What sermorelin is
Sermorelin (GHRH(1-29)-NH2, also written as GRF(1-29)-NH2) is a synthetic peptide made up of the first 29 amino acids of endogenous growth hormone-releasing hormone (GHRH). Natural GHRH contains 44 amino acids; the N-terminal 29-residue fragment retains full receptor-binding activity and is the minimum biologically active sequence. Molecular weight is approximately 3,358 Da.
The compound was developed as Geref Pediatric by Serono Laboratories. It received FDA approval in 1997 for the treatment of idiopathic growth hormone deficiency in children and for diagnostic testing of pituitary GH reserve. Serono discontinued Geref in 2008 for commercial reasons unrelated to safety or efficacy concerns. Sermorelin has since been used in compounded form for research applications.
Mechanism of action at the pituitary
Sermorelin binds to the GHRH receptor (GHRH-R), a Gs protein-coupled receptor expressed on anterior pituitary somatotroph cells. Binding activates adenylate cyclase, raises intracellular cyclic AMP (cAMP), and activates protein kinase A (PKA). The downstream result is calcium influx and exocytosis of stored GH. GHRH-R expression is largely limited to pituitary somatotrophs, so sermorelin does not trigger hormone release from other pituitary cell types.
Published pharmacological data confirm no measurable changes in prolactin, luteinizing hormone, follicle-stimulating hormone, insulin, cortisol, or blood glucose after sermorelin administration at doses producing robust GH peaks. This selectivity distinguishes sermorelin from ghrelin mimetics such as hexarelin or GHRP-6, which act through GHS-R1a and do affect cortisol and prolactin in some subjects.
Because sermorelin stimulates endogenous GH release rather than introducing exogenous hormone, the resulting GH pulse has a pulsatile character consistent with normal somatotroph secretion. Whether this timing profile confers functional advantages over continuous exogenous rhGH depends on context and remains an open research question.
Sermorelin pharmacokinetics and half-life
The plasma half-life of sermorelin is approximately 11 to 12 minutes after intravenous or subcutaneous administration. The primary pharmacokinetic reference is Wilton and colleagues, published in Acta Paediatrica in 1993 (Wilton P et al., 1993, PubMed 8329825). The study enrolled 30 healthy men aged 19 to 43 years and measured GH responses after intravenous and intranasal GHRH(1-29)-NH2. The lowest IV dose tested (0.25 mcg/kg) produced statistically significant GH release. Maximum GH peaks of approximately 90 mU/L were reached with 1 to 2 mcg/kg. Despite the peptide's rapid elimination, serum GH stayed elevated for approximately 3 hours.
Degradation is driven by dipeptidylpeptidase IV (DPP-IV), which cleaves the Tyr-Ala bond at positions 1 and 2, generating the inactive fragment GRF(3-29). In vitro plasma stability work found intact sermorelin fully degraded within approximately 4 hours. Renal ultrafiltration also contributes to clearance.
A 1994 study by Soule and colleagues in the Journal of Clinical Endocrinology and Metabolism tested how D-Ala2 substitution affected these kinetics in normal men (Soule SG et al., 1994, PubMed 7962295). Replacing alanine at position 2 with D-alanine blocked DPP-IV cleavage, producing a longer disappearance half-time and measurably lower metabolic clearance. This result established N-terminal protection as the primary strategy for extending GHRH analogue half-life and influenced subsequent development of both CJC-1295 and tesamorelin.
Evidence from growth hormone deficiency trials
The most substantial clinical evidence for sermorelin comes from two pediatric GHD trials conducted in the late 1980s and mid-1990s.
An early study treated 18 prepubertal GHD children with twice-daily subcutaneous GHRH(1-29)-NH2 (PubMed 2879138). Height velocity improved in 12 of the 18 children. Eight of those 12 were classified responders, with height velocity gains exceeding 2 cm per year during the first 6 months; individual gains ranged from 2.7 to 11.2 cm/yr. The response was maintained in the responder subgroup across 6 to 18 months of continued treatment.
