Research digest
Ipamorelin: one ghrelin receptor, two jobs — gut motility and a clean growth-hormone pulse.
Swine GH ED50 of 2.3 nmol/kg. A ~2-hour human half-life. A single Phase 2 gut-motility trial that missed. Every number on this page is pinned to the study that measured it.
The short version
Ipamorelin is a small lab-made peptide — five amino acids strung together. It works by switching on the ghrelin receptor (the same receptor your body's natural "hunger hormone" uses), which sits both in the brain's hormone-control gland and in the nerves that run your gut. Flip that switch and two things happen in the research: the gland releases a short pulse of growth hormone, and the gut is nudged to move food along faster. Most of the careful evidence is in rats, swine, and ferrets. The one human trial that tested whether it speeds up a sluggish bowel after surgery did not beat placebo. Ipamorelin is not approved as a medicine anywhere. People in research-use communities report deeper sleep, faster recovery, and sometimes more hunger or a brief facial flush — but those are stories, not trials. What people report, including the downsides, is on the effects page.
What the ipamorelin literature actually measured
In its founding 1998 characterization, ipamorelin (sequence Aib-His-D-2-Nal-D-Phe-Lys-NH2) released growth hormone (GH — the body's main signal for tissue growth and repair) in rat pituitary cells, anaesthetised rats, and conscious swine, with a swine ED50 (the dose that produces half the maximum effect) of 2.3 nmol/kg versus 3.9 nmol/kg for GHRP-6 [1]. Its defining trait is selectivity: it triggered that GH pulse without raising ACTH or cortisol above the GHRH baseline, even at doses more than 200-fold above the GH ED50 [1].
The ghrelin receptor it activates — GHS-R1a — is not only in the pituitary. It sits on enteric and vagal neurons that drive gastric motility, which is why ipamorelin has a second, gut-side research story. In a surgical rat model of postoperative ileus (a stalled bowel after an operation), intravenous ipamorelin at 0.014 and 0.14 μmol/kg accelerated gastric emptying back toward non-operated control levels through a ghrelin-receptor/cholinergic-neuron mechanism [8]. A separate rat ileus study found repeated IV dosing increased fecal output, food intake, and body-weight gain over 48 hours [7].
Human data is thin and mostly negative. A population PK/PD study in healthy male volunteers fixed the terminal half-life at approximately 2 hours, with a single GH pulse peaking around 40 minutes after dosing [2]. The lone published Phase 2 trial — the one that put the gut-motility idea to a clinical test — did not clear placebo (details below).
The gut-motility lens: a ghrelin mimetic, by design
Ipamorelin is described in the literature as a ghrelin mimetic — a synthetic stand-in for the body's natural ghrelin. Ghrelin's prokinetic (gut-moving) actions are well reviewed: ghrelin-receptor agonists accelerate gastric emptying, raise gastric tone, and strengthen the migrating motor complexes that sweep the gut between meals [9][12]. That class-level biology is the reason ipamorelin was advanced toward a bowel-recovery indication rather than, say, a strength drug.
Class-mates make the case sharper. The ghrelin-receptor agonist TZP-101 reversed surgery- and opioid-induced gut-transit delay in rat models and decreased time to first bowel movement [13][14]. Newer ghrelin agonists such as relamorelin advanced further in GI-motility clinical development, situating ipamorelin inside a drug class with real prokinetic momentum [10]. The catch: momentum at the class level did not translate into a positive ipamorelin trial.
The appetite signal — and why it cuts both ways
Because ipamorelin works through the ghrelin receptor, an appetite effect is built into its mechanism. Ghrelin is the "hunger hormone," and ghrelin-receptor agonists activate the brain's feeding centers as a class. In community reports, some users describe a noticeable uptick in hunger in the hours after a dose — milder than older peptides like GHRP-6, but real enough to matter for anyone watching their intake.
That same biology is being explored for the opposite problem: involuntary weight loss. In a 2024 ferret study, intraperitoneal ipamorelin (1-3 mg/kg) reduced chemotherapy-induced body-weight loss by roughly 24% on the last day of the delayed phase — though it had no anti-emetic effect [5]. The appetite question gets its own page: does ipamorelin make you hungry.
Status, in plain terms
Ipamorelin is not FDA-approved for any use. It was discovered by Novo Nordisk in the 1990s, characterized in 1998 [1], taken into a single Phase 2 trial for postoperative ileus that missed its primary endpoint [3], and never marketed. In 2024 the FDA removed ipamorelin acetate from Category 2 of the interim Section 503A bulk-substances list and reviewed it at the October 29, 2024 Pharmacy Compounding Advisory Committee meeting, tightening compounding-pharmacy access. It is prohibited in sport at all times under the WADA Prohibited List (category S2). This site is editorial: it documents that record. It is not a clinic and it does not sell anything. For how the molecule works, read the Ipamorelin research; for community-reported effects and cited cautions, read the Ipamorelin effects.