Sermorelin: A Review of GHRH-Analogue Research

Sermorelin occupies a specific place in the history of growth-hormone research. It was among the first hypothalamic releasing-hormone analogues to reach clinical use, it served for a decade as both a diagnostic agent and a pediatric therapy, and it generated a body of controlled human data in older adults that is still cited in the physiology of aging. It is also a compound whose commercial history is easily misread: the withdrawal of the approved product is sometimes reported as a safety action, which the regulatory record does not support. This note reviews what sermorelin is, how it acts on the growth-hormone axis, what the clinical and preclinical literature recorded, and where the evidence stops. It describes research findings only and does not address any use of research-grade material.

From a pancreatic tumor to a 29-residue peptide

Growth hormone-releasing hormone had been inferred for decades before it was isolated. The pituitary was known to release growth hormone under hypothalamic control, and the inhibitory factor, somatostatin, had been sequenced in 1973, but the stimulatory factor proved elusive because hypothalamic tissue contains it in vanishingly small quantities. The breakthrough came from an unexpected source. In 1982, two groups independently isolated GHRH not from the hypothalamus but from pancreatic tumors in patients with acromegaly, where the tumor was producing the hormone ectopically in large amounts. Guillemin’s group at the Salk Institute characterized a 44-residue peptide from one tumor,¹ and Rivier, Vale and colleagues characterized a 40-residue form from another; Frohman and Jansson’s review recounts both isolations and the structure–activity work that followed.² The 44-residue form, with an amidated C-terminus, was subsequently shown to be the principal hypothalamic species.

Structure–activity work followed quickly. Progressive truncation from the C-terminus showed that the first 29 residues carried essentially all of the receptor-binding and GH-releasing activity; shorter fragments lost potency sharply. GHRH(1-29)-NH₂, the amidated 29-residue fragment, became the standard analogue for clinical development because it was shorter and cheaper to synthesize than the full hormone while retaining full efficacy.³ That fragment is sermorelin. Its sequence is identical to residues 1 through 29 of endogenous human GHRH, which distinguishes it from later analogues such as tesamorelin and CJC-1295 that carry deliberate modifications for stability or extended half-life.

Mechanism of action

Sermorelin binds the GHRH receptor, a G-protein-coupled receptor expressed on somatotroph cells of the anterior pituitary. Receptor activation raises intracellular cyclic AMP, which stimulates both the immediate release of stored growth hormone and, through the transcription factor Pit-1, the transcription of the GH gene and the proliferation of somatotrophs.³ The released GH acts on the liver and peripheral tissues to stimulate production of insulin-like growth factor 1 (IGF-1), which mediates many of GH’s anabolic effects and, together with GH itself, feeds back on the hypothalamus and pituitary to restrain further secretion.

Two features of this mechanism define sermorelin’s pharmacology and distinguish it from exogenous growth hormone. First, it acts upstream: it stimulates the pituitary to release its own GH rather than supplying GH from outside. The response is therefore limited by the pituitary’s secretory capacity, and in a subject whose pituitary cannot make GH, sermorelin does nothing. Second, it preserves pulsatility. GH is normally secreted in discrete pulses, mostly during slow-wave sleep, and the pulse pattern is itself physiologically meaningful. GHRH stimulation produces a pulse; the pulse is then terminated by somatostatin and by GH and IGF-1 feedback. Exogenous GH, by contrast, produces a sustained elevation. Giustina and Veldhuis’s review of GH neuroregulation remains the most thorough account of how GHRH, somatostatin and, later, ghrelin interact to shape these pulses.⁴ Our note on GH, GHRH and GHRP sets out these relationships in more detail.

Sermorelin does not add growth hormone to the system. It asks the pituitary to release what it can, and the feedback loops decide how much that is.

Clinical history: Geref

Sermorelin acetate was developed by Serono and approved by the FDA in the 1990s under the brand name Geref in two forms. A low-dose diagnostic injection was approved for evaluating the pituitary’s ability to secrete GH in suspected growth hormone deficiency: a subject’s GH response to a single administration distinguished pituitary failure from hypothalamic failure, since a pituitary that responded to GHRH was capable of making GH and the deficiency lay upstream. A therapeutic formulation was approved in 1997 for the treatment of idiopathic growth hormone deficiency in children with growth failure. Prakash and Goa’s review in BioDrugs summarized the pediatric trials: in children with GH deficiency whose pituitaries responded to a GHRH challenge, daily sermorelin over 6 to 12 months increased height velocity relative to pretreatment baselines, with the response generally smaller than that seen with recombinant GH but with the advantage of preserving endogenous regulation.⁵ Adverse effects in those trials were predominantly injection-site reactions, flushing and headache.

