Ipamorelin: Research Overview

Ipamorelin is a synthetic pentapeptide growth hormone secretagogue (GHS) developed by Novo Nordisk in the late 1990s. It was the first GHS demonstrated to be highly selective for growth hormone release, stimulating GH secretion without meaningful elevations in cortisol, ACTH, prolactin, or other pituitary hormones — a selectivity profile that distinguished it from earlier GHRPs such as GHRP-2 and hexarelin. Though it never advanced beyond phase 2 clinical trials, ipamorelin generated a detailed human pharmacokinetic dataset and became a widely referenced benchmark for the GHS compound class. It remains classified as a research chemical and is not approved for human therapeutic use by any major regulatory body.

What is Ipamorelin?

Ipamorelin (Aib-His-D-2-Nal-D-Phe-Lys-NH2) is a five-residue amidated peptide with a molecular weight of approximately 711.85 Da. It belongs to the growth hormone secretagogue class, acting as an agonist at the growth hormone secretagogue receptor (GHSR), also known as the ghrelin receptor. Unlike natural ghrelin or some synthetic GHRPs, ipamorelin’s pentapeptide structure confers a relatively clean receptor-binding profile, activating GHSR with high potency while producing minimal off-target stimulation of other pituitary hormone axes. Ipamorelin is sold by research-chemical vendors as a lyophilized powder, typically in 2 mg, 5 mg, or 10 mg vials, and is not approved by the FDA or any major regulatory body for clinical use.

Mechanism of Action

Ipamorelin binds the growth hormone secretagogue receptor 1a (GHSR-1a), a G-protein-coupled receptor expressed on somatotroph cells of the anterior pituitary. Receptor activation increases intracellular calcium via phospholipase C (PLC) and IP3 signaling, triggering GH secretion. This pathway is distinct from — and synergistic with — the GHRH/cAMP pathway activated by CJC-1295 and sermorelin, which is why the two compound classes are frequently combined in research settings.

The selectivity of ipamorelin is its defining pharmacological feature. Raun et al. (1998, PMID 9849822) showed in swine that doses producing substantial GH release did not elevate ACTH, cortisol, prolactin, LH, FSH, or TSH — a profile markedly superior to GHRP-6, which stimulates prolactin and cortisol at equivalent GH-releasing doses. This selectivity is attributed to ipamorelin’s inability to activate the ERK pathway through GHSR at the doses required for GH release, limiting spillover activation of other hypothalamic-pituitary axes.

What the Research Shows

The foundational selectivity data appear in the Raun et al. 1998 preclinical characterization (PMID 9849822), which established ipamorelin’s potent and selective GH-releasing profile in vitro and in vivo. Hansen et al. (1999, PMID 10496658) then conducted the human pharmacokinetic-pharmacodynamic modeling study in healthy volunteers, establishing dose-proportional PK, a terminal half-life of approximately 2 hours, and a GH release peak at roughly 40 minutes post-injection.

The most advanced clinical data for ipamorelin come from a phase 2 randomized controlled trial in patients recovering from bowel resection surgery, evaluating its potential to accelerate recovery of gastrointestinal motility (postoperative ileus). Popescu et al. (2014, PMID 25331030) reported that ipamorelin administered by intravenous infusion twice daily for up to 7 days was well tolerated. This represents the only published phase 2 data and used an IV route rather than the subcutaneous route studied in healthy volunteers. No phase 3 efficacy trial for any indication has been published for ipamorelin.

Pharmacokinetics

Based on the Hansen et al. 1999 human PK/PD study (PMID 10496658), ipamorelin displays dose-proportional pharmacokinetics following subcutaneous administration. Key parameters include: terminal half-life approximately 2 hours, clearance of approximately 0.078 L/h/kg, and volume of distribution at steady state of approximately 0.22 L/kg. GH secretion peaks at approximately 40 minutes (0.67 h) following SC injection and declines rapidly thereafter, consistent with the short half-life. The peptide is thought to be cleared primarily by enzymatic degradation; no active metabolites have been identified.

Common Research Dose Ranges

Not medical advice. These are ranges reported in research literature, not personalized recommendations. Consult your physician.

Literature from the human PK/PD study (Hansen et al., 1999; PMID 10496658) and the phase 2 postoperative ileus trial (Popescu et al., 2014; PMID 25331030) reports dose ranges of approximately 30–100 mcg. The phase 2 trial used intravenous infusion twice daily; the pharmacokinetic study used single subcutaneous doses. Literature reports intravenous infusion twice daily in the postoperative ileus trial and single subcutaneous doses in pharmacokinetic studies.

Storage

Lyophilized ipamorelin should be stored at −20 °C in a dry environment. Once reconstituted with bacteriostatic water, the solution should be kept at 2–8 °C and used within 14 days. Ipamorelin is a small peptide that is moderately sensitive to degradation; reconstituted solutions should not be left at room temperature for extended periods.

What Ipamorelin Is NOT

Ipamorelin is often grouped with other growth hormone-releasing peptides (GHRPs) such as GHRP-2, GHRP-6, and hexarelin, but these are distinct compounds with different receptor selectivity profiles. GHRP-6 and GHRP-2 are known to stimulate cortisol and prolactin release at GH-effective doses; ipamorelin does not. Ipamorelin also acts via a different receptor pathway than CJC-1295 or sermorelin, which are GHRH analogs targeting the GHRHR rather than GHSR. Finally, ipamorelin is not ghrelin: while both are GHSR agonists, ghrelin is a 28-amino-acid acylated peptide with additional metabolic functions mediated through peripheral GHSR expression, whereas ipamorelin’s pharmacology is focused on pituitary GH release.

References

Citations for this guide are listed below. All PubMed links resolve to the NCBI abstract page for the referenced article.