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Sermorelin vs Ipamorelin: Two Different Receptors

Creator: Priya Raman, Health Writer
Published: 2026-08-26

Sermorelin copies the hypothalamus and clears in about four minutes. Ipamorelin copies ghrelin and lasts roughly two hours. The receptor each one binds explains almost everything else about them.

Priya Raman, Health Writer August 26, 2026 7 min read

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The short version

Sermorelin is GHRH(1-29)NH2 and acts at the GHRH receptor; ipamorelin is a pentapeptide acting at the ghrelin receptor. Same pituitary cells, two separate inputs.
The half-lives are not comparable: GHRH-(1-29)-NH2 disappeared with a half-time of 4.3 minutes in normal men, while ipamorelin's terminal half-life in healthy volunteers was about two hours.
Ipamorelin was the first of its class selective enough to leave ACTH and cortisol unchanged, even at more than 200 times the dose producing half-maximal growth hormone release.
Sermorelin has the deeper human record — a provocative diagnostic test and paediatric growth hormone deficiency treatment; ipamorelin's largest human trial was a phase 2 study in postoperative ileus that did not separate from placebo.
Because the receptors are independent, a GHRH analogue plus a secretagogue released growth hormone synergistically in normal men, which is the pharmacological argument for combining them.
Neither is available as an approved product; both are dispensed as compounded medications, which is different from an FDA-approved product, and a licensed provider decides whether either is appropriate.

Sermorelin vs ipamorelin is a question about two different receptors, not two versions of the same drug. Sermorelin is an analogue of growth hormone-releasing hormone, and it binds the GHRH receptor on the pituitary — the same input the hypothalamus uses. Ipamorelin binds a different receptor entirely: the ghrelin receptor, also called the growth hormone secretagogue receptor. Both end in a pulse of growth hormone released from the same pituitary cells. They arrive there through separate doors, they clear from the body on very different timescales, and those two facts are most of what a prescriber is weighing.

Sermorelin vs ipamorelin: two receptors, two signals

Sermorelin is GHRH(1–29)NH2 — the first 29 amino acids of human growth hormone-releasing hormone, and the shortest synthetic fragment that retains the full biological activity of the natural hormone (Prakash and Goa, BioDrugs 1999). It occupies a receptor the body is already using, so it amplifies an existing signal rather than introducing a new one.

Ipamorelin is a pentapeptide — Aib-His-D-2-Nal-D-Phe-Lys-NH2 — identified at Novo Nordisk within a series of compounds built by removing the central Ala-Trp dipeptide from GHRP-1. Profiling it against GHRH and GHRP antagonists showed that it stimulates growth hormone release through the GHRP-like receptor, not the GHRH receptor (Raun et al., European Journal of Endocrinology 1998).

That paper is also the source of the claim ipamorelin is best known for. Earlier peptides in its class, GHRP-6 and GHRP-2, raised ACTH and cortisol alongside growth hormone. Ipamorelin did not — in conscious swine, ACTH and cortisol stayed at levels no different from those seen after GHRH stimulation, and that held at doses more than 200-fold above the dose producing half-maximal growth hormone release. That selectivity is why it was described as the first selective growth hormone secretagogue.

The half-life gap is large

The two compounds are not on the same clock, and it is not a small difference. Given by constant intravenous infusion to ten healthy men, GHRH-(1–29)-NH2 disappeared with a half-time of 4.3 minutes (Soule et al., Journal of Clinical Endocrinology and Metabolism 1994). Ipamorelin, in a dose-escalation study in healthy male volunteers, showed a terminal half-life of about two hours, with the growth hormone peak arriving around 40 minutes in and then declining (Gobburu et al., Pharmaceutical Research 1999).

