Ipamorelin

Ipamorelin is a pentapeptide with the sequence Aib-His-D-2-Nal-D-Phe-Lys-NH2. It came out of a Novo Nordisk chemistry programme that modified earlier growth hormone-releasing peptides (GHRPs), and was published in 1998 under the title “Ipamorelin, the first selective growth hormone secretagogue” ^[1].

It belongs to the same family as GHRP-2, GHRP-6 and hexarelin: small synthetic peptides that mimic ghrelin, the stomach hormone that stimulates GH release and appetite. What set ipamorelin apart in animal work was its selectivity. It is most often discussed alongside CJC-1295, a GHRH analogue that acts on a different pituitary receptor.

Chemically, ipamorelin was designed to be shorter and simpler than its predecessors. The Novo Nordisk team arrived at it by removing the central Ala-Trp pair from an earlier compound, GHRP-1, and then optimising the remaining structure. In anaesthetised rats it released GH with a potency and maximum effect comparable to GHRP-6, and in conscious pigs its effective dose for half-maximal GH release was about 2.3 nmol/kg, again similar to GHRP-6 ^[1]. It was therefore not more powerful than the older peptides; what distinguished it was what else it did, or rather did not do.

Ipamorelin activates the growth hormone secretagogue receptor (GHS-R1a). That receptor was cloned in 1996 as the target of synthetic GH secretagogues ^[2], and its natural ligand, ghrelin, was identified three years later ^[3]. Stimulating the receptor on the pituitary and hypothalamus triggers a pulse of GH release.

In the original pharmacology study, ipamorelin released GH from rat pituitary cells with potency and efficacy similar to GHRP-6, and its effect was blocked by GHRP antagonists but not GHRH antagonists, confirming it works through the GHRP receptor rather than the GHRH receptor ^[1]. In pigs, GHRP-6 and GHRP-2 raised ACTH and cortisol, but ipamorelin did not, even at doses more than 200 times higher than those needed for GH release; it also left FSH, LH, prolactin and TSH unchanged ^[1]. This selectivity is the reason ipamorelin is often described as a “cleaner” GHRP. It was shown in animals, not in controlled human comparisons.

Because the GHRH and ghrelin-receptor pathways are separate, combining the two classes gives a greater-than-additive GH response. This was shown in an early study in men given GHRP-6 together with GHRH ^[4]. It explains the popularity of pairing ipamorelin with CJC-1295 or sermorelin, though no published human trial has studied ipamorelin in combination with either.

Much of ipamorelin’s preclinical research was on bone. In adult female rats injected three times daily for 15 days (total doses of 18, 90 or 450 µg per day), ipamorelin increased the rate of longitudinal bone growth and body-weight gain in a dose-dependent way, without changing total IGF-1 or markers of bone turnover ^[5].

Over 12 weeks of continuous infusion in young adult female rats, both ipamorelin and GHRP-6 (0.5 mg/kg per day) increased bone mineral content. Further analysis showed this reflected larger bones rather than denser bone: volumetric bone mineral density did not change ^[6]. In rats given a high-dose glucocorticoid (methylprednisolone) for three months, adding ipamorelin at 100 µg/kg three times daily counteracted the steroid-induced fall in muscle strength and bone formation ^[7].

Ghrelin also speeds up the gut, and this became ipamorelin’s main clinical target. In rats that had undergone abdominal surgery with bowel handling, a model of post-operative ileus, single intravenous doses of ipamorelin (1 mg/kg) shortened the time to first bowel movement, and repeated dosing over two days increased stool output, food intake and weight gain ^[8]. A separate rat study found that ipamorelin accelerated gastric emptying after abdominal surgery: with a single intravenous dose of 0.014 µmol/kg, 52% of a test meal remained in the stomach after 15 minutes, compared with 78% in untreated operated rats and 44% in rats without surgery. In isolated stomach muscle, ipamorelin and ghrelin both restored contractions that surgery had suppressed, pointing to a ghrelin-receptor effect on the nerves that drive gut muscle ^[9]. These results led directly to the human ileus trial described below.

Apart from anti-doping studies of how it is metabolised, only two clinical studies of ipamorelin have been published. The first is a dose-escalation pharmacokinetic study in healthy men, with eight volunteers at each of five dose levels, who received 15-minute intravenous infusions. Ipamorelin had a short terminal half-life of about two hours, and each dose produced a single episode of GH release peaking at about 0.67 hours (40 minutes), then declining to negligible levels ^[10].

