The most selective growth hormone pulse
Injection · 503A Compounding
Educational content. This page describes Ipamorelin for informational purposes only and is not medical advice, diagnosis, or treatment. Consult a licensed provider before starting, stopping, or modifying any therapy.
Researched and maintained by the PepHookup team. Regulatory status last verified April 12, 2026.
Identified as the first growth hormone secretagogue to release GH with a specificity comparable to GHRH itself, sparing ACTH, cortisol, prolactin, and gonadotropins in preclinical work.[1]
In healthy men, a single dose produced one clean GH pulse peaking near 40 minutes with dose-proportional kinetics and a roughly 2-hour half-life, behaving as a tidy on/off stimulus rather than a sustained elevation. Dedicated pharmacokinetic characterization mapped its clearance and absorption profile across routes.[2][3]
Ghrelin-receptor secretagogues and GHRH act on complementary pathways. In humans, combining a GHRP with GHRH produces a markedly larger GH pulse than either alone, the rationale behind pairing ipamorelin with a GHRH analog such as CJC-1295.[4]
In a 117-patient Phase 2 trial, intravenous ipamorelin given twice daily for up to a week was generally well tolerated, with an adverse-event rate similar to placebo, though it did not improve the trial's efficacy endpoints.[8]
Ipamorelin is a synthetic pentapeptide (Aib-His-D-2-Nal-D-Phe-Lys-NH2, molecular formula C38H49N9O5, molecular weight about 712 g/mol) that acts as an agonist at the growth hormone secretagogue receptor (GHS-R1a), the same receptor targeted by the hormone ghrelin. It was developed at Novo Nordisk in the late 1990s and described by Raun and colleagues in 1998 as the first selective growth hormone secretagogue.
Its defining feature is selectivity. In the original characterization, ipamorelin released growth hormone with a potency similar to the earlier peptide GHRP-6 but, unlike GHRP-6, did not raise ACTH or cortisol even at high doses. This clean profile is why it is favored in research and clinical practice over older secretagogues that also drive cortisol and appetite.
Ipamorelin is not an FDA-approved drug for any indication. Its sequence contains non-proteinogenic amino acids, including aminoisobutyric acid (Aib) and a naphthylalanine residue (Nal), which the FDA has noted makes its impurity and aggregation behavior less well understood than that of standard peptides.
Ipamorelin binds GHS-R1a on the somatotroph cells of the anterior pituitary. The receptor couples through Gq/11 proteins to phospholipase C, generating IP3 and diacylglycerol and mobilizing intracellular calcium, which triggers the release of stored growth hormone in a discrete pulse rather than a continuous elevation.
Because it acts on the same receptor as ghrelin but with a refined binding profile, ipamorelin stimulates somatotrophs strongly while largely sparing the corticotrophs and lactotrophs that govern cortisol and prolactin. That receptor selectivity, demonstrated in pituitary and whole-animal studies, is the basis for its reputation as a clean GH stimulus.
Released growth hormone acts both directly and through hepatic IGF-1 to influence lipolysis, protein turnover, and tissue repair. Much of what is described for ipamorelin's downstream effects is inferred from growth hormone biology and animal data, since controlled human trials measuring body composition with ipamorelin have not been published.
The most selective growth hormone pulse
Ipamorelin is a selective GHS-R1a agonist on pituitary somatotrophs. Receptor activation drives Gq/PLC signaling, IP3 generation, and calcium influx that release a discrete pulse of growth hormone, while largely sparing the corticotroph and lactotroph pathways that raise cortisol and prolactin. Downstream GH and IGF-1 effects on lipolysis and tissue repair are inferred largely from GH biology and animal studies rather than human ipamorelin trials.
Ipamorelin released growth hormone with potency similar to GHRP-6 and a specificity comparable to GHRH, but did not increase ACTH or cortisol even at doses well above the GH-releasing threshold. This established its reputation as the first selective GH secretagogue.
Raun K, Hansen BS, Johansen NL, et al. · Eur J Endocrinol, 139(5):552-561 (1998) · PubMed
A single intravenous dose produced one GH pulse peaking near 0.67 hours with dose-proportional pharmacokinetics, clearance around 0.078 L/h/kg, and a terminal half-life of roughly 2 hours. No adverse events attributable to ipamorelin were reported. Note that this study used the intravenous route, not the subcutaneous route used in practice.
Gobburu JV, Agerso H, Jusko WJ, Ynddal L · Pharm Res, 16(9):1412-1416 (1999) · PubMed
Intravenous ipamorelin 0.03 mg/kg twice daily for up to 7 days was well tolerated, with adverse events comparable to placebo. It did not meet the primary endpoint: median time to a tolerated meal was 25.3 versus 32.6 hours (p = 0.15), and there were no significant differences in secondary efficacy measures.
