What it is
Ipamorelin is made in a lab. It is a short chain of five amino acids (a peptide). Two of those amino acids are unusual. The body does not use them in its own proteins.
Ipamorelin works on the same switch as ghrelin. Ghrelin is the “hunger hormone” made in the stomach. It also tells the pituitary gland (a small gland at the base of the brain) to release growth hormone.
Older lab compounds that hit this switch also raised stress hormones, such as cortisol. In the late 1990s, animal tests showed ipamorelin released growth hormone without doing that. This made it stand out. Later it was tested in hospital patients healing from bowel surgery. It did not work better than a dummy treatment (placebo). Work on it then 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
Scientists at Novo Nordisk in Denmark made ipamorelin in the mid-1990s. It came out of a large project to make drugs that release growth hormone. It was published in 1998. The paper called it “the first selective growth hormone secretagogue” (a drug that makes the body release growth hormone). Novo Nordisk never sold it.
Later, a company called Helsinn Therapeutics tested it. They gave it into a vein. They ran two mid-stage trials between 2008 and 2014. The people in them were healing from bowel surgery. The idea was that ghrelin-like drugs might help the gut start moving again. The first trial did not reach its main goal. The second trial never shared its results. Work on this use was later reported as stopped.
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 not raise cortisol or other hormones from the pituitary gland. Healthy men were given it through a drip into a vein. It caused one burst of growth hormone. The level peaked within an hour. It faded within about six hours.
The main patient trial had 114 people after bowel surgery. People on ipamorelin could eat solid food 25 hours after the first dose. This is the median (the middle value). On placebo it took 33 hours. This gap was too small to be sure it was real. Two people on ipamorelin died after problems from their surgery. No one knows if the drug played any part. There are no controlled human studies of it given as a shot 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. We could not find any company still working on one.
Compounding (pharmacies mixing their own versions): in September 2023, the FDA put ipamorelin acetate in Category 2. This is its list of substances with serious safety concerns. It covered both regular compounding pharmacies (503A) and large outsourcing facilities (503B).
For 503A pharmacies, the request to allow it was withdrawn in 2024. In October 2024, an FDA expert panel voted 12 to 0 against letting these pharmacies use it. One member did not take a side. It is not on their allowed list. For 503B facilities, it is still in Category 2. Ipamorelin was not among the six peptides in the US health department’s October 2026 draft policy easing enforcement.
Enforcement: in August 2026, the FDA sent a warning letter about a product sold “for research”. It mixed tesamorelin and ipamorelin.
Sport: WADA (the World Anti-Doping Agency) bans 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. Ipamorelin is not among the six peptides covered by the HHS draft enforcement-discretion policy of 2026-10-30.
Sport: WADA 2026 S2.2.4 lists ipamorelin among growth hormone secretagogues.