	Sermorelin	Ipamorelin
What it is	GHRH(1–29)NH2, a 29-amino-acid analogue of growth hormone-releasing hormone	Aib-His-D-2-Nal-D-Phe-Lys-NH2, a synthetic pentapeptide
Receptor	GHRH receptor on pituitary somatotrophs	Ghrelin receptor (growth hormone secretagogue receptor)
Signal it imitates	Hypothalamic GHRH	Ghrelin
Human half-life	~4 minutes (disappearance half-time, IV infusion)	~2 hours (terminal)
Studied in humans for	Diagnosis of growth hormone deficiency; treatment of idiopathic GHD in children	Healthy-volunteer pharmacokinetics; postoperative ileus (phase 2)
Marketed product	Sold in the US as Geref until 2008; approval withdrawn 2009	None, in any country
Cortisol and ACTH	Not raised	Not raised, even far above the growth hormone-releasing dose

What sermorelin was actually studied in

Sermorelin has the deeper human record of the two, and it is a paediatric and diagnostic record rather than an adult wellness one. A single intravenous dose of 1 microgram per kilogram was used as a provocative test of pituitary growth hormone secretion, producing fewer false-positive results in children without growth hormone deficiency than several other provocative tests. In treatment, once-daily subcutaneous dosing at 30 micrograms per kilogram at bedtime was studied in prepubertal children with idiopathic growth hormone deficiency, with height-velocity increases sustained across 12 months — smaller increases than in children given once-daily somatropin. Transient facial flushing and injection-site pain were the most commonly reported adverse events. Those are trial parameters, not a protocol; the prescriber sets any dose.

The regulatory history is unusually clean and worth stating precisely. Sermorelin was sold in the United States as Geref in two forms: a 0.5 mg and 1.0 mg presentation for treating idiopathic growth hormone deficiency in children with growth failure, and a 0.05 mg presentation for evaluating the pituitary's ability to secrete growth hormone. The manufacturer notified the agency in July and December of 2008 that both were being discontinued, and approval was withdrawn effective 18 June 2009. A notice published on 4 March 2013 recorded the agency's determination that neither presentation had been withdrawn for reasons of safety or effectiveness — the withdrawal was commercial.

What ipamorelin was actually studied in

Ipamorelin's human record is thinner, and honest comparison requires saying so. The pharmacokinetic work above ran five infusion rates with eight healthy men at each level and characterised disposition and the growth hormone response. It was not a treatment trial.

The largest published human trial of ipamorelin was not about growth hormone at all. A multicentre, double-blind, placebo-controlled phase 2 study tested intravenous ipamorelin at 0.03 mg/kg twice daily for up to seven days in 117 adults recovering from bowel resection, on the rationale that ghrelin-receptor stimulation speeds gut motility. Ipamorelin was well tolerated — treatment-emergent adverse events were reported in 87.5% of that group against 94.8% on placebo — but the efficacy result did not separate: median time to tolerating a solid meal was 25.3 hours against 32.6 hours, short of statistical significance (Beck et al., International Journal of Colorectal Disease 2014). Development did not go further, and no ipamorelin product has ever been brought to market. Ipamorelin's studied effects rest almost entirely on that base plus animal work.

Why the two are sometimes paired

Because the receptors are independent, the effects add up rather than overlap. In 18 normal men, submaximal doses of a growth hormone-releasing peptide combined with GHRH stimulated growth hormone release synergistically — more than either produced alone — which the authors read as evidence that the two act through separate systems (Bowers et al., Journal of Clinical Endocrinology and Metabolism 1990).

That is the pharmacological argument for pairing a GHRH analogue with a secretagogue, and it is worth being precise about what it is and is not. The synergy was demonstrated for the class, in acute testing, decades ago. The specific blended preparations dispensed today have not themselves been through combination trials, so the rationale is pharmacological rather than trial-proven. If your question is really about the long-acting GHRH analogue rather than the secretagogue, sermorelin versus CJC-1295 covers that comparison separately.

How a prescriber thinks about the choice

The decision is rarely "which peptide is stronger". It runs closer to this:

Where the problem sits. Both compounds work by asking the pituitary to release growth hormone it can already make; neither replaces the hormone. If the deficit is in the pituitary itself rather than in the hypothalamic signal reaching it, a stimulating peptide is the wrong tool — a question for testing, not for a product page. Sermorelin's studied effects and limits covers what the compound does and does not do.

