Peptides & growth hormone

Ipamorelin

Updated · 22 sources · Editorial policy

Ipamorelin (development code NNC 26-0161) is a small synthetic peptide that makes the pituitary gland release a pulse of growth hormone (GH). Like GHRP-2, GHRP-6 and hexarelin, it activates the ghrelin receptor. Novo Nordisk scientists described it in 1998 as “the first selective growth hormone secretagogue,” because in pigs it released GH without raising the stress hormones ACTH and cortisol, unlike the older GH-releasing peptides (Raun et al., Eur J Endocrinol 1998).

The most important fact: ipamorelin has never been approved as a medicine anywhere we could find. The only patient trials we found tested it for postoperative ileus (slow return of bowel function after surgery), and the one published phase 2 trial showed no significant benefit over placebo. No study has tested it for muscle, fat loss, recovery or performance in people. FDA lists it as a significant safety risk for compounding by outsourcing facilities, and WADA bans it at all times.

This page summarizes what the published studies and regulators report. It is for education only and is not medical advice.

Property Detail
Class Synthetic pentapeptide growth hormone secretagogue; ghrelin receptor agonist
Other names NNC 26-0161; ipamorelin acetate (salt named by FDA)
Structure Five-amino-acid peptide amide, C38H49N9O5, molecular weight 711.9 (PubChem)
Approval None found; not an FDA-approved drug
Routes studied in humans Intravenous (pharmacokinetic study and ileus trials); intranasal (single-volunteer anti-doping study)
Doses in cited human studies 4.21–140.45 nmol/kg IV over 15 minutes (single doses); 0.03 mg/kg IV twice daily for up to 7 days (ileus trial)
Half-life ≈2 h terminal half-life after IV infusion in healthy men
Key feature In pigs, released GH without raising ACTH, cortisol, prolactin, LH, FSH or TSH
FDA compounding Category 2 (significant safety risks) for outsourcing facilities (503B) since September 29, 2023
US controlled substance Not a scheduled controlled substance
WADA status Prohibited at all times (S2.2.4, named among growth hormone secretagogues)

What it is

Ipamorelin came out of a Novo Nordisk chemistry program that tried to shrink the earlier GH-releasing peptides. The team started from GHRP-1 and removed its two central amino acids, leaving a five-amino-acid peptide (Raun et al., 1998). Like the older GHRPs it contains unnatural building blocks: an N-terminal aminoisobutyric acid and two D-amino acids (mirror-image forms that resist breakdown by enzymes), one of them a naphthyl-substituted alanine (PubChem CID 9831659). It is one amino acid shorter than GHRP-2, GHRP-6 and hexarelin, which are hexapeptides.

The history of the GHRP family, the cloning of the ghrelin receptor and the discovery of ghrelin are covered on the GHRP-6 and GHRP-2 pages. Novo Nordisk later used ipamorelin as the starting point for smaller, more orally available compounds (Ankersen et al., J Med Chem 1998). Helsinn later sponsored the postoperative ileus trials of ipamorelin itself (ClinicalTrials.gov NCT00672074; NCT01280344).

What “selective” means here

In its first pharmacology paper, ipamorelin was compared head-to-head with GHRP-6 and GHRP-2 (Raun et al., 1998):

Measure Ipamorelin GHRP-6 GHRP-2
GH release, rat pituitary cells (EC50; max effect) 1.3 nmol/L; 85% 2.2 nmol/L; 100% Not stated
GH release in conscious pigs (ED50) 2.3 nmol/kg 3.9 nmol/kg 0.6 nmol/kg
Peak GH in pigs (Emax) 65 ng/mL 74 ng/mL 56 ng/mL
ACTH and cortisol in pigs Not raised beyond the GHRH comparison, even at over 200 times the ED50 Raised Raised
FSH, LH, prolactin, TSH in pigs Not affected Not affected Not affected

So ipamorelin was about as potent as GHRP-6, less potent than GHRP-2 by dose, and the only one of the three that did not raise ACTH and cortisol. The authors described its selectivity as similar to that of GHRH (growth hormone-releasing hormone, the body’s own GH-releasing signal).

This selectivity was shown in pigs. The published human pharmacokinetic study reported GH responses only (Gobburu et al., Pharm Res 1999), and we found no published human study that measured cortisol, ACTH or prolactin after ipamorelin. A 2026 clinical review nonetheless groups ipamorelin as largely sparing these axes, in contrast to GHRP-2, GHRP-6 and hexarelin (Dominikowski et al., Front Endocrinol 2026).