The second is a phase 2, multicentre, double-blind, placebo-controlled proof-of-concept trial in 117 adults undergoing bowel resection. Patients received intravenous ipamorelin or placebo twice daily for up to seven days after surgery. Ipamorelin was well tolerated, with treatment-emergent adverse events in 87.5% of the ipamorelin group and 94.8% of the placebo group, but it did not significantly shorten the time to tolerating a solid meal (median 25.3 hours versus 32.6 hours; p = 0.15), and secondary outcomes also showed no significant difference ^[11].

There are no published human trials of ipamorelin for body composition, muscle, fat loss, sleep, recovery or ageing. The claims made for those uses rest on its ability to raise GH in short-term studies and on the animal work above.

Ipamorelin is commonly discussed in combination with CJC-1295. The logic is pharmacological. Ipamorelin acts on the ghrelin receptor and CJC-1295 on the GHRH receptor, two separate inputs that the pituitary integrates. Human studies of older compounds showed that giving a GH-releasing peptide together with GHRH releases more GH than either alone, and more than their sum ^[4]. Pairing a selective ghrelin mimetic with a long-acting GHRH analogue is an extrapolation from that finding.

It is only an extrapolation. We found no published human study of ipamorelin combined with CJC-1295, whether the DAC version or the no-DAC version sold as Modified GRF (1-29), and no study of the combination’s effect on body composition, sleep or any other outcome. The doses circulated online for this combination do not come from clinical trials. Anyone comparing products should also be aware that “CJC-1295” can refer to two different molecules; our CJC-1295 guide explains the difference.

In healthy men, the pharmacokinetic study used intravenous infusions of 4.21, 14.02, 42.13, 84.27 and 140.45 nmol/kg over 15 minutes ^[10]. The post-operative ileus trial used 0.03 mg/kg intravenously twice daily for up to seven days ^[11]. Both were hospital-administered intravenous regimens, not the subcutaneous injections used by people self-administering the peptide.

Animal studies used, for example, 18 to 450 µg per day in rats ^[5], 0.5 mg/kg per day by infusion in rats ^[6], and 0.01 to 1 mg/kg intravenously in the rat ileus model ^[8]. These are animal doses and should not be converted to human doses. No subcutaneous human dose has been established in a published trial. For laboratory reconstitution arithmetic, see our peptide calculator.

In the phase 2 surgical trial, the overall rate of adverse events was similar to, and numerically lower than, placebo, in a population recovering from major surgery ^[11]. The pharmacokinetic study’s abstract does not report adverse events in detail ^[10]. Human safety data therefore come from short courses of intravenous dosing in hospital settings, with no long-term information and nothing on repeated subcutaneous use.

Ipamorelin’s reputation for not raising cortisol or prolactin comes from pig studies ^[1]; it has not been confirmed in a published head-to-head human study. As a ghrelin-receptor agonist it may be expected to increase appetite, as GHRP-2 does in people, but this has not been measured for ipamorelin in humans ^[15]. A 2026 clinical review of GH-axis peptides groups ipamorelin with other secretagogues whose reported adverse effects include hormonal and glucose changes, fluid retention, joint and muscle pain and injection-site reactions, and notes that the content of unregulated products is uncertain ^[12].

Ipamorelin is not an approved medicine in the UK, US, Canada, Australia or New Zealand. It is sold as a research chemical, and its legal position for buyers differs by country; see our legal status overview and the UK and US pages.

Ipamorelin is named on the WADA Prohibited List under S2 as a growth hormone secretagogue and is banned at all times ^[13]. Anti-doping laboratories have also identified glycine-extended versions of ipamorelin in black-market products ^[14].

Research-grade ipamorelin is supplied as freeze-dried powder. No stability data have been published for these products; general practice for lyophilised peptides is covered in our guide to storing peptides.

Ipamorelin is one of the most widely stocked research peptides. Compare prices, check the certificate of analysis with our guide on how to read a COA, and prefer third-party tested suppliers. Given the modified analogues found in seized products ^[14], a COA with a mass-spectrometry identity check is particularly useful.