Both Geref products were later discontinued. The therapeutic formulation was withdrawn from the US market in 2008, and the diagnostic form followed. In March 2013, the FDA published a determination in the Federal Register that Geref, in both therapeutic vial strengths and the diagnostic ampule, “was not withdrawn from sale for reasons of safety or effectiveness.”⁶ This determination is the formal regulatory step that allows generic applications referencing a discontinued product to proceed, and it establishes that the discontinuation was a commercial decision. Recombinant GH had become the dominant therapy for pediatric GH deficiency, and a GHRH analogue that required a responsive pituitary and delivered a smaller growth response occupied a shrinking niche.

Research in older adults

The other major body of human data on sermorelin comes from studies of aging. GH secretion declines with age, a phenomenon sometimes termed the somatopause, and the decline is largely due to reduced GHRH drive and increased somatostatin tone rather than loss of pituitary capacity. That made GHRH(1-29) a natural probe: if the pituitary retained capacity, restoring the stimulus should restore secretion.

Corpas, Harman and Blackman at the National Institute on Aging tested this in the early 1990s. In a study of healthy men aged 60 to 78, twice-daily GHRH(1-29) for 14 days raised 24-hour GH secretion and IGF-1 levels to the range observed in young men, with the increase driven mainly by larger nocturnal pulses.⁷ The pituitary, in other words, had not lost the ability to respond. Vittone and colleagues followed with a placebo-controlled study of single nightly GHRH(1-29) administration over six weeks in healthy older men. They recorded increased GH pulse amplitude and IGF-1, small changes in body composition that did not reach significance across all measures, and improvements in some but not all measures of physical performance.⁸ Khorram and colleagues examined immune parameters in older men and women receiving a norleucine-substituted GHRH(1-29) analogue for 16 weeks and reported changes in several lymphocyte and cytokine measures, the clinical meaning of which remained uncertain.⁹

These studies established the physiological point clearly: the aging pituitary remains responsive to GHRH, and GHRH(1-29) can restore youthful GH and IGF-1 levels in older subjects. What they did not establish was that doing so produced meaningful functional benefit, and the body-composition and performance findings were modest and inconsistent. Walker’s 2006 editorial in Clinical Interventions in Aging argued that sermorelin’s preservation of pulsatility and feedback made it a more physiological approach than exogenous GH for adult-onset GH insufficiency, while acknowledging that outcome data were limited.¹⁰ That remains the state of the evidence: the mechanism is well demonstrated, the clinical value is not.

Evidence type	Population	Design	What was observed
Structure–activity	In vitro, animal pituitary	Fragment comparison	GHRH(1-29)-NH2 retains full GH-releasing activity of GHRH(1-44)
Pediatric clinical	Children with idiopathic GHD	Open-label, 6–12 months	Increased height velocity in GHRH-responsive subjects; smaller effect than rhGH
Diagnostic clinical	Suspected GHD	Single-administration stimulation test	Distinguishes pituitary from hypothalamic GHD
Aging physiology	Healthy men 60–78	14-day, twice daily	GH and IGF-1 restored to young-adult range
Aging, controlled	Healthy older men	Placebo-controlled, 6 weeks	Raised GH pulses and IGF-1; modest, inconsistent body-composition and function changes

Preclinical and mechanistic findings

Because sermorelin is the native GHRH sequence, the preclinical literature on GHRH itself applies to it. GHRH receptor knockout and the naturally occurring little mouse, which carries a loss-of-function mutation in the receptor, show severe dwarfism with reduced somatotroph number, confirming that GHRH signaling is required both for GH release and for normal pituitary development.³ GHRH and its receptor are also expressed outside the pituitary, in the hypothalamus, pancreas, gut, immune cells and some tumors, and a substantial literature has developed on GHRH agonists and antagonists in these tissues. Granata and colleagues’ 2025 review in Nature Reviews Endocrinology summarizes the extrapituitary work, including preclinical studies of GHRH agonists in cardiac and pancreatic islet models and of GHRH antagonists in cancer models.³ Most of this work has used modified agonists with greater stability than sermorelin, and it should not be read as evidence about sermorelin specifically.

Pharmacokinetics and stability

Sermorelin’s principal limitation as a molecule is its short half-life. Native GHRH is cleaved between residues 2 and 3 by dipeptidyl peptidase IV within minutes of entering circulation, and sermorelin, carrying the same N-terminus, is degraded the same way. Its plasma half-life is on the order of 10 to 20 minutes.⁵ This is adequate to trigger a GH pulse, which is the physiological action, but it means each administration produces a single transient stimulus. Later analogues addressed this directly: tesamorelin adds a trans-3-hexenoyl group to the N-terminus to resist DPP-IV, and CJC-1295 replaces several residues and adds a reactive linker that binds serum albumin. These are described in our notes on tesamorelin and CJC-1295 and ipamorelin.

