Sermorelin Research Guide: GHRH(1-29), Mechanism, and Geref History

Sermorelin sits at the intersection of peptide identity, receptor biology, early pharmacokinetic research, and an unusually specific U.S. regulatory history. Those evidence lanes are related, but they cannot be collapsed into one claim. A sequence record establishes what the molecule is. A receptor study addresses mechanism. A rat pharmacokinetic experiment addresses one animal model. Geref records describe finished pharmaceutical products that are no longer marketed.

Key takeaways

• Sermorelin is the 29-residue N-terminal GHRH fragment with a C-terminal argininamide; Sermorelin acetate is its acetate material form.
• Reagent identity is fixed and checkable: CAS 86168-78-7, molecular formula C149H246N44O42S, average molecular weight 3357.93 Da, and a 29-residue sequence matching residues 1-29 of the published parent hormone.
• GHRHR is the named receptor, and structural work supports Gs-coupled activation. This mechanism does not establish a clinical outcome.
• An often-repeated short half-life figure comes from an anesthetized-rat experiment and should not be presented as a universal human value. That study measured an elimination half-life of 10.4 min after intravenous dosing.
• The one human measurement in this record used constant intravenous infusion in 10 men and reported a disappearance half-time of 4.3 min, which is a different quantity from a subcutaneous half-life.
• Geref had two U.S. NDAs: a 1990 diagnostic approval and a 1997 pediatric approval. Withdrawal became effective in 2009.
• FDA later determined that the Geref products were not withdrawn for reasons of safety or effectiveness; that determination did not reactivate either approval.
• Historical Geref evidence cannot validate the purity, sterility, activity, safety, or equivalence of a current research-use-only vial.

What Is Sermorelin?

Sermorelin is a synthetic version of the first 29 residues of human growth hormone-releasing hormone, with the C-terminal arginine converted to an amide. The compact notation GHRH(1-29)-NH2 captures both features: residues 1 through 29 of the parent sequence and the terminal amide. The early isolation and characterization of human growth hormone-releasing factor established the 44-residue parent-hormone context.^[1][2]

The FDA Global Substance Registration System records Sermorelin as a defined 29-residue peptide and separately records Sermorelin acetate as a material form. “Acetate” is not an additional peptide residue, and it should not be used to imply a different receptor target. At the same time, material-form naming matters for specifications, molecular-weight calculations, counterion accounting, and analytical documentation.

Where the parent hormone came from

Two 1982 reports characterized a growth hormone-releasing factor recovered from a human pancreatic islet tumour associated with acromegaly. The Science report published the full primary structure of the 44-residue peptide as H-Tyr-Ala-Asp-Ala-Ile-Phe-Thr-Asn-Ser-Tyr-Arg-Lys-Val-Leu-Gly-Gln-Leu-Ser-Ala-Arg-Lys-Leu-Leu-Gln-Asp-Ile-Met-Ser-Arg-Gln-Gln-Gly-Glu-Ser-Asn-Gln-Glu-Arg-Gly-Ala-Arg-Ala-Arg-Leu-NH2 and stated that the synthetic replicate reproduced the biological activity of the natural material in vitro and in vivo for stimulating immunoreactive growth hormone secretion.^[2] The companion Nature report characterized the same tumour-derived factor independently.^[1] Both are structural characterization papers rather than outcome studies, and each reports no quantitative endpoint for the shortened 29-residue construct, which did not yet exist as a named substance.

The practical consequence for identity work is direct. Sermorelin’s 29 residues are the first 29 residues of that published parent structure, and the molecule stops at Arg29 with an amide instead of continuing into Gln30. Any sequence listing that disagrees with the first 29 positions of the 1982 structure is wrong at the identity layer, before any question of purity or activity arises.

What Is the Verified Reagent Identity?

A compound guide is only as useful as the identity block a reader can check independently. Two of the four values below can be verified without leaving the primary record: the sequence is read directly off the 1982 parent structure, and the molecular formula and average mass follow arithmetically from that sequence. The registry number is an index entry maintained by external registries rather than a measurement, and the purity line is a published specification rather than a lot result.

