Ipamorelin: Evidence, Mechanism, Dosing & Legal Status

Ipamorelin (NNC 26-0161; CAS 170851-70-4) is a synthetic pentapeptide growth-hormone secretagogue, historically described as "the first selective growth hormone secretagogue," and best known to consumers as the GHRP half of the CJC-1295 plus ipamorelin stack.1 Its mechanism is well documented; its marketed benefits are not. This monograph separates the two.

This article is informational and editorial content for research and educational purposes only. It is not medical advice, not a protocol to follow, and not a sourcing guide. Ipamorelin is not an FDA-approved drug; it is sold as a "research chemical not for human use" and is prohibited in sport. Dosing figures are reported strictly as seen in the published literature for completeness — not as recommendations. Consult a licensed clinician before any health decision.

What is ipamorelin and how does it work?

Ipamorelin is a synthetic pentapeptide, sequence Aib-His-D-2-Nal-D-Phe-Lys-NH2 (molecular formula C38H49N9O5, MW approximately 711.9 g/mol). It was engineered at Novo Nordisk from GHRP-1 by deleting the central Ala-Trp dipeptide, a change that preserved GH-releasing potency while sharply improving receptor selectivity; the D-amino acids and C-terminal amidation confer metabolic stability against peptidases.1 It acts as a selective agonist at the growth-hormone secretagogue receptor type 1a (GHS-R1a) — the ghrelin receptor — a Gq/11-coupled GPCR densely expressed on anterior-pituitary somatotrophs. Receptor activation drives phospholipase-C signaling to IP3/DAG and intracellular calcium mobilization, triggering exocytosis of GH-containing granules.1

The selectivity story is its defining feature. In pivotal swine and rat work, ipamorelin released GH with potency comparable to GHRP-6 (in-vitro rat-pituitary EC50 of 1.3 nmol/L; swine ED50 of 2.3 nmol/kg), but GHRP-6 and GHRP-2 both raised plasma ACTH and cortisol while ipamorelin did not — and that neutrality held even at doses more than 200-fold above the threshold for GH release. FSH, LH, prolactin and TSH were unaffected. The authors concluded ipamorelin is the first GHRP-receptor agonist with a selectivity for GH release similar to GHRH.1 That clean profile is exactly why ipamorelin became the preferred GHRP partner over GHRP-2 and GHRP-6.18 In the Phase-1 human study, ipamorelin showed dose-proportional kinetics with a terminal half-life of about 2 hours and a single GH pulse peaking near 40 minutes that declined to negligible GH by about 3 hours — preserving the pulsatile pattern of physiologic GH secretion rather than a flat, supraphysiologic elevation.2

What is the evidence by indication?

Ipamorelin has exactly one robust human pharmacodynamic finding and one human efficacy RCT, which was negative. Essentially every popularized therapeutic benefit is extrapolated from mechanism or animal data. The grades below separate these tiers explicitly.

The best-evidenced fact is mechanistic. In the Phase-1 dose-escalation study (8 healthy men per dose, single 15-minute IV infusions), ipamorelin reliably and dose-proportionally raised serum GH, producing a discrete pulse peaking around 40 minutes — a pharmacodynamic fact established in humans, but not proof of any downstream clinical benefit.2 The highest-quality human evidence is the multicenter, double-blind, placebo-controlled Phase-2 trial for postoperative ileus (the Ipamorelin 201 Study Group, registered as NCT00672074), in which roughly 114 adults undergoing bowel resection received IV ipamorelin 0.03 mg/kg twice daily versus placebo. Ipamorelin did not shorten time to first meal or improve colonic function versus placebo — the primary endpoint was not met, and development was discontinued for lack of efficacy.4 This negative trial paradoxically also serves as the principal human safety dataset.5

Everything else is preclinical or anecdotal. In rodents, ipamorelin increased body-weight gain and longitudinal bone growth, consistent with a GH/IGF-1 anabolic axis, but no human RCT demonstrates it improves body composition, reduces fat or builds muscle.1 Claims of accelerated recovery, tissue repair, anti-aging and better sleep have no controlled human trials and are biologically rationalized via GH/IGF-1 rather than demonstrated.6 A patent describes using ipamorelin to stimulate GI motility, but the human trial testing exactly that mechanism was negative.17

What about the CJC-1295 plus ipamorelin stack?

