Ipamorelin raised the bone-growth rate of rats dose-dependently — here is exactly what the skeletal studies measured.

Start here, in plain English

Ipamorelin is a lab-made peptide (a short chain of amino-acid building blocks) that tells the pituitary gland in the brain to release a pulse of growth hormone — the body's own signal for growth and repair. What makes it stand out is precision: it nudges growth hormone up without meaningfully raising stress hormones like cortisol, which older peptides in its family do ^[1]. Researchers were most curious about bone. In rats, ipamorelin made long bones grow faster, in step with the dose ^[4]. But the picture in people is thin: the only proper human trial — for slow bowel recovery after surgery — did not work ^[3]. So this site does two things at once: it celebrates what the bone and growth-hormone studies actually found, and it stays honest about how little has been tested in humans. What people report — including the downsides — is on the effects page, and the Ipamorelin research lays out every study.

What the skeletal studies actually showed

The headline finding sits in bone. When adult female rats received ipamorelin under the skin at 18, 90, and 450 micrograms a day for 15 days, the rate their long bones grew lengthwise climbed step by step with the dose — from 42 micrometers a day on placebo to 44, then 50, then 52 micrometers a day ^[4]. (A micrometer is one-thousandth of a millimeter; these are small, careful measurements of growth-plate activity, not visible changes.) What is striking is the route: blood levels of IGF-1 — the liver-made messenger that carries many growth-hormone effects — did not change ^[4]. That points to a partly local, pulse-driven skeletal effect rather than a flood of systemic growth factor.

A second study delivered ipamorelin continuously by a tiny implanted pump at 0.5 mg/kg per day for 12 weeks. It raised the mineral content of the tibia and spine, but the volumetric mineral density did not change ^[8]. Read carefully, that means the bones got bigger rather than denser. A third study tackled steroid-weakened bone: ipamorelin given alongside a glucocorticoid lifted the periosteal bone-formation rate roughly four-fold versus the steroid alone, and improved muscle force ^[7]. The skeletal signal is real and reproducible — but every datum here is from rodents, and that boundary matters.

The signature trait: selectivity

Ipamorelin's defining feature is what it does not do. In its founding 1998 characterization it released growth hormone potently in rat pituitary cells, anaesthetised rats, and conscious pigs (pig ED50 of 2.3 nmol/kg, close to GHRP-6's 3.9 nmol/kg), yet it did not push ACTH or cortisol above the level seen with the body's own releasing hormone — even at doses more than 200 times its growth-hormone threshold ^[1]. (ACTH and cortisol are the stress-hormone pair; older GH-releasing peptides such as GHRP-6 raise them.) That clean separation is why ipamorelin earned the label "the first selective growth hormone secretagogue," and why a study of the what is ipamorelin peptide chemistry keeps coming back to its receptor selectivity. It works through the ghrelin receptor (GHS-R1a), a different doorway than the GHRH analogs, which is the whole rationale for pairing it with one.

Where the human evidence stops

Human data on ipamorelin is sparse and, for the indication tested, negative. The single published Phase 2 randomized trial enrolled 114 adults recovering from bowel surgery and gave 0.03 mg/kg intravenously twice daily for up to seven days. It missed its primary endpoint: the median time to a first tolerated meal was 25.3 hours with ipamorelin versus 32.6 hours with placebo, which was not statistically significant (p=0.15) ^[3]. A separate human pharmacokinetic study in eight volunteers per dose established a terminal half-life of about two hours and a single growth-hormone pulse peaking near 40 minutes after a dose ^[2]. There are no completed Phase 3 trials and no approved indication anywhere ^[3]. The full record — including the dose-by-dose ipamorelin benefits reported in research and the cautions worth knowing — is laid out across this site, every figure tied back to its study in the Ipamorelin references.