Ipamorelin is the peptide that taught one receptor to fire cleanly: growth hormone, released — cortisol and prolactin, left quiet.

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Ipamorelin is a small lab-made peptide — a chain of five amino acids — built to do one thing well: tell the pituitary gland (a pea-sized gland at the base of the brain) to release a pulse of growth hormone. It does this by switching on the ghrelin receptor (the same docking point your body's natural hunger hormone uses). What made it notable in 1998 is what it does not do. Older peptides in its family also spiked stress hormones — cortisol and prolactin. Ipamorelin raised growth hormone strongly while leaving those two almost untouched, even at very high doses ^[1]. That clean, single-target action is why researchers call it selective. Real human data is thin: one published clinical trial, for recovery of gut function after surgery, did not beat placebo ^[3]. There is no long-term human safety record, and what people report — including the downsides — is gathered on the effects page. This site reads the studies plainly and cites every figure.

What the ipamorelin literature actually shows

In its founding study, ipamorelin released growth hormone in rat pituitary cells, anaesthetised rats, and conscious pigs with potency on par with the older peptide GHRP-6 (pig half-maximal dose 2.3 nmol/kg versus 3.9 nmol/kg) — yet it did not raise cortisol above the level seen with the body's own releasing hormone, even at doses more than 200-fold above its growth-hormone threshold ^[1]. That single result is the whole identity of the molecule: potent on the growth-hormone axis, quiet everywhere else.

The selectivity comes from where it binds. Ipamorelin is a ghrelin-receptor agonist — it activates GHS-R1a (the growth hormone secretagogue receptor type 1a), a separate pathway from the one growth-hormone-releasing hormone uses. Because the two routes are independent, they add together, which is the entire rationale for pairing ipamorelin with a GHRH analog such as CJC-1295 ^[11].

The rodent record is consistent and quantitative. Over 15 days, subcutaneous ipamorelin raised the longitudinal bone-growth rate of adult rats from 42 to 52 micrometres per day at the top dose — and did so without measurably raising circulating IGF-1, the usual downstream growth signal ^[4]. The clean pulse, not a sustained flood, appears to be the mechanism.

The honest state of the human evidence

Human pharmacology is well characterised but narrow. A volunteer study mapped dose-proportional kinetics and a terminal half-life of roughly two hours, with the growth-hormone response arriving as one discrete pulse peaking about 40 minutes after dosing ^[2]. That is essentially the entire clean human dataset.

Efficacy is where the story turns sober. The only published Phase 2 trial gave ipamorelin to 114 adults recovering from bowel surgery and missed its primary endpoint — median time to the first tolerated meal was 25.3 hours on ipamorelin versus 32.6 hours on placebo, a difference that was not statistically significant ^[3]. No specific safety signal emerged in that short window, but neither did proof that it worked. There are no completed Phase 3 trials and no approved indication anywhere.

This is the line the site holds: the mechanism is elegant and reproducible in animals; the human efficacy case is, so far, unproven. Both halves are true, and a forward-looking reader deserves both. The full Ipamorelin research page lays out every study; the Ipamorelin effects page covers what people report and where the cautions lie.

What this site is — and is not

Ipamorelin is not approved as a drug by any regulatory authority, and in 2024 the FDA removed ipamorelin acetate from Category 2 of its interim 503A bulk-substances list and reviewed it at an October advisory-committee meeting, tightening compounding-pharmacy access. It is also banned in sport at all times under the World Anti-Doping Agency's category S2.

The word safe in this domain is a question this site answers honestly, not a verdict it sells. The selectivity record is genuinely favourable on cortisol and prolactin ^[1]; the long-term human safety record simply does not exist yet, and a class-level cardiac signal in a related compound is a real reason for caution ^[6]. We summarise published research. We are not a clinic, we sell nothing, and you will find no dosing instructions here — the doses below are described as they were given to animals or trial volunteers, in the third person, and never as advice. Browse the Ipamorelin references to check the primary sources yourself.