Beck DE, Sweeney WB, McCarter MD; Ipamorelin 201 Study Group · Int J Colorectal Dis, 29(12):1527-1534 (2014) · PubMed
Subcutaneous ipamorelin produced dose-dependent increases in longitudinal bone growth and raised bone mineral content, and in a separate model partially counteracted glucocorticoid-induced suppression of bone formation. These effects have not been studied in humans.
Johansen PB, Nowak J, Skjaerbaek C, et al. · Growth Horm IGF Res, 9(2):106-113 (1999) · PubMed
start low, go slow
Subcutaneous (solo)
Subcutaneous (with a GHRH analog)
Subcutaneous (solo): Commonly dosed at bedtime on an empty stomach. Note that published human pharmacology used the intravenous route; subcutaneous dosing reflects clinical practice, not trial data.
Subcutaneous (with a GHRH analog): Paired to combine ghrelin-receptor and GHRH-receptor stimulation for a larger GH pulse than either alone.
Dosing is not standardized and should be determined by a licensed provider based on your goals, body weight, and clinical context. No subcutaneous regimen has been validated in a published human trial.
It is typically taken on an empty stomach, often at bedtime, because elevated blood glucose and recent food blunt the growth hormone response to secretagogues.
Practitioners often cycle secretagogues with periodic breaks on the theory that continuous stimulation can blunt the response, though this practice is based on clinical convention rather than controlled human data.
Human safety data are limited and short-term. The largest human exposure is the Phase 2 postoperative ileus trial, where intravenous ipamorelin was generally well tolerated over up to seven days but showed higher rates of hypokalemia and hyperglycemia than placebo.
In that trial, two ipamorelin-treated patients who had undergone bowel resection for colon cancer died of postoperative complications of anastomotic leak. The FDA has cited these deaths as a safety concern while also stating it is unclear whether they were related to ipamorelin.
Because secretagogues raise growth hormone and IGF-1, they carry the theoretical risks of growth hormone therapy, including effects on glucose metabolism. The FDA has separately flagged that ipamorelin's non-standard amino acids and the limited data on its impurities and aggregation leave its immunogenic potential uncharacterized.
Ipamorelin is not FDA-approved. Long-term human safety has not been established, and use should be supervised by a licensed provider with appropriate monitoring.
| Peptide | Primary Use | Administration | Cycle Length | Key Differentiator |
|---|---|---|---|---|
| Ipamorelin | GH stimulation for body composition and recovery | Subcutaneous injection (1-3x daily) | Determined by provider | The most selective GH secretagogue in preclinical work: a clean GH pulse without the cortisol, prolactin, or appetite effects of older GHRPs |
| SS-31 (Elamipretide) | Mitochondrial restoration and rare mitochondrial disease | Subcutaneous injection (daily); IV in trials | Ongoing daily dosing | The first FDA-approved mitochondria-targeted therapeutic; binds cardiolipin on the inner mitochondrial membrane to support electron transport efficiency |
| Semaglutide | Weight Management & Metabolic Health | Injection (weekly), Oral (daily) | Ongoing | The most clinically validated GLP-1 medicine, with outcomes data spanning weight, heart, kidney, and liver disease |
| Tirzepatide | Weight Loss & Type 2 Diabetes | Injection (weekly) | Ongoing | Only dual GIP/GLP-1 agonist; the deepest weight loss of any approved obesity drug, up to about 21% of body weight |
| Tesamorelin | Visceral Fat & GHRH Signaling | Subcutaneous Injection | Ongoing daily | The only FDA-approved GHRH analog, with Phase III data in over 800 patients, documented liver-fat reduction, and physiologic pulsatile GH release |
The FDA placed this substance in Category 2 of the 503A bulk drug substances evaluation, flagging significant safety risks. 503A compounding carries FDA enforcement risk, so most pharmacies decline to prepare it and many physicians hesitate to prescribe it.
Nomination withdrawn September 2024, then reviewed by PCAC on October 29, 2024. FDA cited unnatural amino acids, aggregation risks, and a literature report of death during IV administration for gastric motility. Remains ineligible for 503A compounding pending FDA final determination. Not among the 12 peptides HHS withdrew from Category 2 in April 2026.
PCAC reviewed ipamorelin for potential 503A inclusion
Removed from Category 2 (nomination withdrawn by nominators)
Placed in 503A Category 2 with significant safety risks identified
Last verified April 12, 2026. PepHookup tracks public FDA actions. This is not legal or medical advice.
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