Where the evidence stops

Three limits should be stated. First, the controlled human data on sermorelin in adults are small, short and decades old; no large or long-term outcome trial exists. Second, the pediatric approval rested on growth velocity, a surrogate, and the product was displaced before long-term comparative data against recombinant GH accumulated. Third, all of the human evidence concerns the approved pharmaceutical product administered under clinical supervision, and none of it concerns research-grade material, whose composition is established by analytical testing rather than by regulatory release. Wednesday’s third-party certificates for each lot are in the COA library.

Sermorelin’s research value today is largely as a reference compound: the unmodified native fragment against which stabilized analogues are compared, and a well-characterized tool for probing GHRH-receptor signaling in models. That is a narrower role than its clinical history might suggest, and a more defensible one.

Frequently asked questions

What is sermorelin?

Sermorelin is a synthetic peptide identical to the first 29 amino acids of human growth hormone-releasing hormone, with an amidated C-terminus. It is the shortest GHRH fragment that retains full activity at the GHRH receptor and was formerly marketed as the drug Geref.

How does sermorelin differ from growth hormone?

Growth hormone is the pituitary hormone itself. Sermorelin acts one step upstream, stimulating the pituitary to release its own GH in pulses. Its effect is limited by pituitary capacity and by somatostatin and IGF-1 feedback, whereas exogenous GH bypasses those controls.

Is sermorelin FDA approved?

Not currently. Sermorelin acetate was approved as Geref for diagnostic use and for pediatric growth hormone deficiency in the 1990s. Both products were discontinued, and in 2013 the FDA determined they were not withdrawn for reasons of safety or effectiveness. Research-grade sermorelin is not the approved drug.

What did studies of sermorelin in older adults find?

Short controlled studies in healthy older men found that GHRH(1-29) restored GH pulse amplitude and IGF-1 to young-adult levels, showing the aging pituitary remains responsive. Effects on body composition and physical function were modest and inconsistent, and no long-term outcome data exist.

What is the difference between sermorelin and tesamorelin?

Both are GHRH analogues. Sermorelin is the unmodified 29-residue native fragment with a half-life of minutes. Tesamorelin is the full 44-residue sequence with an N-terminal modification that resists enzymatic breakdown, and it is currently approved as Egrifta for a specific indication.

References & further reading

1. Guillemin R, Brazeau P, Böhlen P, Esch F, Ling N, Wehrenberg WB. Growth hormone-releasing factor from a human pancreatic tumor that caused acromegaly. Science. 1982;218(4572):585-587. doi:10.1126/science.6812220 / PMID 6812220
2. Frohman LA, Jansson JO. Growth hormone-releasing hormone. Endocr Rev. 1986;7(3):223-253. PMID 2874984
3. Granata R, Leone S, Zhang X, et al. Growth hormone-releasing hormone and its analogues in health and disease. Nat Rev Endocrinol. 2025;21(3):180-195. doi:10.1038/s41574-024-01052-1 / PMID 39537825
4. Giustina A, Veldhuis JD. Pathophysiology of the neuroregulation of growth hormone secretion in experimental animals and the human. Endocr Rev. 1998;19(6):717-797. PMID 9861545
5. Prakash A, Goa KL. Sermorelin: a review of its use in the diagnosis and treatment of children with idiopathic growth hormone deficiency. BioDrugs. 1999;12(2):139-157. PMID 18031173
6. US Food and Drug Administration. Determination That GEREF (Sermorelin Acetate) Injection, 0.5 Milligrams Base/Vial and 1.0 Milligrams Base/Vial, and GEREF (Sermorelin Acetate) Injection, 0.05 Milligrams Base/Amp, Were Not Withdrawn From Sale for Reasons of Safety or Effectiveness. Federal Register. 2013;78(42):14091. federalregister.gov
7. Corpas E, Harman SM, Piñeyro MA, Roberson R, Blackman MR. Growth hormone (GH)-releasing hormone-(1-29) twice daily reverses the decreased GH and insulin-like growth factor-I levels in old men. J Clin Endocrinol Metab. 1992;75(2):530-535. academic.oup.com
8. Vittone J, Blackman MR, Busby-Whitehead J, et al. Effects of single nightly injections of growth hormone-releasing hormone (GHRH 1-29) in healthy elderly men. Metabolism. 1997;46(1):89-96. doi:10.1016/S0026-0495(97)90174-8 / PMID 9005976
9. Khorram O, Yeung M, Vu L, Yen SS. Effects of [norleucine27]growth hormone-releasing hormone (GHRH) (1-29)-NH2 administration on the immune system of aging men and women. J Clin Endocrinol Metab. 1997;82(11):3590-3596. academic.oup.com
10. Walker RF. Sermorelin: a better approach to management of adult-onset growth hormone insufficiency? Clin Interv Aging. 2006;1(4):307-308. doi:10.2147/ciia.2006.1.4.307 / PMC2699646