How the mass figure is derived

Summing the residue compositions of the 29 amino acids in the sequence, adding the elements of water for the peptide bond count, and converting the C-terminal acid to an amide gives C149H246N44O42S. Applying standard atomic weights to that formula gives an average mass of 3357.93 Da. The arithmetic is worth stating because it makes the number falsifiable: a reader who disagrees with the composition can recompute it rather than trusting a catalog line.

That figure describes the free peptide. It does not include the acetate counterion, residual water, or any other lot-specific content, so the net peptide content stated on a certificate of analysis will normally be lower than the formula mass would suggest. Peptide content, water content, and counterion content are separate measurements with separate methods, and none of them is implied by the molecular weight.

How Is Sermorelin Signaling Studied?

Sermorelin is studied through the growth hormone-releasing hormone receptor, or GHRHR, often shortened to the GHRH receptor. Molecular cloning identified a pituitary-specific receptor for GHRH, and later structural work resolved how ligand binding organizes activation of this class B G-protein-coupled receptor.^[3][4] The canonical signaling map runs from GHRHR through the stimulatory G protein Gs, adenylyl cyclase, cAMP, and downstream protein-kinase and transcriptional responses.

What the receptor papers actually established

The 1992 cloning study isolated a novel cDNA from rat pituitary mRNA, isolated the human homolog, and expressed it in a human kidney cell line. Membrane fractions from the transfected cells bound human GHRH with high affinity and specificity, and GHRH stimulated intracellular cAMP production in those cells. The encoded protein carries the seven predicted membrane-spanning domains characteristic of G-protein-coupled receptors and is homologous to the secretin and vasoactive intestinal peptide receptors, and the receptor transcript was found predominantly, if not exclusively, in the anterior pituitary.^[3] The 2020 study resolved a cryo-electron-microscopy structure of the human receptor bound to its endogenous ligand and the stimulatory G protein at 2.6-angstrom resolution, showing an extended contact network involving the extracellular domain, every extracellular loop, and all transmembrane helices except TM4, then used mutagenesis and molecular-dynamics simulation to explain how mutations associated with isolated growth hormone deficiency impair receptor function.^[4]

Both papers describe architecture. Neither reports a quantitative endpoint for Sermorelin itself: the cloning study characterizes binding as high-affinity without publishing a dissociation constant for the 29-residue fragment, and the structural study resolves an activation mechanism rather than an effect size. A receptor identity and an activation model are the right foundation for designing an assay. They are not a potency value, and they are not a dose rationale.

Why the receptor map is not a dose rationale

That pathway is mechanistic context, not a clinical shortcut. Receptor engagement in a defined system does not prove an effect in a different cell type, species, formulation, exposure window, or endpoint. It also does not make GHRHR ligands interchangeable. Chain length, terminal chemistry, susceptibility to proteases, and experimental conditions can all change what a study observes.

A further constraint follows from where the receptor sits. Because GHRHR is expressed on pituitary somatotrophs, an agonist at this receptor acts on a cell population that must be present and responsive for anything to be measured at all. Endogenous growth hormone output is episodic rather than steady, and quantifying that pattern requires deconvolution methods designed for pulsatile secretion rather than a single timepoint. Earlier versions of this page attached a specific pulse count per 24-hour period to that observation; no source in the frozen evidence set for this article reports that count, so the figure is not restated here.

What Does the Pharmacokinetic Evidence Show?

Human GHRH is vulnerable to enzymatic cleavage in plasma, including degradation associated with dipeptidyl peptidase IV.^[5] That observation helps explain why GHRH analog research often changes sequence, terminal chemistry, or other structural features. It does not provide a universal half-life for every analog, matrix, species, or route.

