Ipamorelin: what the scientific research shows

By the Ipamorelin Research editorial team · Last reviewed November 11, 2026 · Scientific review: pending

What ipamorelin is

Ipamorelin is a synthetic pentapeptide with the sequence Aib-His-D-2-Nal-D-Phe-Lys-NH₂, developed at Novo Nordisk under the code NNC 26-0161 and first described in 1998 [Raun 1998]. Three of its five residues are not standard L-amino acids, and the C-terminus is an amide rather than a free acid[PubChem]. It is a growth hormone secretagogue: it binds the growth hormone secretagogue receptor GHSR-1a, the receptor that the body's own hormone ghrelin uses, and causes the pituitary to release growth hormone.

What made it notable was selectivity. In conscious swine, the comparison compounds GHRP-6 and GHRP-2 raised the stress hormones ACTH and cortisol, while ipamorelin did not raise them significantly even at doses more than 200-fold above the dose needed for growth hormone release, and left FSH, LH, prolactin and TSH unchanged[Raun 1998]. The authors called it the first GHRP-receptor agonist with growth hormone selectivity comparable to GHRH. Nearly every description of ipamorelin written since traces back to that one experiment.

How it works, step by step

The pathway below is built only from relationships that an indexed study supports, and each step says what kind of support that is and in which species it was measured. Steps marked in amber rest on related compounds or indirect evidence; the final step is marked in red because it is where the chain stops.

The full explanation, including a text version of every step, is on the mechanism of action page.

The human evidence, in full

There are 2 registered clinical trials of ipamorelin. Both are phase 2, both are complete, and between them they randomised 437 people. Results exist in the public record for 117 of them.

• NCT00672074, published in 2014: 117 patients, ipamorelin 0.03 mg/kg intravenously twice daily against placebo after bowel resection. Median time to first tolerated meal was 25.3 hours against 32.6 hours for placebo, which did not reach statistical significance (P = 0.15). The authors reported no significant differences in the key and secondary efficacy analyses [Beck 2014].
• NCT01280344: 320 patients across four arms at 45 sites, completed May 2014. No results posted, no publication found [NCT01280344].
• A 1999 dose-escalation study in 40 healthy men measured the pharmacokinetics and the growth hormone response: a half-life of about two hours and a single pulse of growth hormone peaking at 0.67 hours and declining to negligible levels at every dose [Gobburu 1999].

The human evidence page sets out each trial in full, including the adverse events as the publication and FDA each described them.

What the animal research actually found

Several findings in the preclinical literature point in a different direction from the claims commonly made about this compound, and they were reported by the researchers themselves.

• Body fat went up, not down. In growth-hormone-deficient and growth-hormone-intact mice, ipamorelin increased fat pad weights relative to body weight, increased relative body fat measured by DEXA, and increased food intake and serum leptin. Growth hormone itself decreased fat mass in the same experiment. The authors concluded secretagogues increase body fat through mechanisms that bypass growth hormone [Lall 2001].
• Growth hormone rising does not mean IGF-1 rising. In adult female rats, 15 days of ipamorelin raised tibial growth rate dose-dependently while total IGF-1, IGF binding proteins and bone turnover markers were all unchanged [Johansen 1999]. In diabetic mice, ipamorelin produced higher growth hormone than in healthy mice while IGF-1 did not rise at all, because the liver was resistant[Johansen 2003].

The claims page takes each commonly stated benefit and sets it against what was measured, in what species.

What is sold is not always what was studied

Two independent analytical studies found that material sold as these peptides carried an extra glycine residue at the N-terminus. A 2018 study of black-market growth-promoting products identified Gly-Ipamorelin and confirmed it by custom synthesis [Krug 2018], and a 2019 analysis of preparations seized by Danish customs identified glycine-extended analogues of ipamorelin, GHRP-2, GHRP-6 and modified GRF (1-29)[Gajda 2019]. This is a finding about product identity, separate from anything about the compound itself, and it means research findings cannot be assumed to apply to purchased material.

Verified molecular data

Every value comes from the PubChem record for CID 9831659 [PubChem]. PubChem holds no three-dimensional conformer for this compound, so this site shows the verified 2D structure and does not display a rotating model. The molecular data page has the interactive structure, the full identity record and the measured pharmacokinetics.

Regulatory position

Ipamorelin is not an approved drug: a Drugs@FDA query by generic and substance name returns no match[openFDA]. FDA added ipamorelin acetate to its Category 2 list of bulk substances that may present significant safety risks in compounding on 29 September 2023, citing immunogenicity risk from aggregation or peptide-related impurities and the complexity introduced by unnatural amino acids[FDA Category 2]. On 29 October 2024 the Pharmacy Compounding Advisory Committee voted 0 in favour and 12 against, with 1 abstention, on adding each of ipamorelin acetate and ipamorelin free base to the 503A Bulks List, recording a lack of information supporting safety and efficacy in the available data[PCAC minutes].

Research questions

Most recently published records

The corpus was assembled from a PubMed search for ipamorelin and NNC 26-0161, which returned 55 records, all of which are indexed here [PubMed search]. Reviews are kept separate from primary research and never counted as evidence; of the 55 records, 13 are reviews or commentary, and a 2020 review of this compound class states in its own conclusions that clinical efficacy data largely remain lacking [Sinha 2020].