Ipamorelin: The Selective Secretagogue That Failed Its Only Published Human Trial

Ipamorelin is sold as the clean growth hormone secretagogue. It reached human trials twice, for postoperative ileus, and the published trial missed its primary endpoint at p = 0.15. The larger one, with 320 patients, never reported results at all.

That record is the thing missing from almost every page written about this pentapeptide. Ipamorelin sits in the growth hormone peptides category, is usually met inside a stack that has its own CJC-1295 and ipamorelin calculator, and is defended on a selectivity finding that was produced in pigs. This article works through the trial documents, the 1998 animal paper and the FDA advisory committee file in that order.

Has ipamorelin ever worked in a human trial?

No. Ipamorelin has been tested in two registered Phase 2 trials, both for postoperative ileus, and neither produced a positive published result. The one that reported, Beck et al. 2014 in 117 bowel-resection patients, missed its primary endpoint: 25.3 hours to tolerating a solid meal on ipamorelin versus 32.6 hours on placebo, p = 0.15. The larger trial, NCT01280344, enrolled 320 patients, completed in May 2014, and has never posted results.

The Beck trial was randomised, double-blind and placebo-controlled, dosing 0.03 mg/kg intravenously twice daily in International Journal of Colorectal Disease. The authors did not soften it. Their own summary reads: "there were no significant differences between ipamorelin and placebo."

NCT01280344 was the bigger swing — a Phase 2 dose-finding study in the same indication, sponsored by Helsinn Therapeutics, running April 2011 to May 2014. Registry status: Completed. Results not posted. No publication was located.

A completed 320-patient trial whose results were never released is itself information. It is not what a positive result usually looks like. Across the two studies, the public record contains one negative endpoint and one silence.

What is ipamorelin, and how does it differ from the other ghrelin-receptor peptides?

Ipamorelin is a synthetic pentapeptide, Aib-His-D-2-Nal-D-Phe-Lys-NH₂, with a molecular weight of 711.9 g/mol and CAS number 170851-70-4. Novo Nordisk developed it as NNC 26-0161. It agonises GHS-R1a, the ghrelin receptor, and has a human intravenous half-life of about two hours. Unlike GHRP-2, GHRP-6 and hexarelin, it carries no Trp-Trp core; it uses Aib and D-2-naphthylalanine instead, making it the chemical outlier of the class.

Two structural notes carry consequences. The absent Trp-Trp core is why the selectivity profile differs from its neighbours at all — this is a genuinely different molecule, not a tweak. And at 711.9 Da it is 106 to 175 Da lighter than the other three, which makes it the easiest member of the class to confirm by mass.

The class comparison is where most buyers actually start, and it is the fastest way to see what is distinctive about each member.

For a direct head-to-head of the three ghrelin mimetics buyers most often confuse, see GHRP-2 vs GHRP-6 vs ipamorelin.

Is ipamorelin's selectivity real, or is it a pig study?

Ipamorelin's selectivity is real and it was demonstrated in conscious swine, not in people. Raun et al. 1998, working at Novo Nordisk, showed that GHRP-6 and GHRP-2 raised ACTH and cortisol while ipamorelin did not, even at doses more than 200-fold above its own GH ED₅₀. No secretagogue tested altered FSH, LH, prolactin or TSH. No human study measuring cortisol or prolactin after ipamorelin was located, so the headline claim rests entirely on animal data.

The founding paper, "Ipamorelin, the first selective growth hormone secretagogue" in European Journal of Endocrinology, is a good piece of work and it is entirely animal work. In rat pituitary cells, ipamorelin's EC₅₀ was 1.3 ± 0.4 nmol/L against GHRP-6's 2.2 ± 0.3. In anaesthetised rats, ED₅₀ was 80 ± 42 nmol/kg versus GHRP-6's 115 ± 36. The authors concluded that ipamorelin was "the first GHRP-receptor agonist with a selectivity for GH release similar to that displayed by GHRH."

The problem is not the swine experiment. It is the comparison built on top of it. Ipamorelin's cortisol behaviour is known from pigs; GHRP-2's and GHRP-6's is known from humans. "Cleaner than GHRP-2" is therefore a cross-species inference, not a measured difference, and it is the single most repeated sentence written about this compound.

How much growth hormone does ipamorelin release in humans?

Ipamorelin released growth hormone in exactly one published human study. Gobburu et al. 1999, in Pharmaceutical Research, gave eight healthy males five escalating intravenous infusions. Terminal half-life was about two hours, kinetics were dose-proportional, and growth hormone came out as a single episode peaking at 0.67 hours after every dose. Inter-individual variability in response exceeded variability in drug levels. That n=8 study is the entire human GH-release dataset: single doses, intravenous, no clinical endpoint.

The variability finding deserves a sentence of its own. People differed more in how much growth hormone they released than in how much drug was circulating, which means the dose is not the main variable in the response. Nothing in the human record identifies what the main variable is.