The 1989 plasma-degradation study is specific about routes of cleavage. Native GHRH and its C-terminally shortened fragments, including the (1-29) amide, were rapidly cleaved at the 2-3 amide bond, while a fragment starting at position 2 was not degraded at that site. Conversion was unaffected by an aminopeptidase inhibitor and was blocked by a competitive dipeptidylpeptidase-IV inhibitor, which identifies a single-step dipeptidyl cleavage rather than sequential aminopeptidase action. D-amino-acid substitution at position 1 or 2 also prevented hydrolysis. A separate trypsin-like activity cleaved native GHRH at the 11-12 position, with cleavage at 12-13 appearing only for the (1-32) and (1-29) fragments.^[5] That paper maps degradation routes and reports no quantitative result of the effect-size kind; its value is the mechanism, which is why every later half-life-extension strategy targets the N-terminal dipeptide.

The rat half-life figure, stated correctly

A frequently repeated Sermorelin number comes from a 1985 experiment on hGRF(1-29)-NH2 in anesthetized rats. In that study, a homologous radioimmunoassay tracked immunoreactive peptide after a 10 µg intravenous dose, and the disappearance curve was biphasic: the initial distribution phase had a half-life of 1.9 ± 0.2 min and the elimination phase a half-life of 10.4 ± 0.2 min. Subcutaneous dosing produced rapid uptake from the injection site, but comparison of areas under the plasma concentration-time curves showed that only about 4% of the intravenous exposure was recovered in the circulation, which the authors attributed to extensive degradation at the injection site or during transfer to plasma.^[6]

That is the origin of the widely quoted short half-life. It is an elimination half-life measured in anesthetized rats, not a human value, and the broader 10-to-20-minute range that circulates in secondary sources is not stated in the primary abstracts frozen for this article. It is incorrect to remove “rats” from the sentence and present the result as a settled human half-life. The defensible statement is narrower: early rat work found rapid disappearance and poor subcutaneous recovery under those experimental conditions.

What the human infusion data adds

One human dataset in this record measured the unmodified 29-residue amide directly rather than an analog. Ten normal men received constant intravenous infusions, and the study reported both a disappearance half-time of roughly four minutes for GHRH(1-29)-NH2 and a metabolic clearance rate close to twice that of the D-alanine-substituted analog. The exact values, the comparator, the infusion rate, and the statistical results are tabulated in the next section rather than paraphrased here, because a clearance figure without its model and comparator is not usable.

Two cautions apply to all of these numbers. A disappearance half-time measured during and after a constant intravenous infusion is not the same quantity as a subcutaneous elimination half-life, and the two should never be quoted interchangeably. Pharmacokinetic interpretation also depends on what the assay measured: immunoreactive material may not equal intact, receptor-active peptide, and a result can be affected by sampling time, assay specificity, protease activity, adsorption, matrix, and metabolite cross-reactivity. For laboratory planning, the method and model matter as much as the headline number.

Additional Reported Findings

The sources below were cited by an earlier version of this page and are retained here as claim-map rows rather than prose. The point of the format is that a figure, the model it came from, and the source that reported it stay attached to one another instead of drifting apart across paragraphs.

Two housekeeping notes belong with that table. First, six further sources from the earlier version now sit with the pages that own those compounds — the tesamorelin phase 3 trial and its pooled 52-week analysis, the long-acting CJC-1295 pharmacokinetic study, the ipamorelin characterization paper, a pulsatile-secretion methodology review, and a trial of the [Nle27]-substituted GHRH(1-29) analog in older adults. Their readouts stay on those pages so that each compound is described by its own evidence rather than by association.

Second, one source is intentionally not carried forward at all. A 2002 review in Trends in Endocrinology and Metabolism was cited here for a C-terminal truncation series showing that shortened GHRH analogs retain activity down to 29 residues. That review addresses GHRH-driven expansion of the somatotrope lineage and pituitary tumorigenesis and does not report the truncation series it was cited for. The sentence it supported has been removed rather than re-sourced from memory, and the citation is recorded as an intentional drop.

What Was Geref?