Pharmacokinetics

The only published human pharmacokinetic study used a dose-escalation design: five IV infusion rates from 4.21 to 140.45 nmol/kg over 15 minutes, with eight healthy men at each dose level (Gobburu et al., Pharm Res 1999):

Parameter Value
Dose proportionality Pharmacokinetics were dose-proportional
Terminal half-life 2 h
Clearance 0.078 L/h per kg
Volume of distribution (steady state) 0.22 L/kg
GH response A single episode of GH release at all doses, peaking at 0.67 h (≈40 min), then falling to negligible levels
Concentration for half-maximal GH stimulation 214 nmol/L

The 2 h half-life is longer than the ≈33 minutes reported for GHRP-2 in children (GHRP-2 page), although the studies used different populations and were not head-to-head. Even so, each dose produced one GH pulse that returned to baseline, not a sustained rise. This is the main difference from oral ibutamoren (MK-677), which acts on the same receptor but is taken by mouth once daily and raised IGF-1 over weeks of use in trials.

Animal and excretion data add a few details:

  • In rats, ipamorelin’s plasma clearance was about 5 times lower than GHRP-6’s. It was mainly excreted in urine, whereas GHRP-6 went mainly into bile, and 60–80% of the dose was recovered intact. Nasal bioavailability was about 20%, lower than the ≈50% seen for GHRP-2 (Johansen et al., Xenobiotica 1998).
  • In one human volunteer given a nasal dose, ipamorelin was broken down extensively. A four-amino-acid fragment was still detectable in urine after the parent peptide had disappeared (Semenistaya et al., Drug Test Anal 2015).

We found no published human data for subcutaneous injection, which is how ipamorelin is typically used outside trials. FDA likewise states that it has not identified safety information for those other injectable routes (FDA Category 2 list).

Regulatory status

  • Approval. We found no approval of ipamorelin as a medicine in the US or elsewhere.
  • FDA compounding. FDA placed ipamorelin acetate in Category 2 for outsourcing facilities (section 503B) on September 29, 2023. FDA cites a risk of immune reactions (immunogenicity) from peptide aggregation or impurities, the added difficulty of characterizing a peptide with unnatural amino acids, and “serious adverse events including death” in a published study of IV ipamorelin for gastric motility. It also states that it lacks information to judge harm by other injectable routes. FDA also lists ipamorelin acetate among substances whose nominations were withdrawn by the nominators, while noting it remains in Category 2 under the 503B policy (FDA Category 2 list, current as of April 22, 2026).
  • Controlled substances. Ipamorelin is not a steroid and is not named in the DEA schedules, including the Schedule III list of anabolic steroids (21 CFR 1308.13).
  • Sport. WADA names ipamorelin among the growth hormone secretagogues under S2.2.4, prohibited in and out of competition (WADA 2026 Prohibited List).

What the research shows

The human evidence for ipamorelin consists of one pharmacokinetic study in healthy men and one published phase 2 trial in surgical patients. Everything about bone, muscle and body composition comes from rats and mice.

Postoperative ileus (human trials)

Ghrelin-receptor agonists speed up gut movement, so Helsinn tested ipamorelin as a treatment for ileus after bowel surgery. In rats with surgically induced ileus, IV ipamorelin shortened the time to the first bowel movement, and repeated dosing increased stool output, food intake and weight gain over 48 hours (Venkova et al., J Pharmacol Exp Ther 2009). It also sped up gastric emptying in the same rat model (Greenwood-Van Meerveld et al., J Exp Pharmacol 2012).

The human trial did not confirm a benefit. This multicenter, double-blind, placebo-controlled phase 2 study enrolled 117 adults having small or large bowel resection, of whom 114 were analyzed (Beck et al., Int J Colorectal Dis 2014):

Outcome Ipamorelin 0.03 mg/kg IV twice daily Placebo
Median time to first tolerated solid meal 25.3 h 32.6 h (p = 0.15, not significant)
Any treatment-emergent adverse event 87.5% 94.8%
Secondary efficacy outcomes No significant differences —

Treatment ran from the first day after surgery for up to 7 days or until discharge. The authors noted the study was small and enrolled patients with a wide range of underlying conditions.

A second, larger phase 2 trial (320 patients, three IV dose regimens vs placebo) was registered and listed as completed in 2014, but no results are posted on ClinicalTrials.gov and we found no publication (ClinicalTrials.gov NCT01280344).

