Ipamorelin clears the body in roughly two hours and fires a single growth-hormone pulse at the forty-minute mark.

The short version

Ipamorelin is a small lab-made peptide — a chain of five amino acids — that tells the pituitary gland (a pea-sized gland under the brain) to release a burst of growth hormone. What makes it stand out is its precision: in animal studies it raised growth hormone without raising the stress hormone cortisol or the hormone prolactin, which the older peptides in its class did ^[1]. The numbers that matter most are about timing. In the one human study, the peptide left the bloodstream with a half-life (the time for the level in blood to drop by half) of about 2 hours, and the growth-hormone burst it set off peaked roughly 40 minutes after the dose ^[2]. People in research-use communities report deeper sleep and faster recovery; they also report flushing, hunger, and water retention. What people report — including the downsides — is on the effects page. One important fact up front: ipamorelin has never been approved as a medicine anywhere, and the single mid-stage human trial it reached did not work ^[3].

What the ipamorelin record actually measures

Ipamorelin is a synthetic pentapeptide (Aib-His-D-2-Nal-D-Phe-Lys-NH2) and a selective agonist of the ghrelin receptor — formally the growth hormone secretagogue receptor type 1a, or GHS-R1a (the docking site on pituitary cells that the hunger hormone ghrelin normally fits). Activating it triggers a pulse of growth hormone. The founding 1998 characterization measured that pulse and, more importantly, measured what it did not trigger: in conscious swine ipamorelin released growth hormone with an 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 the growth-hormone ED50 ^[1]. That selectivity — power without the off-target hormones — is the entire reason the molecule was named the first selective growth hormone secretagogue.

The pharmacokinetics are where this site leads, because they are unusually well pinned for a research peptide. Human pharmacokinetic-pharmacodynamic modeling in eight healthy male volunteers per dose level, given five 15-minute intravenous infusions ranging from 4.21 to 140.45 nmol/kg, found dose-proportional kinetics: a terminal half-life of approximately 2 hours, a clearance of 0.078 L/h/kg, and a steady-state volume of distribution of 0.22 L/kg ^[2]. The growth-hormone response was a single discrete pulse peaking at about 0.67 hours — 40 minutes — after dosing ^[2]. Read the half-life page for the full elimination profile.

One human trial, and it missed

The defining human anchor is a single Phase 2 randomized controlled trial. Under registration NCT00672074, 114 adults undergoing bowel resection received 0.03 mg/kg of ipamorelin intravenously twice daily for up to seven days ^[3]. The trial missed its primary endpoint: 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 the placebo arm — no ipamorelin-specific safety signal surfaced in that short window, but efficacy was not demonstrated ^[3]. No Phase 3 trial followed, and no regulator has ever approved the compound ^[3].

The contrast between that thin human record and the broad preclinical literature is the honest frame for everything here. Across rodent and large-animal models the selective growth-hormone effect is reproducible; the human outcome data is one negative trial and one pharmacokinetic dataset. This is a research story, not a verdict — but the verdict so far, where verdicts exist, is that efficacy in humans was not shown.

What the preclinical models added

Beyond the founding characterization, the animal literature filled in mechanism and body-composition signals. Subcutaneous ipamorelin at 18, 90, and 450 microg/day (divided three times daily for 15 days) raised the longitudinal bone-growth rate of adult female rats from 42 microm/day on vehicle to 44, 50, and 52 microm/day, with no measurable change in total IGF-1 or bone-turnover markers — a partly local, pulse-driven skeletal effect ^[4]. The most recent published in-vivo study, a 2024 ferret experiment, found that intraperitoneal ipamorelin (1-3 mg/kg) inhibited cisplatin-induced body-weight loss by roughly 24% during the delayed phase, while having no anti-emetic effect ^[5].

The metabolism literature is equally specific. In male rats, ipamorelin showed roughly five-fold lower plasma clearance than GHRP-6, with 60-80% of the dose recovered intact in bile and urine and an intranasal bioavailability near 20% ^[7]. The receptor reach extends past the pituitary, too: ex vivo pancreatic tissue from normal and diabetic rats released insulin directly in response to ipamorelin, a peripheral effect independent of growth hormone ^[13]. These are the Ipamorelin research details that the pharmacokinetics lens is built on — the clearance numbers, the route comparisons, and the single human dataset that ties them together.

How to read this site

This is a research digest, not a clinic and not a store. The word 'doctor' in the domain names a reading posture — examining the evidence closely — not a medical service, and nothing here is medical advice. Three habits run through every page. First, leading with the measurement: the half-life, the clearance, the ED50, the trial endpoint, before any interpretation. Second, keeping community reports separate from clinical findings — anecdotal effects people describe are labeled as such and never carry a dose. Third, citing every quantitative claim to a primary source, listed in full on the references page. The result is a frank account of what the ipamorelin literature shows: a precisely characterized pharmacokinetic profile, a reproducible selective mechanism, one negative human trial, and a long-term human safety record that simply does not yet exist ^[2][3].

The pages are organized around that pharmacokinetics-first frame. The two dedicated pages answer the timing questions people ask most: how long does ipamorelin stay in your system, which walks through the half-life, clearance, and volume of distribution, and how long does it take for ipamorelin to work, which separates the roughly 40-minute hormonal onset from the multi-week effects users report. The research page lays out the full mechanism and every key study; the dosage page reports only the doses that appear in published work, never a recommendation. For the honest human-interest layer — what people say they feel, good and bad, plus who has reason to be careful — start with the effects page.