# Ipamorelin: A Pharmacokinetics-First Reading of the Selective GH Secretagogue

> Ipamorelin clears with a terminal half-life of about 2 hours and fires a single GH pulse peaking near 40 minutes. The selectivity, the kinetics, and the open questions, cited to source.

A pharmacokinetics-first digest of the most selective growth hormone secretagogue ever characterized — the half-life, the clearance, the selectivity, and the open questions, every number cited to its study.

## Start here

Ipamorelin is a tiny lab-made peptide — five amino acids long — that tells the brain's growth-hormone switch to flip on for a moment. It does that by hitting the same receptor as ghrelin, the body's natural "hunger and growth" signal. What makes it interesting is how *clean* it is: it raises growth hormone (the body's repair-and-build hormone) without dragging up the stress hormone cortisol or other unwanted signals, which the older peptides in its family always did. In healthy volunteers it left the body fast — about a two-hour half-life — and pushed up one short pulse of growth hormone that peaked around forty minutes after dosing. People in research-use communities mostly talk about deeper sleep and faster recovery; the honest catch is that the one real human trial (for slow bowels after surgery) did not work, and there is no long-term safety data. What people report — including the downsides — is on [the effects page](/effects). Ipamorelin is not an approved medicine anywhere.

## The kinetics are the story: about two hours, one clean pulse

In healthy male volunteers, Ipamorelin behaved like a textbook well-behaved drug. Across five single intravenous doses spanning 4.21 to 140.45 nmol/kg, its kinetics were dose-proportional — double the dose, roughly double the exposure — with a terminal half-life (the time for blood levels to fall by half during clearance) of about 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 (GH) response was not a smear; it was a single discrete pulse peaking at roughly 0.67 hours — about 40 minutes — after dosing [2]. That tight, predictable pulse is the whole pharmacological appeal: a brief, clean GH signal that mimics the body's own pulsatile rhythm rather than a flat, sustained elevation. In male rats, plasma clearance ran roughly 5-fold lower than the older peptide GHRP-6, with 60-80% of the dose recovered intact in bile and urine and an intranasal bioavailability near 20% [10]. The full curve lives on [how long does ipamorelin stay in your system](/half-life).

## Selectivity is what set it apart from everything before it

When Ipamorelin (sequence Aib-His-D-2-Nal-D-Phe-Lys-NH2) was first characterized, it released GH potently — comparably to GHRP-6, with a swine ED50 of 2.3 nmol/kg versus 3.9 nmol/kg for GHRP-6 — yet it did not raise ACTH or cortisol above baseline even at doses more than 200-fold above its GH ED50 [1]. That single result made it the first highly GH-selective growth hormone secretagogue. The mechanism: it activates the ghrelin / growth hormone secretagogue receptor (GHS-R1a — the docking site on pituitary cells that ghrelin normally uses) and triggers a calcium-driven GH release, without the off-target adrenal and prolactin stimulation that dogged GHRP-6 and GHRP-2 [1]. Because it works through a pathway distinct from growth-hormone-releasing hormone (GHRH), it became the natural partner for GHRH analogs — the basis of the well-known CJC-1295 pairing. The mechanism diagram and the synergy data are on the [Ipamorelin research](/research) page.

## What three decades of studies actually measured

The animal record is consistent on a narrow set of outcomes. Subcutaneous Ipamorelin at 18, 90, and 450 micrograms/day (divided three times daily for 15 days) raised the longitudinal bone-growth rate of adult female rats from 42 to 44, 50, and 52 micrometers/day in a clean dose-response, and it did so with no measurable change in total IGF-1 or bone-turnover markers — pointing to a partly local, GH-pulse-driven skeletal effect rather than a systemic IGF-1 surge [4]. The most recent published in-vivo study, a 2024 ferret model, found intraperitoneal Ipamorelin (1-3 mg/kg) cut chemotherapy-induced body-weight loss by about 24% in the delayed phase, though it produced no anti-emetic effect [5]. Where the data turns sobering is in humans: the only published Phase 2 randomized trial, in 114 bowel-resection patients, missed its primary endpoint — time to first tolerated meal was 25.3 hours on Ipamorelin versus 32.6 hours on placebo (p=0.15) [3]. The benefits people report, and the cautions worth knowing, are laid out on [Ipamorelin effects](/effects).

## Status, in plain terms

Ipamorelin has never been approved as a drug by any regulatory authority. Novo Nordisk discovered it in the 1990s; it was later developed for postoperative ileus, reached Phase 2, missed the endpoint, and went no further [3]. It is prohibited in sport at all times under the World Anti-Doping Agency's category S2, and accredited laboratories can detect it and its metabolites in urine [11]. 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. This site sells nothing and recommends nothing — the word "source" in the name refers to source *literature*. It is a reading of the published record, and the full citation list is on [Ipamorelin references](/references).

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A pharmacokinetics-first reading of the Ipamorelin record — the two-hour half-life and the single forty-minute GH pulse logged before anything else, the failed human trial kept in plain view, and the community reports fenced off as unverified; no clinic wired behind the console and nothing here sourced, dosed, prescribed, or sold.