The most popular real-world use is not ipamorelin alone but the CJC-1295 (a GHRH analog) plus ipamorelin (a GHRP/ghrelin mimetic) stack. The rationale is two independent, complementary secretagogue pathways converging on the somatotroph: CJC-1295 drives the GHRH-R to Gas/cAMP/PKA cascade while ipamorelin drives the GHS-R1a to PLC/calcium cascade and dampens somatostatin tone — an "accelerator plus brake-release" that approximates the natural slow-wave-sleep GH surge.19 Classic endocrine studies show GHRH plus a GHRP-class peptide produce markedly greater pulsatile GH output than either alone, so the synergy principle is well established for the class.19

The crucial caveat: there are no published human RCTs of the specific CJC-1295-plus-ipamorelin combination as of 2026. The rationale is built from component pharmacology and analogous GHRH-plus-GHRP pairings, not a head-to-head combination trial.20 Ipamorelin is the preferred GHRP partner precisely because of its selectivity and low desensitization relative to GHRP-2 and GHRP-6.1 Both components are WADA-prohibited and neither is FDA-approved, so the stack's marketed outcomes (recovery, body composition, sleep, anti-aging) sit at Grade C/D.7

What doses appear in the literature?

Reported strictly as information, not a protocol. Because ipamorelin has no approved label, there is no authoritative human dose. The Phase-2 ileus trial used IV 0.03 mg/kg twice daily, and the Phase-1 study used single 15-minute IV infusions of 4.21 to 140.45 nmol/kg.42 Community and compounding reports commonly cite subcutaneous ~100 to 300 micrograms per dose, one to three times daily, often dosed pre-sleep or post-exercise to align with endogenous GH pulses, frequently combined with CJC-1295 — but these subcutaneous regimens have not been tested in any controlled trial, and no peer-reviewed subcutaneous PK/PD for ipamorelin exists.21 Because the GH pulse is short (peak ~40 minutes, gone by ~3 hours, half-life ~2 hours), multiple daily doses are used in practice to approximate physiologic pulsing.2

How safe is ipamorelin?

In the two published human trials ipamorelin was well tolerated: no clinically significant adverse events from single IV doses in healthy men, with vital signs, ECG and labs within normal limits, and good tolerability over up to 7 days of twice-daily IV dosing in surgical patients.24 Neither trial evaluated long-term or chronic subcutaneous use, so the safety of the way ipamorelin is actually used is unstudied.21 Commonly reported lower-quality and class-effect issues include injection-site reactions, headache, transient flushing, dizziness, fatigue, water retention, and — as a GH-class metabolic effect — possible transient hyperglycemia or reduced insulin sensitivity.18 The dominant theoretical concern is that any agent raising GH and IGF-1 could promote growth of pre-existing malignancy and stimulate cell proliferation; this is precautionary, not demonstrated. Precautionary contraindications include active or recent malignancy, pregnancy and lactation, pediatric use, and proliferative diabetic retinopathy. In practice the largest risk is often product quality: because no compounding pharmacy may legally prepare ipamorelin for human use under 503A as of 2026, products sold for research carry real risks of impurity, mislabeling, under- or over-dosing, and sterility failure.915

What is the FDA and WADA status in 2026?

Ipamorelin is not FDA-approved for any human indication; its clinical program ended after the negative Phase-2 ileus trial.4 The compounding timeline is precise. On September 29, 2023 the FDA moved roughly 17 to 19 popular peptides — explicitly including ipamorelin acetate — into 503A Category 2 of the interim bulk-substances list, citing significant safety risks; Category 2 effectively means do not compound.9 In late 2023 Evexias Medical Group and Farmakeio sued the FDA over the placement, and on September 27, 2024 the FDA removed five substances, including ipamorelin acetate, from Category 2 after the nominations were withdrawn.1011 The settlement required proper notice-and-rulemaking, including Pharmacy Compounding Advisory Committee review, before re-categorizing these APIs.10 As of mid-2026 a final rule is still pending, with the litigation administratively closed pending publication expected no later than March 14, 2027.11 The net effect: removed from the explicit Category-2 do-not-compound list, but not affirmatively placed on the permitted bulks list, so it remains not legally compoundable for human use under 503A, and any product sold sits outside the regulated pharmaceutical supply chain.14

For athletes the picture is unambiguous. Ipamorelin is prohibited by WADA at all times, in and out of competition, under S2.2.4 — growth-hormone-releasing factors, secretagogues and mimetics — grouped with anamorelin, capromorelin, ibutamoren (MK-677), macimorelin and ghrelin.7 WADA-accredited labs maintain detection methods for these growth-hormone-releasing factors, and any tested athlete risks a doping violation.8 Ipamorelin is a peptide and is not a controlled substance under the DEA schedules; its restriction runs through the FDA and the FD&C Act, not the Controlled Substances Act.6

Bottom line. Ipamorelin is a pharmacologically elegant, mechanistically validated GH secretagogue with essentially no proven clinical efficacy. It raises GH cleanly and selectively (Grade B), but its single human efficacy RCT failed (Grade A negative), and the celebrated recovery and recomposition benefits remain unproven (Grade C/D). It carries a meaningful regulatory and quality-risk profile: not FDA-approved, not legally compoundable under 503A as of mid-2026 with a final rule pending to roughly 2027, WADA-banned at all times, and sold only as unregulated research material. Regulatory facts here are current as of June 2026 and should be re-verified after the pending final rule publishes.1222