Peptide Briefs

Ipamorelin

Evidence grade: B — reviewed September 2026 Published controlled human trials: 1 (negative) · Published human PK studies: 1 · Unpublished registered trials: 1 · Animal studies: ~15 Also known as: NNC 26-0161, Ipamorelin acetate Sequence: Aib-His-D-2-Nal-D-Phe-Lys-NH₂ (5 amino acids) · MW ≈ 711.9 Da

Ipamorelin is one of the few compounds on Peptide Briefs with a real pharmaceutical history: it was designed at Novo Nordisk, characterized in a 1998 paper as the first selective growth-hormone secretagogue, dosed in healthy volunteers in a published pharmacokinetic study, and taken into a randomized, placebo-controlled Phase 2 trial by Helsinn Therapeutics. That is why it grades B. The trial was for post-surgical gut motility, not muscle or recovery, and it failed: ipamorelin did not beat placebo on any endpoint, a larger follow-up study was never published, and the program was dropped. Nothing about ipamorelin’s popular reputation — lean mass, recovery, sleep, “clean” GH release — has been tested in a published human trial.

What ipamorelin is

Ipamorelin is a pentapeptide that binds the ghrelin receptor (GHS-R1a) in the pituitary and triggers a pulse of the body’s own growth hormone. Earlier GH-releasing peptides (GHRP-2, GHRP-6, hexarelin) do the same thing but also raise cortisol, ACTH, and prolactin. Ipamorelin was engineered to release GH without those side effects, which is what “selective” means in the 1998 paper’s title and why the compound became popular in gray-market stacks, usually paired with a GHRH analog such as CJC-1295 or sermorelin.

What the studies looked at

Discovery and selectivity (1998). Raun et al., working at Novo Nordisk, showed in rats and pigs that ipamorelin released GH with potency similar to GHRP-6 but without the ACTH or cortisol rise seen with other secretagogues. This is the paper every vendor cites; it is an animal and in-vitro study.

Bone and growth (1999–2000). Johansen et al. reported that ipamorelin induced longitudinal bone growth in rats; Svensson et al. found it increased bone mineral content in adult female rats. Both are the origin of the “bone density” claims.

Human pharmacokinetics (1999). Gobburu et al. gave 15-minute intravenous infusions to healthy male volunteers across five dose levels and modeled the GH response. Kinetics were linear and dose-proportional. This remains the only published human PK study. It established that ipamorelin does release GH in people; it says nothing about outcomes.

Postoperative ileus, Phase 2 (2014). Beck et al. (Ipamorelin 201 Study Group) ran a prospective, randomized, double-blind, placebo-controlled proof-of-concept trial in 117 patients after bowel resection, testing whether intravenous ipamorelin would speed recovery of gut motility. It did not separate from placebo on the primary endpoint or any secondary endpoint. A 320-patient dose-finding study (NCT01280344) completed in 2014 and never posted results. Helsinn discontinued development.

Later preclinical work. Scattered rodent studies since 2015 have examined ipamorelin in gut motility, visceral pain, and cachexia models; none has been followed by a human trial.

What the evidence does not show

  • No published human trial of ipamorelin for body composition, muscle, recovery, sleep, bone density, or aging — the uses it is sold for.
  • No published human data on subcutaneous administration; the only human studies used intravenous infusion.
  • No long-term human safety data; total published human exposure is a few dozen volunteers and roughly 60 trial patients over days, not months.
  • No human study of ipamorelin combined with CJC-1295 or any GHRH analog, despite that being the most common way it is discussed.
  • The one controlled human trial that exists was negative.

Regulatory and sport status

  • FDA (US): Never approved. In 2023 the FDA placed ipamorelin in Category 2 of its bulk drug substances list for compounding, citing insufficient safety data.
  • WADA: Prohibited in sport under section S2 (growth hormone secretagogues).
  • Legal supply: Sold in the US only as a research-use-only chemical.

Stability, storage, and handling in the laboratory

Lyophilized ipamorelin is stable at −20 °C for extended periods and tolerates brief room-temperature exposure in shipping. The non-natural residues (Aib, D-2-Nal, D-Phe) make it more resistant to enzymatic breakdown than a natural pentapeptide would be. Reconstituted in bacteriostatic water, laboratory practice is 2–8 °C and use within a few weeks. Identity by mass spectrometry should show a parent mass near 712 Da.

Common questions

Is ipamorelin “clinically proven”? It was clinically tested — once, for post-surgical gut recovery — and it failed. It has never been clinically tested for anything it’s popular for.

Why does it grade B if the trial was negative? Because Peptide Briefs grades the amount and quality of evidence, not the direction of the result. A properly controlled human trial exists. That’s more than most compounds on this site can say, and a negative result is still information.

Isn’t it safer than the older GHRPs? In animals it releases less cortisol and prolactin. In humans, the only data are short infusions in volunteers and surgical patients, where it was tolerated. “Safer” over months of use has not been studied.

Could the grade change? It would move to A with a second controlled human trial, whatever the outcome. It stays B until then.

Sources

  1. Raun K, Hansen BS, Johansen NL, et al. Ipamorelin, the first selective growth hormone secretagogue. Eur J Endocrinol. 1998;139(5):552–561. PMID 9849822.
  2. Johansen PB, Nowak J, Skjaerbaek C, et al. Ipamorelin, a new growth-hormone-releasing peptide, induces longitudinal bone growth in rats. Growth Horm IGF Res. 1999;9(2):106–113. PMID 10373343.
  3. Svensson J, Lall S, Dickson SL, et al. The GH secretagogues ipamorelin and GH-releasing peptide-6 increase bone mineral content in adult female rats. J Endocrinol. 2000;165(3):569–577. PMID 10852480.
  4. Gobburu JV, Agersø H, Jusko WJ, Ynddal L. Pharmacokinetic-pharmacodynamic modeling of ipamorelin, a growth hormone releasing peptide, in human volunteers. Pharm Res. 1999;16(9):1412–1416. PMID 10496658.
  5. Beck DE, Sweeney WB, McCarter MD; Ipamorelin 201 Study Group. Prospective, randomized, controlled, proof-of-concept study of the ghrelin mimetic ipamorelin for the management of postoperative ileus in bowel resection patients. Int J Colorectal Dis. 2014;29(12):1527–1534. PMID 25331030.
  6. Helsinn Therapeutics. Ipamorelin dose-finding study in postoperative ileus. ClinicalTrials.gov NCT01280344 (completed 2014; no results posted).
  7. US FDA. Certain Bulk Drug Substances for Use in Compounding That May Present Significant Safety Risks. 2023.
  8. WADA Prohibited List 2026, section S2.

Peptide Briefs is an independent reference published by the founders of Agape Compounds LLC. Nothing on this page is medical advice or a recommendation to use any compound outside a research setting. Grade reviewed September 2026.