Geref was the trade name attached to historical finished Sermorelin drug products in the United States. FDA records show two separate applications. NDA 19-863 was approved on December 28, 1990, for a diagnostic use involving pituitary somatotroph growth-hormone secretory capacity. NDA 20-443 was approved on September 26, 1997, for a pediatric indication involving idiopathic growth-hormone deficiency in children with growth failure.

In 2008, the manufacturer notified FDA that both product lines were being commercially discontinued and requested withdrawal of the applications. The withdrawals became effective June 18, 2009. In a Federal Register notice published March 4, 2013, FDA determined that the products had not been withdrawn from sale for reasons of safety or effectiveness. That determination explains the regulatory reason for withdrawal; it does not mean the products remained marketed, that the NDAs became active again, or that a current research reagent is an approved substitute.

The pediatric evidence on the record

The clinical work behind the second application is published and quantified. A multicenter, open-label study treated 110 previously untreated prepubertal growth-hormone-deficient children for up to one year with 30 µg/kg per day of GHRH(1-29) given subcutaneously at bedtime, and 86 of the 110 were eligible for the efficacy analysis. Mean height velocity for the group rose from 4.1 ± 0.9 cm per year at baseline to 8.0 ± 1.5 cm per year after 6 months and 7.2 ± 1.3 cm per year after 12 months. At the 6-month assessment, 74% of the children were classified as good responders. The ratio of bone-age change to height-age change was not significantly different from unity at 12 months (1.04 ± 0.58; P = 0.63), and no adverse changes in general biochemical or hormonal analyses were reported.^[7]

Those figures describe a regulated finished product administered to a diagnosed pediatric population under a drug application, with defined manufacturing, labeling, and monitoring. They do not transfer to a research reagent, a different formulation, an adult population, a different endpoint, or any present-day use. Reporting them accurately is a matter of historical completeness, not an efficacy claim.

What Regulatory Status Applies Now?

Stated plainly, and per compound rather than per supplier: research-grade Sermorelin acetate holds no FDA, EMA, NMPA, MHRA, PMDA, TGA, Health Canada, or other national regulatory approval in any jurisdiction, for any human or veterinary indication. The two historical United States applications covered specific finished drug products and were withdrawn effective 2009; no approved Sermorelin product has replaced them in the United States since. The fact that a supplier ships research material is a commercial statement, not a regulatory one, and the two should never be presented as if they were the same assertion.

Regulatory status is also time-sensitive. Approvals are granted, withdrawn, and re-determined, and a status line that was correct when an article was written can be stale a year later. The deployment checklist for this page therefore requires a fresh check of the FDA record before publication rather than treating the table above as permanent.

Where Does Sermorelin Sit Among GHRH-Axis Peptides?

Sermorelin belongs to a family of peptides studied at the same receptor, and it is routinely mentioned alongside compounds that are not interchangeable with it. The table below places it structurally without importing anyone else’s data. Cross-compound comparison is a different page type with a different obligation: a comparison has to treat both sides symmetrically, including where evidence is missing, which a single-entity guide cannot do without becoming a comparison in disguise.

The structural column carries the load here. Chain length, terminal chemistry, and conjugation determine how quickly a peptide is cleared, which is exactly what the degradation and infusion studies above measured for the unmodified 29-residue amide. A result obtained with a modified analog describes that analog. Transferring it to Sermorelin would repeat the error the claim-map format exists to prevent.

How Strong Is the Sermorelin Evidence?

The Sermorelin record is strongest where the question is narrow. FDA substance records define identity. Receptor-cloning and structural studies support the GHRHR mechanism. Early pharmacokinetic experiments show rapid degradation in particular models. Historical Geref records document what regulated finished products were approved to do and how those applications were later withdrawn.

Human evidence in this record belongs primarily to historical Geref finished-drug studies and cannot be transferred to a current research reagent. A defensible research design therefore states the material identity, model, exposure window, comparator, endpoint, and analytical checks before interpreting a result.