Clock and burden. A four-minute half-life and a two-hour half-life imply different rhythms. Sermorelin behaves like a brief pulse layered onto the body's own; ipamorelin's exposure is longer.

Other things the receptor does. Ghrelin signalling is not confined to growth hormone; it also drives appetite and gut motility, which is exactly why ipamorelin was trialled in postoperative ileus. That is a reason a prescriber may weigh it differently for someone whose goals involve appetite.

Your history. Growth hormone axis medicines are screened against cancer history, glucose control, thyroid function, pregnancy, current medications, and the state you live in. This is where a request gets declined, and declining is the review working.

What "compounded" means for either compound

Neither compound has an approved product on the US market today, and both reach patients as compounded preparations made by a licensed pharmacy against an individual prescription. Through Promise, sermorelin is dispensed as a compounded medication, which is different from an FDA-approved product: the formulation offered here is not FDA-approved. Compounded medications are not reviewed by the agency for safety, effectiveness or quality.

Regulatory status is one input into a prescribing decision, not the whole of it. A licensed provider may still prescribe a compounded formulation where they judge it appropriate — that decision is between you and your doctor. What that route gives you, and what a vial bought from an anonymous seller does not, is a clinician who read your history, a pharmacy whose output is documented, and someone accountable if something is wrong. Both compounds sit under hormone and organ health, grouped by what they act on rather than by marketing category.

At Promise, a licensed provider reviews every request and prescribes only when it is appropriate for you. Not everyone qualifies.

Common questions

What is the difference between sermorelin and ipamorelin?

They bind different receptors. Sermorelin is a 29-amino-acid analogue of growth hormone-releasing hormone and acts at the GHRH receptor on the pituitary. Ipamorelin is a synthetic pentapeptide acting at the ghrelin receptor, also called the growth hormone secretagogue receptor. Both prompt the same pituitary cells to release growth hormone, but through separate pathways and on very different timescales.

Which lasts longer, sermorelin or ipamorelin?

Ipamorelin, by a wide margin. In healthy male volunteers its terminal half-life was about two hours, with the growth hormone peak roughly 40 minutes after infusion. GHRH-(1-29)-NH2, which is what sermorelin is, disappeared with a half-time of 4.3 minutes when infused intravenously in ten normal men. Sermorelin behaves like a brief pulse; ipamorelin's exposure is far longer.

Why does ipamorelin not raise cortisol?

It was selected for that. Earlier peptides in its class, GHRP-6 and GHRP-2, raised ACTH and cortisol alongside growth hormone. In the 1998 pharmacology work in conscious swine, ipamorelin left ACTH and cortisol no different from GHRH stimulation, even at doses more than 200-fold above the dose giving half-maximal growth hormone release. That is why it was called the first selective growth hormone secretagogue.

Why are sermorelin and ipamorelin sometimes combined?

Because the two receptors are independent, so the signals add. In 18 normal men, submaximal doses of a growth hormone-releasing peptide plus GHRH released growth hormone synergistically, which the authors read as evidence of separate systems. That is a pharmacological rationale demonstrated for the class in acute testing, not a trial result for any specific blended preparation sold today.

Is sermorelin or ipamorelin FDA-approved?

No. Neither has an approved product on the US market today. Sermorelin was sold in the United States as Geref until the manufacturer discontinued it in 2008, and approval was withdrawn in June 2009; a 2013 notice recorded that this was not a safety or effectiveness withdrawal. Ipamorelin has never been marketed anywhere. Both are dispensed as compounded preparations, which is different from an FDA-approved product: what is offered here is not FDA-approved.

Which one would a provider choose?

It depends on the picture, not on which compound is stronger. A provider weighs where the deficit actually sits, since both only prompt release of hormone the pituitary can already make, the dosing rhythm implied by a four-minute versus a two-hour half-life, the ghrelin receptor's other effects on appetite and gut motility, and your history and current medications. Some requests are declined.