Worth remembering how this class arrived: the molecules came before the biology. The receptor was cloned in 1996 — Howard et al., "A receptor in pituitary and hypothalamus that functions in growth hormone release" in Science — and that paper explicitly proposed that the growth hormone secretagogues "mimic an undiscovered hormone." The hormone surfaced three years later in the stomach: Kojima et al., "Ghrelin is a growth-hormone-releasing acylated peptide from stomach" in Nature, a 28-amino-acid peptide whose serine-3 residue is n-octanoylated, an acylation essential for activity. So the accurate framing is not that ipamorelin mimics ghrelin; it is that synthetic peptides were found to release GH, the receptor was located afterwards, and the natural ligand afterwards again.

Why did FDA's advisory committee vote 0–12 against ipamorelin?

FDA's Pharmacy Compounding Advisory Committee reviewed ipamorelin on 29 October 2024 and voted 0 in favour, 12 against, with 1 abstention, on both the free base and the acetate. The briefing document states that FDA identified no data supporting effectiveness for growth hormone deficiency or for postoperative ileus, flagged possible behavioural reinforcing properties and reproductive effects arising from ghrelin receptor agonism, and called the free base poorly characterised on impurities, aggregates and endotoxin.

The document is unusually direct for a regulatory filing:

• "FDA has not identified data to support the effectiveness of ipamorelin… for the diagnosis or treatment of GHD."

• "FDA has not identified data to support the effectiveness of ipamorelin… for postoperative ileus. The only published study… did not show significant differences between ipamorelin and placebo."

• "Due to its primary mechanism of action as a ghrelin receptor agonist, ipamorelin… may have behavioral reinforcing properties, which can contribute to development of addiction, and may also negatively affect reproductive health."

• Ipamorelin free base is "not well-characterized from the physical and chemical characterization perspective" — missing impurities, aggregates and endotoxin data.

Ipamorelin acetate remains on FDA's Category 2 list for 503B outsourcing facilities, added 29 September 2023 on immunogenicity and aggregation grounds, with the page current as of 22 April 2026. That status matters because it diverges from where most peptides on this site now sit. Ipamorelin was not among the substances whose nominations were withdrawn in April 2026, and it was not on the July 2026 PCAC agenda that advanced BPC-157, KPV, TB-500, MOTS-c, Semax and Epitalon. It stayed on the active list while others moved. Our FDA peptide regulation timeline tracks those movements in order.

In sport, ipamorelin is named explicitly at S2.2.4 of WADA's 2026 Prohibited List, under growth hormone secretagogues and their mimetics: prohibited at all times, non-specified.

What ipamorelin dose has actually been tested in people?

No validated human dosing protocol for ipamorelin exists. The only published human exposures are single escalating intravenous infusions in an eight-man pharmacokinetic study and 0.03 mg/kg intravenously twice daily in the failed ileus trial. Neither supports the 200–300 mcg subcutaneous convention circulating in community protocols. The pharmacologically relevant facts are the two-hour half-life and the single GH pulse per dose: ipamorelin is short-acting, and its effect is one release episode rather than sustained elevation.

Both published exposures were intravenous. The route everyone actually uses has never been characterised in a published trial, which means bioavailability, timing and the shape of the GH curve after a subcutaneous injection are all extrapolations.

For the reconstitution arithmetic itself, use the CJC-1295 and ipamorelin calculator alongside the reconstitution calculator. Those tools answer a volume question, not a dose-selection question, and nothing in the literature answers the second.

Does pairing ipamorelin with CJC-1295 add anything measurable?

No controlled human trial has quantified the ipamorelin plus CJC-1295 combination. The mechanistic rationale is genuine: GHRH-R and GHS-R1a are separate receptors on the same pituitary somatotrophs, and the 1990 work on growth hormone releasing peptides showed synergy between the two pathways. What does not exist is a number. The specific synergy percentages circulating for this stack have no source, which leaves the pairing a mechanistic argument rather than a measured effect.

The standard stack pairs ipamorelin with a GHRH analogue such as CJC-1295 without DAC, and the two-receptor logic is why it caught on. That logic is sound as far as it goes. It simply has not been converted into a controlled comparison in humans.

Reduce your expectations of any percentage you see quoted for this combination if the source is a forum post or a vendor page rather than a trial. Further reading: the CJC-1295 and ipamorelin stack guide and the CJC-1295 and ipamorelin blend page.

Which ipamorelin claims survive the evidence?

Exactly one ipamorelin claim is established in humans, and it is narrow: that ipamorelin releases growth hormone, on an eight-man intravenous pharmacokinetic study. The absence of cortisol and prolactin rise is animal-only. Clinical effectiveness failed, with one randomised trial missing its endpoint at p = 0.15 and a 320-patient trial going unreported. Lean mass, fat loss, sleep and recovery have no human study behind them, and the "Phase III validated" claim is simply false.

