Ipamorelin is the most selective growth hormone secretagogue ever characterized — and it is studied mostly as half of a combination stack.

The short version

Ipamorelin is a small lab-made peptide — five amino acids — that tells the pituitary gland to release a pulse of growth hormone (GH). Its claim to fame is being selective: it raises GH while barely touching two other hormones, cortisol (the stress hormone) and prolactin, that older peptides in its class pushed up. People in research-use communities are drawn to it for sleep, recovery, and slow changes in body composition, but those are reports, not proof. The honest state of the evidence is thin: one human trial that tested it (for slow bowel recovery after surgery) did not work, and there is no long-term human safety data. It has never been approved as a medicine anywhere. It is also banned in sport. Most online interest pairs it with another peptide, CJC-1295 — that pairing rests on each drug's separate pharmacology, not on any trial of the two together. What people report, including the downsides, is on the effects page.

What ipamorelin is

Ipamorelin (Aib-His-D-2-Nal-D-Phe-Lys-NH2; CAS 170851-70-4) is a synthetic pentapeptide — a chain of five amino acids — and a selective agonist of the ghrelin / growth hormone secretagogue receptor (GHS-R1a), the same receptor the natural "hunger hormone" ghrelin binds. To ask what is ipamorelin peptide is to ask about a molecule that Novo Nordisk derived in the 1990s from an earlier compound, GHRP-1, by removing a central dipeptide ^[1]. Two non-natural building blocks in its sequence — alpha-aminoisobutyric acid (Aib) and D-2-naphthylalanine — make it resist the enzymes that would otherwise chew it up.

What sets it apart from the peptides that came before it (GHRP-6, GHRP-2) is selectivity. In its founding characterization, ipamorelin released GH potently yet did not raise ACTH or cortisol above the level seen with growth-hormone-releasing hormone (GHRH) — even at doses more than 200-fold above the dose needed for half its maximal GH effect ^[1]. That clean profile is the entire reason it remains of interest decades later.

What the studies measured it doing

Asking what does ipamorelin peptide do has a precise answer in animals and a near-empty one in humans. In its founding swine work, the dose for half-maximal GH release was 2.3 nmol/kg, versus 3.9 nmol/kg for GHRP-6 — more potent, and far cleaner ^[1]. In adult female rats, 15 days of subcutaneous dosing raised the longitudinal bone-growth rate from 42 to as high as 52 micrometers per day, in a dose-dependent way, with no measurable change in circulating IGF-1 (insulin-like growth factor 1, a hormone made by the liver that carries out many of GH's effects) ^[4].

The single human pharmacology study found a terminal half-life of about 2 hours, with the GH response arriving as one discrete pulse that peaked roughly 40 minutes after dosing ^[2]. The most recent in-vivo work, a 2024 ferret study, found that ipamorelin blunted chemotherapy-induced weight loss by about 24% — through a peripheral, non-brain mechanism — while doing nothing for nausea ^[5]. These are real, cited results. None of them is a human outcome trial.

Where the 'safe' framing actually stands

The word in this site's name names a question, not a verdict. Ipamorelin's selectivity is a genuine relative-safety advantage: it spares the cortisol and prolactin elevations that dog less selective GHRPs ^[1]. But selectivity in one dimension is not a clean bill of health. The only controlled human trial of ipamorelin — a Phase 2 study in 114 bowel-resection patients — missed its primary endpoint, with no ipamorelin-specific safety signal across that short seven-day window but no demonstrated benefit either ^[3]. There is no Phase 3 trial, no approved indication, and no long-term human safety database of any kind.

There is also a class-level caution worth stating plainly: a 28-day study of a different GHS-R1a agonist found dose-dependent heart-muscle damage in rats ^[6]. Ipamorelin was not the compound tested, and no equivalent long-duration study of ipamorelin exists — which is precisely the point. The reported effects, the cautions, and the unknowns are laid out on the Ipamorelin effects page; the full study record is in the Ipamorelin research digest.

Why ipamorelin is almost always studied in a stack

Ipamorelin releases GH by a mechanism distinct from GHRH — it works on the ghrelin receptor, not the GHRH receptor — and the two pathways are complementary. A class-wide review documents that growth-hormone-releasing peptides act synergistically with GHRH and are partially resistant to the signals (glucose, free fatty acids, somatostatin) that nearly abolish a GHRH pulse on its own ^[7]. That pharmacology is the published rationale for pairing a GHRH analog with a GHRP.

The most discussed pairing in research-use communities is ipamorelin cjc-1295 — CJC-1295 being a long-acting GHRH analog. A separate comparison readers ask about is ipamorelin vs sermorelin, sermorelin being a short-acting GHRH analog. Both pages keep one line in view: the combination itself has never been tested in a trial for any outcome. The synergy is read off each agent's single-drug pharmacology.