Ipamorelin

Ipamorelin is a synthetic pentapeptide (Aib-His-D-2-Nal-D-Phe-Lys-NH2) that binds the ghrelin receptor and makes the pituitary release a pulse of the body's own growth hormone (GH). Synthesized at Novo Nordisk in the mid-1990s, it entered the literature in 1998 as "the first selective growth hormone secretagogue" (Raun et al., Eur J Endocrinol 1998).

Evidence tier: preclinical, with an abandoned clinical program. Most gray-market peptides never had a sponsor, a registered trial, or a regulatory file; ipamorelin had all three. Helsinn Therapeutics took it into phase 2 for postoperative ileus — the temporary shutdown of gut motility after abdominal surgery — and in 117 bowel-resection patients, intravenous ipamorelin beat placebo on neither its primary nor any secondary endpoint (Beck et al., Int J Colorectal Dis 2014). A 320-patient dose-finding study finished in 2014 (NCT01280344) and never posted results or produced a publication. There was no phase 3 and no approval anywhere.

Read it as a pharmacological success and a therapeutic non-event: the molecule does what it was designed to do to hormone levels, and the one time that was tested against a human clinical outcome, it changed nothing.

Ipamorelin is an agonist at the growth hormone secretagogue receptor (GHS-R1a) — the receptor for ghrelin, the stomach-derived "hunger hormone." Activating it in the hypothalamus and pituitary amplifies the body's own pulsatile GH output rather than supplying GH from outside, as recombinant somatropin does. Its ceiling is therefore whatever the pituitary can be persuaded to secrete.

The word doing the work in "selective growth hormone secretagogue" is selective. In the original characterization, ipamorelin released GH from rat pituitary cells with potency close to GHRP-6 (EC50 1.3 vs 2.2 nmol/L), but with a strikingly narrow hormonal footprint (Raun 1998):

• No release of ACTH or cortisol above what GHRH itself produced — even at doses more than 200 times the dose needed to release GH.

• No significant change in FSH, LH, prolactin, or TSH.

That is the whole basis of the selectivity claim repeated across vendor copy: a real finding, in animals. It is also what separates ipamorelin from GHRP-2 and GHRP-6, which are more prone to nudging prolactin and cortisol upward and, for GHRP-6, provoking hunger.

In humans the resulting signal is brief — one GH episode per dose, gone within hours (Gobburu et al., Pharm Res 1999).

Ipamorelin has no approved indication anywhere and is not a component of any FDA-approved drug. The two uses seriously pursued were growth hormone deficiency (GHD) and postoperative ileus (POI); the FDA reviewed both in 2024 after compounding pharmacies nominated ipamorelin for the list of bulk substances usable in compounded medicines (FDA briefing document, August 2024).

• Postoperative ileus. The phase 2 trial gave 0.03 mg/kg intravenous ipamorelin or placebo twice daily from postoperative day 1 to day 7 or discharge. Median time to tolerating a standardized solid meal was 25.3 hours vs 32.6 on placebo — not significant (p = 0.15) — with no significant differences in the key or secondary analyses either (Beck 2014). FDA's reviewers quoted the published verdict on the program: "due to these disappointing results, its development was discontinued."

• Growth hormone deficiency. FDA identified no data supporting effectiveness for diagnosing or treating GHD at any age, and noted guidelines do not mention it. A mechanistic catch compounds this: a secretagogue needs a pituitary that can still secrete, so patients with complete GHD do not respond to these agents at all.

On 29 October 2024, FDA's Pharmacy Compounding Advisory Committee voted against adding ipamorelin to the 503A bulk substances list — 0 in favour, 12 against, 1 abstention, free base and acetate alike — citing "a lack of information supporting safety and efficacy" (PCAC minutes). The same meeting voted down ibutamoren (MK-677).