One citation to avoid. A paper titled "Ipamorelin for postoperative ileus: results of phase II/III trials" circulates attributed to PMID 11600700. That PMID is "The role of acetylation in rDNA transcription," a 2001 molecular biology paper in Nucleic Acids Research. No phase II/III ipamorelin publication exists. If a vendor page cites it, that page was not fact-checked.

How do you verify ipamorelin before you buy it?

Ipamorelin's identity risk is low by the standards of its class: at 711.3857 monoisotopic it sits 106 to 175 Da below GHRP-2, GHRP-6 and hexarelin, so any mass spectrometer separates them. The realistic risks are underfill and non-peptide bulking, not substitution. Four checks cover it — mass spectrometry for identity, net peptide content for quantity, third-party HPLC for purity, and an LAL endotoxin result, which FDA specifically flagged as missing from the compounding submission.

Ipamorelin is among the better-covered compounds on this platform. The Purity Index records an index of 99.65 across 323 recency-weighted tests from 21 laboratories (verified August 2026), against a platform composite of 99.50. The ipamorelin compound page shows 407 total tests averaging 99.66% across 229 shops (verified August 2026) — the larger figure because the index applies recency weighting and exclusions. Ipamorelin price data shows 63 shops in stock, a median of $6.00/mg and a low of $2.00/mg on a 10 mg vial (verified August 2026), a 7× spread across comparable offers. Those figures exclude shipping, taxes and customs, coupon codes, bulk tiers, multi-vial kits and account-gated pricing.

That evidence base sits inside a platform tracking 530 shops and 11,852 independent lab tests across 118 peptides (verified August 2026). Method reading: mass spectrometry for peptides, why 10 mg isn't 10 mg, and where to buy ipamorelin with purity and identity checks.

The trial that would settle this

The trial that would settle ipamorelin does not exist, and its shape is easy to specify: a subcutaneous, community-dose, months-long randomised study with a clinical endpoint rather than a GH curve, measuring cortisol and prolactin in humans, against GHRP-2 or hexarelin head-to-head. Every human exposure so far has been intravenous, acute and short. The selectivity claim that defines this compound has never been tested in people, and a 320-patient trial has sat unreported since 2014.

Frequently Asked Questions

Is ipamorelin really selective?

In pigs, yes. Raun et al. found no rise in ACTH or cortisol even at doses more than 200 times the GH-releasing dose, and no change in FSH, LH, prolactin or TSH. In humans, nobody has measured it. The familiar comparison against GHRP-2 and GHRP-6 mixes animal data for ipamorelin with human data for the others.

Has ipamorelin worked in a human trial?

No. The one published randomised controlled trial, in 117 postoperative patients, missed its primary endpoint at p = 0.15, with 25.3 hours to a solid meal versus 32.6 on placebo. A larger 320-patient Phase 2 trial completed in May 2014 and has never reported results.

Can ipamorelin be compounded legally?

No. FDA's Pharmacy Compounding Advisory Committee voted 0 in favour, 12 against, 1 abstention on both the free base and the acetate in October 2024. Ipamorelin acetate remains on the Category 2 significant-safety-risk list, added 29 September 2023 and still current as of 22 April 2026.

Is ipamorelin banned in sport?

Yes. It is named explicitly at section S2.2.4 of WADA's 2026 Prohibited List under growth hormone secretagogues and their mimetics, prohibited at all times and classified as non-specified.

How long does ipamorelin act?

The terminal half-life is about two hours in humans after intravenous dosing, and the growth hormone response is a single episode peaking around 0.67 hours after the dose. It is short-acting by design, and repeated dosing has never been characterised in a published human study.

Could ipamorelin be swapped for another GHRP in the vial?

Not undetectably. It is 106 to 175 Da lighter than GHRP-2, GHRP-6 and hexarelin, and it is the only member of the group without the Trp-Trp core, so any mass spectrometry run separates them. Underfill and non-peptide bulking are the more realistic problems.

Where this leaves ipamorelin

Ipamorelin has the cleanest pharmacological story in its class and the weakest clinical record in it. The receptor pharmacology is solid, the 1998 selectivity finding is real, and the animal work behind it holds up. What it does not have is a single positive human outcome: one randomised trial missed its endpoint, one 320-patient trial has never reported, and an FDA advisory committee reviewed the whole file and found no vote in its favour.

That is still more information than most peptides on this site come with. A real sponsor took ipamorelin into real trials for a real indication, and the answer came back negative or silent. Buyers are entitled to weigh that against a selectivity claim that has only ever been measured in pigs.

Browse the growth hormone peptides category, or our complete peptide guide with 118 compounds (verified August 2026). For per-injection volume, use the CJC-1295 and ipamorelin calculator alongside the reconstitution calculator. Compare shops through independent lab tests and community-verified shop reviews.

This article is for educational and informational purposes only and does not constitute medical advice. Peptides discussed may be investigational compounds not approved by the FDA (or equivalent regulators in your jurisdiction) for human use. Always consult a qualified healthcare provider before using any peptide or research compound. Peptigrity is an independent review platform and does not sell, endorse, or recommend specific products or vendors.