Ipamorelin raised rat bone growth rate from 42 to 52 microm/day, and it does it without a cortisol spike.

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Ipamorelin is a small lab-made peptide — a chain of five amino acids — that tells the brain's hormone gland to release a short burst of growth hormone (the body's natural growth and repair signal). It copies the action of ghrelin, the same "hunger hormone" that normally triggers that release. What makes ipamorelin stand out is that it does this cleanly: it raises growth hormone without raising the stress hormone cortisol, which older peptides in its family could not avoid.

Most of the evidence comes from rats and a handful of pigs, with one small human pharmacology study and a single human trial that did not work for the condition it tested. Scientists have measured faster bone growth, a clean hormone pulse, and changes in body composition in animals. People in research-use communities most often report deeper sleep and faster recovery — but those reports are anecdotal, not proven, and the honest downsides, including a class-level heart-safety question, are laid out on the effects page.

The skeletal numbers, first

The cleanest bone result is a dose-response. Subcutaneous ipamorelin at 18, 90 and 450 microg/day (split three times daily for 15 days) lifted the longitudinal bone growth rate of adult female rats from 42 microm/day on vehicle to 44, 50 and 52 microm/day — and it did so with no measurable change in total IGF-1 (insulin-like growth factor 1, the liver-made messenger that carries many growth-hormone effects) or bone-turnover markers ^[2]. The skeletal effect tracked the dose even when the systemic growth-factor reading stayed flat, which points to a partly local, pulse-driven mechanism.

Longer exposure shifts the readout. Ipamorelin 0.5 mg/kg/day delivered continuously by osmotic minipump for 12 weeks raised total tibial and vertebral bone mineral content on DXA scans in young female rats, while cortical volumetric bone mineral density was unchanged ^[3] — bone got bigger, not denser. And against a steroid headwind, ipamorelin 100 microg/kg three times daily for 3 months raised the periosteal bone formation rate roughly four-fold versus glucocorticoid alone in older female rats ^[4]. The signal is reproducible across labs. It is also entirely preclinical — these are rat skeletons, measured carefully, not human outcomes.

Why the hormone pulse is clean

Ipamorelin's defining property is selectivity. In its founding 1998 characterization it released growth hormone potently in rat pituitary cells, anaesthetised rats and conscious swine — swine ED50 of 2.3 nmol/kg versus 3.9 nmol/kg for GHRP-6 — yet it did not raise ACTH or cortisol above the level seen with growth-hormone-releasing hormone, even at doses more than 200-fold above its growth-hormone ED50 ^[1]. That made it the first highly growth-hormone-selective secretagogue (a "secretagogue" is simply a compound that makes a gland secrete a hormone).

The mechanism is receptor-level. Ipamorelin switches on GHS-R1a, the ghrelin receptor, on the pituitary's growth-hormone-producing cells, opening a calcium signal that fires a hormone pulse ^[1]. Because that route is separate from the GHRH (growth-hormone-releasing hormone) pathway, the two stack — which is the entire rationale behind pairing ipamorelin with a GHRH analog like CJC-1295, covered in the Ipamorelin research.

What the human data actually says

Human evidence is thin and largely negative. The pharmacology was mapped in 1999: across single IV infusions of 4.21 to 140.45 nmol/kg in healthy men, kinetics were dose-proportional, terminal half-life landed near 2 hours, and the growth-hormone response came as a single discrete pulse peaking about 40 minutes after dosing ^[6]. That is the cleanest human dataset that exists.

The only published Phase 2 trial (NCT00672074, 114 bowel-resection patients, 0.03 mg/kg IV twice daily for up to 7 days) was built to speed gut recovery after surgery and missed its primary endpoint — time to first tolerated meal was 25.3 h on ipamorelin versus 32.6 h on placebo, p=0.15 ^[7]. No ipamorelin-specific safety signal surfaced in that short window, but efficacy was not shown, and no Phase 3 followed. Ipamorelin has never been approved as a drug anywhere.

How to read this site

This is an editorial digest, not a clinic and not a store. The numbers above are study figures, attributed to the papers that measured them; none of it is a dosing instruction, and the literature is dominated by animal work. The Ipamorelin effects page is the honest human-interest layer — what the research-use community reports, clearly labeled anecdotal, plus the cited safety cautions. For the molecule itself, the what is ipamorelin peptide primer breaks down the structure and naming, and the dose-graded ipamorelin benefits page gathers the bone and body-composition findings in one place. Every quantitative claim on this site maps to a numbered source in the Ipamorelin references.