What it is
Ipamorelin is a small lab-made chain of five amino acids, two of them unusual ones that the body does not use in its own proteins. It acts on the same switch as ghrelin, the “hunger hormone” made in the stomach, which also signals the pituitary gland to release growth hormone.
Earlier research compounds aimed at that switch also raised stress hormones such as cortisol. Ipamorelin attracted attention in the late 1990s because, in animal tests, it released growth hormone without that effect. It was later tested in hospital patients recovering from bowel surgery, where it did not perform better than placebo, and development stopped. It is not an approved medicine anywhere.
Ipamorelin (NNC 26-0161) is Aib-His-D-2-Nal-D-Phe-Lys-NH2 (C38H49N9O5, 711.9 g/mol), containing α-aminoisobutyric acid and D-2-naphthylalanine. It came from a series lacking the central Ala-Trp dipeptide of GHRP-1. It is an agonist at the growth hormone secretagogue receptor type 1a (GHS-R1a, the ghrelin receptor), a Gq-coupled receptor on pituitary somatotrophs and hypothalamic neurons; Raun et al. used GHRP and GHRH antagonists to show that it acts through the GHRP receptor rather than the GHRH receptor.
In primary rat pituitary cells the EC50 for GH release was 1.3 nmol/L (Emax 85% of GHRP-6). In conscious swine the ED50 was 2.3 nmol/kg; unlike GHRP-2 and GHRP-6 it did not raise ACTH or cortisol beyond GHRH-like levels, even at more than 200 times the GH ED50, and FSH, LH, prolactin and TSH were unaffected. In healthy men, intravenous pharmacokinetics were linear, with a terminal half-life of about 2 hours, clearance 0.078 L/h/kg and steady-state volume 0.22 L/kg.
Who made it and when
Ipamorelin was designed by scientists at Novo Nordisk in Denmark in the mid-1990s, as one result of a large chemistry program on growth hormone releasers. It was published in 1998 under the title “the first selective growth hormone secretagogue”. Novo Nordisk did not take it to market.
Its later clinical development was run by Helsinn Therapeutics, which tested an intravenous form in two mid-stage trials between 2008 and 2014 in people recovering from bowel surgery, on the theory that ghrelin-like drugs restart gut movement. The first trial missed its main goal and the second never published results. Development for that use was later reported as discontinued.
Raun et al. (Eur J Endocrinol 1998) described ipamorelin from Novo Nordisk’s GH-secretagogue chemistry programme; FDA’s 2024 briefing dates first synthesis to the mid-1990s and cites European patent EP 0736039 B1. Gobburu et al. (Pharm Res 1999) characterised human PK/PD in 48 healthy men.
Helsinn Therapeutics (U.S.) sponsored NCT00672074 (Phase 2, 117 enrolled, April 2008 to December 2009) and NCT01280344 (Phase 2 dose-finding, 320 enrolled, April 2011 to May 2014), both testing intravenous dosing for postoperative ileus after bowel resection. The first was published by Beck et al. in 2014; the second has no posted results and no publication could be found. A 2020 review cited in FDA’s briefing reports that development was discontinued after the disappointing results. FDA’s briefing also records outsourcing-facility reports of compounded ipamorelin injections from at least 2017 until about 2020, and marketing by medical spas and wellness clinics for uses such as weight loss and anti-ageing that were never studied in controlled trials.
What the data say
In rats and pigs, ipamorelin released growth hormone about as strongly as older compounds; in pigs it did so without raising cortisol or other pituitary hormones. In healthy men given it through a drip, it produced a single burst of growth hormone that peaked within an hour and faded within about six hours.
The main patient trial, in 114 people after bowel surgery, found that those given ipamorelin tolerated solid food a median of 25 hours after the first dose, against 33 hours on placebo, a difference that was not statistically reliable. Two people in the ipamorelin group died after surgical complications; whether the drug played any role is unknown. There are no controlled human data for injection under the skin.
Beck et al. 2014 (NCT00672074) randomised 117 patients; 114 formed the safety and modified intention-to-treat populations (ipamorelin 0.03 mg/kg IV twice daily, n=56; placebo, n=58). Median time to first tolerated standardised meal was 25.3 versus 32.6 hours (P = 0.15). There were no significant differences in secondary endpoints, including time to first bowel movement, GI-2 recovery and length of stay; a subgroup undergoing open laparotomy showed shorter recovery.
Treatment-emergent adverse events occurred in 87.5% versus 94.8%. Hypokalaemia (12.5% vs 3.4%), insomnia (10.7% vs 5.2%) and hyperglycaemia at discharge (14.3% vs 8.6%) were more frequent on ipamorelin; serious adverse events were 17.9% versus 15.5%. Two ipamorelin-treated patients with colon cancer died after anastomotic leak, from causes including sepsis and renal failure; FDA described the relationship as unclear.
Gobburu et al. 1999: GH peaked at about 0.67 hours (about 465 mIU/L) and returned to very low levels by 6 hours at all doses. FDA found no PK, PD or efficacy data for subcutaneous or other non-intravenous routes. An observational study registered in July 2026 (NCT07717866) lists ipamorelin within an endocrine “physiological supplementation” package given to special-operations veterans alongside ibogaine, 5-MeO-DMT and brain stimulation; it cannot isolate any effect of ipamorelin.
Regulatory picture
Approval: no ipamorelin medicine has been approved anywhere, and no active development program could be found.
Compounding: in September 2023 the FDA placed ipamorelin acetate in Category 2, its list of substances that raise significant safety concerns, for both ordinary compounding pharmacies (503A) and large outsourcing facilities (503B). For 503A pharmacies the nomination was withdrawn in 2024, and in October 2024 an FDA advisory committee voted 12 to 0, with one abstention, against adding ipamorelin to the list of ingredients they may compound with. It is not on that list. For 503B facilities it remains in Category 2.
Enforcement: in August 2026 the FDA issued a warning letter over a “research” tesamorelin-and-ipamorelin product. Sport: WADA prohibits ipamorelin at all times.
Approval: none. Neither ipamorelin free base nor the acetate is a component of any FDA-approved drug, and neither has a USP monograph.
Compounding: ipamorelin acetate was added to 503A and 503B Category 2 on 2023-09-29. The 503A listing was removed on 2024-09-27 after the nominations were withdrawn; FDA’s safety-risk page, updated 2026-04-22, still lists ipamorelin acetate in 503B Category 2 from 2023-09-29. FDA evaluated the free base and acetate on its own initiative for growth hormone deficiency (nominated) and postoperative ileus (added by FDA), at 2,000 mcg/mL for subcutaneous injection. It concluded that the criteria weighed against listing, citing no data for the subcutaneous route, the failed IV ileus trial, higher hypokalaemia and hyperglycaemia rates and two deaths, and the existence of approved therapies. On 2024-10-29 the committee voted 0–12 with 1 abstention on each salt form. Without a monograph, approved-drug component or 503A bulks listing, compounded products do not meet section 503A(b)(1)(A)(i). No final rule has been published, so the compounding field is recorded as unknown; the 503B Category 2 status is recorded above.
Sport: WADA 2026 S2.2.4 lists ipamorelin among growth hormone secretagogues.