What ipamorelin is sold for resembles neither indication: FDA catalogued marketing for weight loss, anti-aging, inflammatory conditions, sleep, and bodybuilding — categories with no ipamorelin trials behind them.

As a growth hormone secretagogue, ipamorelin is prohibited in and out of competition under Section S2 of the WADA Prohibited List, alongside GHRPs, GHRH analogues such as sermorelin and CJC-1295, and GH itself. The prohibition is enforceable: laboratories have published validated urine methods tracking ipamorelin and its metabolites, with Ipamorelin (1-4) free acid detectable after the parent compound has cleared (Semenistaya et al., Drug Test Anal 2015).

Documented sanctions include:

• David Branch (UFC): a two-year sanction after ipamorelin was found in an out-of-competition urine sample collected 24 May 2019 (USADA sanction announcement).

• Andrew McKirahan (MLB): an 80-game suspension in 2015 after testing positive for ipamorelin (ESPN, April 2015).

Sourcing adds risk on top: analysis of seized "growth promoting" black-market products identified Gly-ipamorelin — an extra N-terminal glycine — rather than ipamorelin itself (Krug et al., Growth Horm IGF Res 2018). A designer analogue is no less prohibited.

The only controlled human safety dataset of any size is the postoperative ileus trial, in 114 patients recovering from bowel surgery. Most adverse events were mild to moderate and surgery-related, at similar overall rates (87.5% vs 94.8% on placebo), but FDA's review flagged imbalances (FDA 2024; Beck 2014):

• Hyperglycemia at discharge: 14.3% vs 8.6% on placebo.
• Hypokalemia: 12.5% vs 3.4%. Insomnia: 10.7% vs 5.2%.

• Serious adverse events: 17.9% vs 15.5%, including two deaths in the ipamorelin arm, both in colon-cancer patients with postoperative complications. A trial this size, in a population this sick, cannot resolve causality either way.

Outside that trial the record is nearly empty: FDA's search of the FAERS adverse-event database through September 2023 returned two non-serious reports — an absence of reporting, not a clean record.

The predictable concerns come from the class. A review of GH secretagogues found them generally well tolerated but flagged rising blood glucose from decreased insulin sensitivity, and called for long-term evaluation of cancer incidence and mortality (Sigalos & Pastuszak, Sex Med Rev 2018). In the class's longest trial — two years of MK-677 in 65 older adults — fasting glucose rose about 5 mg/dL, insulin sensitivity fell, and edema and muscle pain were common (Nass et al., Ann Intern Med 2008).

FDA's non-clinical reviewers added what marketing omits: as a ghrelin-receptor agonist, ipamorelin "may have behavioral reinforcing properties" and "may also negatively affect reproductive health and pregnancy outcomes," no published study informs its carcinogenic potential, and the toxicology overall is "too limited in scope and duration."

Ipamorelin is short-acting: a terminal half-life near 2 hours, a GH peak around 40 minutes, GH near baseline by 6 hours (Gobburu 1999). Every published human PK/PD dataset used intravenous dosing; FDA stated in 2024 that it found no PK or PD information for the subcutaneous route — the one essentially all non-clinical use relies on.

Because GHS agents depend on pituitary responsiveness, FDA's reviewers also raised the concern that it may fall as GH stores deplete — the mechanistic version of the tolerance community logs describe.

Ipamorelin is supplied as a lyophilized powder for reconstitution. With no USP monograph for either form, FDA's chemists called it "not well characterized": vendor certificates of analysis typically report purity only, nothing on impurities, aggregates, or endotoxins — the gaps that drive immunogenicity risk in an injected peptide (FDA 2024).

The most common pairing is with a GHRH analogue, on the theory that pulling two levers of the same axis produces a larger pulse than either alone — FDA's review recorded clinicians calling this a "trending synergistic combination" with CJC-1295. No controlled human trial of it has been published.