Bone, muscle and body composition (animal studies only)

These results are from rodents and have not been tested in people:

Study Animals and dosing Main finding
Johansen et al., Growth Horm IGF Res 1999 Adult female rats, subcutaneous 18, 90 or 450 µg/day for 15 days Dose-dependent faster bone lengthening (42 to 44, 50 and 52 µm/day) and weight gain; no change in IGF-1
Svensson et al., J Endocrinol 2000 Young adult female rats, continuous infusion 0.5 mg/kg/day for 12 weeks Higher bone mineral content from bigger bones; bone density per volume unchanged
Andersen et al., Growth Horm IGF Res 2001 Adult female rats on a glucocorticoid (methylprednisolone), 100 µg/kg three times daily for 3 months Counteracted the steroid-induced loss of calf muscle strength; 4-fold higher periosteal bone formation than steroid alone
Aagaard et al., Growth Horm IGF Res 2009 Rats on prednisolone, 0.5 mg/kg/day for 7 days Reduced steroid-induced protein (nitrogen) wasting, but less effectively than GH at the doses given
Lall et al., Biochem Biophys Res Commun 2001 Mice, twice-daily injections for up to 9 weeks Increased body fat relative to body weight, even in GH-deficient mice; raised food intake and leptin

The mouse study is a reminder that ghrelin-receptor agonists can increase appetite and fat independently of GH. GHRP-2 raised food intake in controlled human studies (see the GHRP-2 page), but we found no human data on ipamorelin and appetite.

About “the clean, side-effect-free GH peptide.” Ipamorelin is often marketed as the selective, gentle option among GH-releasing peptides, and is commonly paired with CJC-1295 without DAC. The evidence is thinner than the claim. Its selectivity for GH over cortisol and prolactin was shown in pigs; we found no published human hormone panel beyond GH. It has never been tested for muscle, fat loss or recovery in people, and a 2026 clinical review describes the CJC-1295 pairing as driven largely by anecdote, with limited controlled evidence for synergy or body-composition benefit (Dominikowski et al., 2026). Its one efficacy trial in humans was negative.

Side effects and risks

Human safety data come from short IV use only: single doses in healthy men and up to 7 days in hospitalized surgical patients. There are no long-term human safety data.

What the trials reported

In the ileus trial, ipamorelin was described as well tolerated, with treatment-emergent adverse events in 87.5% of patients on ipamorelin and 94.8% on placebo (Beck et al., 2014). These rates reflect recovery from major bowel surgery more than the drug itself. The published abstract does not break down serious adverse events. FDA’s compounding review, however, refers to serious adverse events including death in a published study of IV ipamorelin for gastric motility, without stating that ipamorelin caused them (FDA Category 2 list).

FDA’s concerns for injected products

FDA’s reasons for listing ipamorelin acetate as a significant compounding risk are (FDA Category 2 list):

  • possible immune reactions from peptide aggregation or peptide-related impurities;
  • unnatural amino acids that make the peptide harder to characterize and quality-control;
  • the serious adverse events noted above;
  • no safety information for the subcutaneous and other injectable routes used outside trials.

Long-term GH and IGF-1 exposure

Because ipamorelin’s purpose is to raise GH, the known risks of raised GH and IGF-1 are plausible but have not been studied for ipamorelin itself. For a drug acting on the same receptor, longer trials of ibutamoren (MK-677) found rises in blood sugar, fluid retention and a heart failure signal in frail older patients. See also growth hormone. The 2026 review notes that cancer concerns tied to IGF-1 are theoretical, with no direct evidence of cancer in clinical studies of these peptides (Dominikowski et al., 2026).

Who was studied

Only adults have received ipamorelin in published human studies. There are no data in pregnancy, breastfeeding, children, or people with diabetes, cancer or heart disease.

Quality and contamination

Ipamorelin sold online is not a regulated product, so dose, purity, sterility and identity are not guaranteed. Anti-doping and forensic laboratories have found modified versions on the black market:

  • German and Norwegian anti-doping labs identified a glycine-extended form of ipamorelin (an extra amino acid on one end) in black-market products, alongside similar variants of GHRP-2 and GHRP-6 (Krug et al., Growth Horm IGF Res 2018).
  • Powders seized by Danish customs contained the same kind of glycine-modified analogs of ipamorelin, GHRP-2, GHRP-6 and modified GRF 1-29 (Gajda et al., Drug Test Anal 2019).

These modified peptides have never been tested for safety or effect. At least one anti-doping lab added ipamorelin and its main urinary metabolite to its routine screening method (Semenistaya et al., 2015).