The pivotal multicenter study was conducted by the Geref International Study Group and published in 1996 (Geref International Study Group, 1996, PubMed 8772599). The trial enrolled 110 previously untreated prepubertal GHD children treated once daily at bedtime with 30 mcg/kg subcutaneous sermorelin. Mean height velocity increased from 4.1 +/- 0.9 cm/yr at baseline to 8.0 +/- 1.5 cm/yr at 6 months and 7.2 +/- 1.3 cm/yr at 12 months. Approximately 74% of the cohort met the threshold for clinically meaningful response within 6 months. This study was central to the FDA approval package for Geref Pediatric in 1997.
Sermorelin was also evaluated as a diagnostic agent. An IV bolus of 1 mcg/kg was studied as an alternative to insulin tolerance testing for pituitary GH reserve assessment. Published comparisons found sermorelin stimulation produced fewer false-positive GH responses in children without GHD than some other provocative agents, though diagnostic performance varied with the GH cutoff applied.
Adult and off-label research
Sermorelin was never approved for adult GH deficiency or age-related GH decline. Off-label and compounded use in adults increased after the pediatric indication was discontinued in 2008.
A published study on growth hormone secretagogue treatment in hypogonadal men (PubMed 28830317) documented that secretagogue administration raises serum IGF-1 in this population. Because GHRH analogues act upstream of the pituitary, serum IGF-1 is the most practical surrogate marker for GH axis activity in adult research settings.
The adult sermorelin evidence base is thin compared to the pediatric record. Most adult GH axis research used recombinant human GH rather than GHRH analogues. Researchers should also note that pituitary responsiveness to GHRH declines with age and varies with baseline hypothalamic GHRH tone, so GH responses in older subjects are generally lower than those seen in pediatric studies.
How sermorelin compares to CJC-1295 and tesamorelin
All three are synthetic GHRH analogues derived from the first 29 amino acids of endogenous GHRH, but their pharmacokinetic profiles differ substantially.
Sermorelin carries the unmodified GHRH(1-29) sequence with an amidated C-terminus and has a plasma half-life of 11 to 12 minutes. See the CJC-1295 and ipamorelin research overview for comparative pharmacology, or the CJC-1295/Ipamorelin compound page for product information.
CJC-1295 with DAC (drug affinity complex) extends half-life to approximately 6 to 8 days by binding covalently to circulating albumin via a maleimide linker at position 29. CJC-1295 without DAC (modified GRF 1-29) lacks that chemistry and has a half-life of roughly 30 minutes.
Tesamorelin achieves DPP-IV resistance through a trans-3-hexenoic acid modification at the N-terminus, giving it a subcutaneous half-life of approximately 26 minutes in adults. It received FDA approval for HIV-associated lipodystrophy as Egrifta, making it the only GHRH analogue with a current regulatory indication.
For research protocol decisions, the relevant question is whether the design requires short GH pulses (sermorelin, 11 to 12 minutes), intermediate release (tesamorelin, modified GRF 1-29), or near-continuous GH elevation (CJC-1295 with DAC). No head-to-head comparative trials between these analogues have been published.
Handling and reconstitution for research use
Sermorelin is supplied as a lyophilized powder requiring reconstitution before use. The standard approach is to add bacteriostatic water slowly along the inside wall of the vial, allow passive dissolution without vigorous mixing, and store the reconstituted solution at 2 to 8 degrees C. The full peptide reconstitution guide covers the protocol step by step. Use the dosing calculator to convert vial mass and added volume into working concentration.
Reconstituted sermorelin is typically reported stable for 20 to 30 days under refrigeration. Given the 11 to 12 minute plasma half-life, research sampling windows aimed at capturing peak GH response should fall within the first 30 to 60 minutes post-administration. The 3-hour GH elevation window documented by Wilton et al. sets a practical ceiling for repeat-sampling designs.
Lyophilized sermorelin does not require cold-chain shipping but should be kept away from light and heat extremes in transit. In tropical research environments such as Indonesia, where ambient temperatures regularly exceed 30 degrees C, refrigerated or frozen storage of lyophilized stock prior to reconstitution is the approach consistent with published peptide stability data.