Those records should not be combined into a broad present-day benefit claim. Historical pediatric and diagnostic studies do not establish efficacy or safety for an unapproved material, a different formulation, a different population, or a different endpoint. Review articles can explain the scientific history, but they do not supersede the primary experiment or the FDA record. The 2006 commentary often cited in this context is a two-page editorial rather than a trial report; it argues a physiologic-stimulus position and reports no quantitative finding of its own.^[8]

What Does This Record Not Establish?

Naming the gaps is part of the evidence summary, not an appendix to it. The following limits apply to every claim on this page.

Species and route. The disposition data are dominated by rat experiments, and the single human dataset used intravenous infusion. Nothing in this record characterizes subcutaneous human exposure for the unmodified 29-residue amide, so no subcutaneous human half-life should be quoted from it.

Assay boundaries. The early work measured immunoreactive peptide by radioimmunoassay. Immunoreactivity is not proof of intact, receptor-active molecule, and cross-reactive metabolites can inflate an apparent concentration. Any modern replication would need to state its analytical method before its numbers can be compared with the historical values.

Model dependence. An agonist acting on pituitary somatotrophs requires a responsive somatotroph population. Studies in models lacking that reserve are not measuring the same thing, and the resulting null results cannot be read as evidence about the molecule.

No comparison with direct replacement. No source in this frozen set compares the 29-residue fragment against recombinant growth hormone on a shared endpoint. Statements that one approach is more physiologic than the other are mechanistic arguments, not measured comparisons.

No evidence about research-grade material. Every human result cited here was generated with a regulated finished pharmaceutical product. No published study in this record evaluates a research-use-only reagent lot, and no literature source establishes the sterility, endotoxin content, stability, or potency of any current vial.

Age of the record. The pharmacokinetic and clinical literature used here spans 1985 to 2005; only the receptor structural work is recent. Where a question depends on current analytical or regulatory facts, the primary record has to be re-checked rather than inherited from an article.

What Can Current Analytical Documents Show?

For a current Sermorelin acetate lot, analytical review begins with the expected material definition. Mass spectrometry can test whether observed ions support the expected mass. Reversed-phase HPLC can report chromatographic purity under a defined method. Those are separate observations: a high HPLC area percentage does not prove sequence identity, and a matching mass does not prove purity or biological activity.

A useful certificate of analysis identifies the lot, method, expected analyte, observed result, date, and acceptance basis. It should not be read as evidence of receptor activation, sterility, clinical safety, or efficacy. The Apex guides to reading a peptide COA and interpreting HPLC purity explain these method boundaries.

The identity table earlier in this guide is the reference point for that review. An observed mass consistent with 3357.93 Da supports the expected free-peptide composition; it does not by itself confirm the residue order, which is why sequence-level confirmation and chromatographic purity are reported as separate lines on a certificate rather than as one number.

Qualified laboratories that have independently defined an appropriate study can consult the current Sermorelin acetate research reagent page and the Lab Verified archive. Product-page stock, pricing, and lot documents should be rechecked at deployment rather than frozen into this editorial guide.

Related Research Guides

This page owns the Sermorelin entity, mechanism, and Geref history. Direct comparisons live in dedicated guides so that each side can be treated symmetrically. See Tesamorelin versus Sermorelin for the 44-residue versus 29-residue comparison, and Sermorelin versus CJC-1295 for a separate GHRH-analog comparison. The growth hormone axis research hub maps adjacent compound families without treating them as substitutes.

Frequently Asked Questions

What is Sermorelin?

Sermorelin is the amidated 29-residue N-terminal fragment of human growth hormone-releasing hormone, commonly written GHRH(1-29)-NH2. Sermorelin acetate is the acetate material form of that defined peptide.

What are the CAS number, formula, and molecular weight of Sermorelin?

The registry number in general use for the free peptide is CAS 86168-78-7. The molecular formula is C149H246N44O42S and the average molecular weight is 3357.93 Da, both derived from the 29-residue amidated sequence. That mass excludes the acetate counterion and any residual water.

What receptor does Sermorelin engage?