Key takeaways

  • A selective ghrelin-receptor agonist, in pigs. Ipamorelin is a five-amino-acid peptide that releases a GH pulse. In pigs it did not raise ACTH or cortisol, unlike GHRP-2 and GHRP-6, but this has not been shown in published human hormone studies.
  • Never approved. Its only clinical program was for postoperative ileus. The published phase 2 trial in 117 patients found no significant benefit, and a larger trial was never published.
  • Short-acting. IV ipamorelin had a ≈2 h half-life in healthy men, and each dose produced a single GH peak at about 40 minutes.
  • No human data for muscle or body composition. Bone, muscle and fat effects come from rat and mouse studies only.
  • Regulators flag it. FDA lists ipamorelin acetate as a significant compounding safety risk for outsourcing facilities, and WADA bans it at all times. Black-market products have contained modified, untested analogs.

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. PubMed.
  2. Ankersen M, Johansen NL, Madsen K, et al. A new series of highly potent growth hormone-releasing peptides derived from ipamorelin. J Med Chem. 1998;41(19):3699–3704. PubMed.
  3. 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. PubMed.
  4. Johansen PB, Hansen KT, Andersen JV, Johansen NL. Pharmacokinetic evaluation of ipamorelin and other peptidyl growth hormone secretagogues with emphasis on nasal absorption. Xenobiotica. 1998;28(11):1083–1092. PubMed.
  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. PubMed.
  6. Helsinn Therapeutics (U.S.), Inc. Safety and efficacy of ipamorelin for management of post-operative ileus. NCT00672074. ClinicalTrials.gov.
  7. Helsinn Therapeutics (U.S.), Inc. Safety and efficacy of ipamorelin compared to placebo for the recovery of gastrointestinal function. NCT01280344. ClinicalTrials.gov.
  8. Venkova K, Mann W, Nelson R, Greenwood-Van Meerveld B. Efficacy of ipamorelin, a novel ghrelin mimetic, in a rodent model of postoperative ileus. J Pharmacol Exp Ther. 2009;329(3):1110–1116. PubMed.
  9. Greenwood-Van Meerveld B, Tyler K, Mohammadi E, Pietra C. Efficacy of ipamorelin, a ghrelin mimetic, on gastric dysmotility in a rodent model of postoperative ileus. J Exp Pharmacol. 2012;4:149–155. PubMed.
  10. 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. PubMed.
  11. 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. PubMed.
  12. Andersen NB, Malmlöf K, Johansen PB, et al. The growth hormone secretagogue ipamorelin counteracts glucocorticoid-induced decrease in bone formation of adult rats. Growth Horm IGF Res. 2001;11(5):266–272. PubMed.
  13. Aagaard NK, Grøfte T, Greisen J, et al. Growth hormone and growth hormone secretagogue effects on nitrogen balance and urea synthesis in steroid treated rats. Growth Horm IGF Res. 2009;19(5):426–431. PubMed.
  14. Lall S, Tung LY, Ohlsson C, et al. Growth hormone (GH)-independent stimulation of adiposity by GH secretagogues. Biochem Biophys Res Commun. 2001;280(1):132–138. PubMed.
  15. Semenistaya E, Zvereva I, Thomas A, et al. Determination of growth hormone releasing peptides metabolites in human urine after nasal administration of GHRP-1, GHRP-2, GHRP-6, Hexarelin, and Ipamorelin. Drug Test Anal. 2015;7(10):919–925. PubMed.
  16. Krug O, Thomas A, Malerød-Fjeld H, et al. Analysis of new growth promoting black market products. Growth Horm IGF Res. 2018;41:1–6. PubMed.
  17. Gajda PM, Holm NB, Hoej LJ, et al. Glycine-modified growth hormone secretagogues identified in seized doping material. Drug Test Anal. 2019;11(2):350–354. PubMed.
  18. Dominikowski A, Rękoś Z, Olejarz M, et al. The emerging landscape of performance-enhancing peptides modulating GH-IGF1 axis: bridging the gap between clinical evidence and patient self-administration. Front Endocrinol (Lausanne). 2026;17:1822475. PubMed.
  19. Food and Drug Administration. Certain bulk drug substances for use in compounding that may present significant safety risks (Category 2). Content current as of April 22, 2026. FDA.
  20. Code of Federal Regulations. 21 CFR 1308.13, Schedule III. 21 CFR 1308.13.
  21. World Anti-Doping Agency. The 2026 Prohibited List, in effect January 1, 2026. WADA 2026 Prohibited List.
  22. National Center for Biotechnology Information. Ipamorelin, PubChem CID 9831659. PubChem.