a safety endorsement. No dosing guidance is provided.

Legal status

• United States. Not FDA-approved for human use. Sold as a research chemical and commonly labeled "not for human consumption." Not on the FDA's approved 503A bulks list for compounding.
• Anti-doping (sport). Ipamorelin is prohibited at all times (in and out of competition) under the World Anti-Doping Agency (WADA) Prohibited List, within Section S2 (Peptide Hormones, Growth Factors, Related Substances and Mimetics), which explicitly covers growth hormone secretagogues and ghrelin-receptor agonists/mimetics. Athletes in WADA-governed sport must not use it.
• General. Regulatory and legal status varies by country; the absence of approval means there is no legitimate human-therapeutic channel for it in most jurisdictions.

How it compares

Ipamorelin is most often compared with the other ghrelin-receptor agonists and the GHRH analogs covered here:

• GHRP-2 and GHRP-6 act on the same receptor but are less selective: they also stimulate cortisol, prolactin and (especially GHRP-6) appetite. Ipamorelin's distinguishing feature in the literature is its cleaner selectivity.
• CJC-1295, Sermorelin and Tesamorelin act on the separate GHRH receptor.

None of the ghrelin-agonist group is approved for human use; Tesamorelin is the only FDA-approved peptide among these GH-axis agents (HIV-associated lipodystrophy only). Ipamorelin's distinction is selectivity, not a stronger evidence base. See the Muscle & growth hormone overview.

Common misconceptions

Community claims & recent evidence

The points below address claims circulating in the peptide community — including popular video "masterclasses" that pair ipamorelin with CJC-1295 — checked against primary sources. Ipamorelin remains a research reagent with no approved human indication; nothing here is dosing or medical advice.

Verified additions

• The GH-releasing-peptide + GHRH synergy is real physiology — but old, and not demonstrated for ipamorelin specifically. In healthy men, a submaximal dose of a ghrelin-type GH-releasing peptide (GHRP-6) combined with GHRH released growth hormone synergistically (supra-additively), consistent with the two acting through independent pituitary mechanisms. [Human] (Bowers et al., J Clin Endocrinol Metab 1990). This grounds the general "they work together" idea — but the study used GHRP-6, not ipamorelin, and reports no fixed percentage.
• Ipamorelin's selectivity is demonstrated, not merely asserted. In conscious swine, ipamorelin released growth hormone with potency comparable to GHRP-6 (ED50 ≈ 2–4 nmol/kg for both), yet — unlike GHRP-6 and GHRP-2, which raised plasma ACTH and cortisol — ipamorelin did not raise ACTH or cortisol to levels significantly different from GHRH, even at doses more than 200-fold above its GH-releasing ED50. [Animal] (Raun et al., Eur J Endocrinol 1998). This is the basis for calling it the "first selective GH secretagogue."

Claims that don't hold up

• "CJC-1295 + ipamorelin give ~40% more growth hormone than either alone." No primary source supports a 40% figure for this pair. The real human synergy data (Bowers et al., JCEM 1990) used GHRP-6 + GHRH and describe supra-additive release only qualitatively; no controlled trial of CJC-1295 + ipamorelin exists. [Hypothesis]
• The cited "2018 European Journal of Endocrinology combined GHRH-and-ghrelin-agonist study that exceeded the sum of each part." This does not resolve to a locatable paper of that combination; the citation appears conflated and could not be verified against the source literature. Treated as unsupported.
• Anti-aging, immune, neurological, kidney, cardiovascular and cancer-prevention benefits attributed to "CJC-1295 + ipamorelin." These are GH/IGF-1 replacement findings — largely from recombinant growth-hormone or GH-deficiency studies — not studies of ipamorelin. Ipamorelin has no human trials for any of these outcomes, and its single efficacy trial (postoperative ileus) failed (Beck et al., Int J Colorectal Dis 2014). Attributing GH-replacement outcomes to a GH secretagogue is a category error. [Human]
• "A 1990 NEJM study (Rudman) proved GH-analogue replacement rejuvenates elderly men." Rudman et al. (N Engl J Med 1990) injected recombinant human growth hormone, not an analog or secretagogue like ipamorelin; Rudman himself stated the work carried no anti-aging implication, and later reviews flagged frequent adverse effects with no functional gain. Mischaracterized. [Human]
• "Raising GH/IGF-1 with these peptides reduces cancer risk / cannot cause cancer." Overstated and safety-relevant: there is no demonstration that ipamorelin lowers cancer risk, and elevating the GH/IGF-1 axis is not established as protective in humans. Framing it as cancer-preventive goes beyond the evidence. [Hypothesis]
• "A 2004 Journal of Endocrinology study showed ipamorelin spares cortisol and prolactin." The selectivity finding is genuine, but its primary sources are Raun et al. (Eur J Endocrinol 1998) and Gobburu et al. (Pharm Res 1999) — not a 2004 Journal of Endocrinology paper. Right fact, wrong citation.