Sermorelin is studied as a ligand of the growth hormone-releasing hormone receptor, or GHRHR, a class B G-protein-coupled receptor. Receptor engagement is mechanistic evidence and does not by itself establish a clinical outcome.

Is Sermorelin the same as full-length human GHRH?

No. Human GHRH contains 44 residues, while Sermorelin corresponds to residues 1 through 29 and has a C-terminal amide. The shared N-terminal sequence explains their relationship but does not make the names interchangeable.

What was Geref?

Geref was a historical Sermorelin finished-drug line. FDA approved separate diagnostic and pediatric applications in 1990 and 1997; the products were later discontinued, and withdrawal of both applications became effective in 2009.

What did FDA conclude about why Geref left the market?

FDA determined in 2013 that safety or effectiveness was not the reason the Geref products left sale. That determination did not reactivate the applications or approve present-day research-grade material.

Does Sermorelin have a universal 10-minute half-life?

No universal human value follows from the commonly cited early result. That figure is an elimination half-life of 10.4 minutes measured for hGRF(1-29)-NH2 in anesthetized rats after intravenous dosing, alongside a distribution half-life of 1.9 minutes.

Is there any published human pharmacokinetic value?

One study infused GHRH(1-29)-NH2 intravenously in 10 normal men and reported a disappearance half-time of about 4.3 minutes and a metabolic clearance rate of about 39.7 mL/kg per minute. Those values describe constant intravenous infusion in that study, not a general subcutaneous human half-life.

Does Sermorelin have any current regulatory approval?

No. Research-grade Sermorelin acetate has no FDA, EMA, NMPA or other national regulatory approval anywhere, for any indication. The historical U.S. applications were withdrawn effective 2009 and were not replaced.

What can a Sermorelin COA establish?

A lot-specific COA can document the stated material, methods, chromatographic purity result, and mass-identity result for that lot. It cannot establish receptor activity, sterility, human safety, clinical efficacy, or pharmaceutical equivalence.

References

1. Rivier J, et al. Characterization of a growth hormone-releasing factor from a human pancreatic islet tumour. Nature. 1982;300(5889):276-8. PMID: PMID 6292724.
2. Guillemin R, et al. Growth hormone-releasing factor from a human pancreatic tumor that caused acromegaly. Science. 1982;218(4572):585-7. PMID: PMID 6812220.
3. Mayo KE. Molecular cloning and expression of a pituitary-specific receptor for growth hormone-releasing hormone. Mol Endocrinol. 1992;6(10):1734-44. PMID: PMID 1333056.
4. Zhou F, et al. Structural basis for activation of the growth hormone-releasing hormone receptor. Nat Commun. 2020;11(1):5205. PMID: PMID 33060564.
5. Frohman LA, et al. Dipeptidylpeptidase IV and trypsin-like enzymatic degradation of human growth hormone-releasing hormone in plasma. J Clin Invest. 1989;83(5):1533-40. PMID: PMID 2565342.
6. Rafferty B, et al. Growth hormone-releasing factor analogue (hGRF1-29NH2): immunoreactive-GRF plasma levels after intravenous and subcutaneous administration. J Endocrinol. 1985;107(3):R5-8. PMID: PMID 2866222.
7. Thorner M, et al. Once daily subcutaneous growth hormone-releasing hormone therapy accelerates growth in growth hormone-deficient children during the first year of therapy. Geref International Study Group. J Clin Endocrinol Metab. 1996;81(3):1189-96. PMID: PMID 8772599.
8. Walker RF. Sermorelin: a better approach to management of adult-onset growth hormone insufficiency? Clin Interv Aging. 2006;1(4):307-8. PMID: PMID 18046908.

Written by Nicholas Tremelling

Reviewed by the Apex Laboratory Editorial Team

Reviewed July 25, 2026 for sequence identity, reagent identity arithmetic, receptor mechanism, species-qualified pharmacokinetic figures, claim-map source attribution, Geref dual-NDA history, FDA withdrawal language, per-compound regulatory status, PMID verification, analytical-method boundaries, and research-use framing. See the Apex Laboratory editorial standards.