• CJC-1295 + Ipamorelin — the blend.
• CJC-1295 with DAC — the long-acting GHRH analogue.
• Sermorelin — the GHRH fragment that once held an approval.
• GHRP-2 and MK-677 — the less selective and the oral relatives.

Around 50 PubMed-indexed papers mention ipamorelin. The arc is consistent: clean animal pharmacology, one negative human trial.

• Characterization (1998): selective GH release with no significant ACTH, cortisol, prolactin, LH, FSH, or TSH response in rats and swine (Eur J Endocrinol 1998).

• Bone (rats): 15 days of dosing raised longitudinal bone growth from 42 to 52 µm/day without changing IGF-1 (Growth Horm IGF Res 1999); 12 weeks of infusion raised bone mineral content via larger bone dimensions, volumetric density unchanged (J Endocrinol 2000).

• Gut motility (rats): repeat dosing after surgery increased fecal output, food intake, and weight gain — the result that justified the clinical program (J Pharmacol Exp Ther 2009).

• Humans: dose-proportional kinetics and one GH episode per dose in 48 healthy men (Pharm Res 1999); no efficacy signal in 114 randomized bowel-resection patients (Int J Colorectal Dis 2014); an FDA advisory committee vote of 0–12 against compounding-list inclusion (PCAC minutes, October 2024).

Nothing here tests body composition, recovery, sleep, or aging in humans; those claims extrapolate from GH biology. For a fuller walkthrough, see the ipamorelin research and evidence overview.

For deeper dives on this peptide, see:

• Ipamorelin benefits and areas of interest
• Ipamorelin side effects and safety context
• Ipamorelin dosing concepts (educational)
• Ipamorelin research and evidence overview

Is ipamorelin FDA-approved? No. It has no approved indication anywhere and is not a component of any approved drug. In October 2024 an FDA advisory committee voted 0–12 (1 abstention) against allowing it on the 503A list of substances that compounding pharmacies may use, citing a lack of information supporting safety and efficacy (PCAC minutes).

What does "selective" actually mean? One specific finding: ipamorelin released GH without raising ACTH or cortisol above the level GHRH itself produced — even at 200 times the GH-releasing dose — and without moving prolactin, LH, FSH, or TSH (Raun 1998). That is a claim about hormonal side effects in animals, not a claim that it releases more GH, and not a claim of benefit.

Ipamorelin vs CJC-1295 — what's the difference? Different receptors. Ipamorelin is a ghrelin-receptor (GHS-R1a) agonist producing a GH pulse lasting hours; CJC-1295 is a GHRH analogue, the DAC version engineered to circulate for days — which is why they are marketed together as a blend. No controlled human trial of the combination has been published.

Ipamorelin vs sermorelin? Different receptors again: sermorelin is a GHRH fragment, and unlike ipamorelin it once held an approval — FDA's 2024 review notes that "only sermorelin (Geref, NDA 020443) was approved for the treatment of short stature associated with GHD in pediatric patients," a product no longer marketed in the US (FDA 2024). Both depend on a pituitary that can still respond, so neither works in complete GH deficiency.

Why did its clinical development stop? Lack of efficacy, not a safety scandal. The phase 2 ileus trial missed its primary endpoint (25.3 vs 32.6 hours to meal tolerance, p = 0.15) and every secondary endpoint (Beck 2014), and the 320-patient dose-finding study that followed (NCT01280344) never posted results or produced a publication.

Is ipamorelin banned in sport? Yes — prohibited at all times, in and out of competition, under WADA Section S2 (WADA Prohibited List). Laboratories have published validated urine assays for it and its metabolites (Drug Test Anal 2015), and sanctions have followed in MLB and the UFC.

Does it build muscle or burn fat? No human trial has tested ipamorelin against a body-composition endpoint — the literature is animal work, one pharmacokinetic study, and one negative clinical trial. The nearest class evidence, two years of MK-677 in older adults, added about 1.1 kg of fat-free mass without improving strength or function (Ann Intern Med 2008).