# Ipamorelin: The Evidence, Read Through the Gut and Appetite > Ipamorelin is a selective ghrelin-receptor agonist. A long-form, cited review of the gut-motility and appetite literature — what the studies support, and where they fall short. A long-form reading of the published record, led by the ghrelin-receptor lens: the founding selectivity data, the single failed human trial, and the open questions, every figure pinned to its study. ## Start here Ipamorelin is a small lab-made peptide — five amino acids long — that switches on the same receptor in the body as ghrelin, the hormone that makes you feel hungry. That receptor is called GHS-R1a (the ghrelin, or "growth hormone secretagogue," receptor). When ipamorelin flips that switch on the pituitary gland at the base of the brain, the gland releases a short burst of growth hormone. Its claim to fame is being *clean* about it: in animal studies it raised growth hormone without raising stress hormones like cortisol [1]. The same ghrelin switch also lives in the gut and the appetite centers of the brain, which is why this review reads ipamorelin through food, hunger, and gut movement. People in research-use communities mostly talk about deeper sleep, faster recovery, and sometimes more appetite — and what people report, including the downsides, is on [the effects page](/effects). One honest fact frames everything below: ipamorelin has never been approved as a medicine anywhere, and its only published human trial did not work [3]. ## The receptor is the whole story Ipamorelin (sequence Aib-His-D-2-Nal-D-Phe-Lys-NH2) is a synthetic pentapeptide — a chain of five amino acids built in a lab, not made by the human body. It is a selective agonist (a key that fits and turns one specific lock) at GHS-R1a, the ghrelin receptor. Ghrelin is the body's own "hunger hormone," and ipamorelin is described in the literature as a ghrelin mimetic: it copies ghrelin's action at that receptor [1]. What makes ipamorelin notable is restraint. In its 1998 founding characterization it released growth hormone (GH) potently in rat pituitary cells, anaesthetised rats, and conscious swine — with a swine ED50 of 2.3 nmol/kg, comparable to the older peptide GHRP-6 — yet it did **not** raise ACTH or cortisol above baseline even at doses more than 200-fold above its GH threshold [1]. That selectivity is its defining pharmacological feature and the reason it earned the label "the first selective growth hormone secretagogue" [1]. The ghrelin receptor is not only on the pituitary. It sits on enteric and vagal neurons that govern stomach emptying, and on the hypothalamic circuits that drive appetite. So a drug built to release GH inevitably touches the gut and hunger — the lens this review leads with. You can follow that thread on [Ipamorelin research](/research) and read the mechanism plainly on [what does ipamorelin peptide do](/how-it-works). ## The gut-motility rationale — promising on paper, thin in people Because ipamorelin activates the same receptor as ghrelin, it inherits ghrelin's prokinetic biology: high-dose ghrelin and synthetic ghrelin-receptor agonists stimulate gastric motility, increase gastric tone and emptying, and enhance the migrating motor complex — the gut's housekeeping wave between meals [10]. By 2009 the class was being tested in trials for gastroparesis and postoperative ileus [10]. Ipamorelin entered exactly that program. A mechanistic detail sharpens the gut connection. Radiolabel studies showed that GHRP-class peptides accumulate in the gastric glandular mucosa — the site where ghrelin is made — and that removing the stomach cut GHRP-6-induced GH release by 60–70% while leaving GHRH-induced release intact [8]. In other words, part of how these peptides work runs *through* the gut, by triggering the body's own ghrelin. That is why the appetite and motility lens is not a tangent here; it is close to the center of the molecule. The disappointment is human. The single published Phase 2 trial tested ipamorelin for postoperative ileus and missed its primary endpoint [3]. The story the literature tells is consistent: a strong receptor rationale, a clinically advanced drug class (relamorelin and other ghrelin agonists progressed further in GI development [7]), and ipamorelin itself stalling at proof-of-concept. ## What the human evidence actually is Human data on ipamorelin is sparse and largely negative for what it was tested on. The defining human anchor is a Phase 2 randomized controlled trial (NCT00672074) in 114 adults undergoing bowel resection, given 0.03 mg/kg intravenously twice daily for up to seven days [3]. Median time to first tolerated meal was 25.3 hours with ipamorelin versus 32.6 hours with placebo — a difference that did not reach statistical significance (p=0.15) [3]. Treatment-emergent adverse events occurred in 87.5% of the ipamorelin arm versus 94.8% of placebo, with no ipamorelin-specific safety signal in that short window [3]. The only other substantial human dataset is pharmacokinetic: a study in eight healthy male volunteers per dose level characterized a terminal half-life of about two hours, with a single growth-hormone pulse peaking around 40 minutes after dosing [2]. There are no completed Phase 3 trials and no approved indication anywhere [3]. Most contemporary use is off-label and self-administered by the subcutaneous route — a route with no published human safety or pharmacokinetic characterization at all. That is the honest shape of the file: rich preclinical pharmacology, one careful human PK study, one failed efficacy trial, and a large evidence gap where long-term human data would be. Recent reviews say the same — a 2026 sports-medicine review classed ipamorelin as investigational with no reproducible human evidence for musculoskeletal outcomes [16]. --- A long-form evidence review of the ipamorelin record read through its gut and appetite biology — the founding selectivity data weighed against the single failed human trial, and the word 'reviews' meaning only that the literature is appraised, never that a clinic, a vendor, or a prescription stands behind it.