Sermorelin is the minimal bioactive GHRH fragment (residues 1–29); tesamorelin is a stabilised full-length GHRH(1–44) analogue with an N-terminal trans-3-hexenoic acid group that confers resistance to dipeptidylpeptidase IV (DPP-IV) cleavage and a significantly longer duration of GH-stimulating action.
Research reference only — all information on this page summarises peer-reviewed scientific literature and does not constitute medical advice. View full compound profiles: Sermorelin · Tesamorelin
Mechanism Comparison
Both compounds bind the GHRH receptor (GHRHR), a Gs-coupled receptor on pituitary somatotrophs, and stimulate GH synthesis and pulsatile secretion via cAMP/PKA signalling. Sermorelin (GHRH 1–29-NH₂) contains the minimal receptor-binding and receptor-activating domain of endogenous GHRH; it is rapidly inactivated by DPP-IV cleavage at the Ala²–Asp³ bond, giving a plasma half-life of approximately 10–12 minutes. Tesamorelin incorporates a trans-3-hexenoic acid N-terminal modification on the same GHRH(1–44) backbone, blocking DPP-IV access to the Tyr¹–Ala² cleavage site and extending plasma half-life to approximately 26–38 minutes. Tesamorelin's larger peptide backbone (44 AA vs 29 AA) additionally engages receptor-stabilising contacts outside the minimal binding domain, potentially contributing to its sustained GH-stimulating effect in vivo.
Side-by-Side Attributes
| Attribute | Sermorelin | Tesamorelin |
|---|---|---|
| Peptide length | 29 amino acids (GHRH 1–29) | 44 amino acids (GHRH 1–44 + modification) |
| N-terminal modification | None — native GHRH sequence | Trans-3-hexenoic acid (DPP-IV stabilisation) |
| CAS number | 86168-78-7 | 218949-48-9 |
| Molecular weight (approx.) | ~3,357 Da | ~5,135 Da |
| Plasma half-life | ~10–12 min (DPP-IV sensitive) | ~26–38 min (DPP-IV resistant) |
| GH secretion pattern | Pulsatile — mimics physiological GH pulse | Sustained pulsatile — extends GH pulse amplitude and duration |
| FDA regulatory status | Withdrawn (Geref, 2008); investigational only | FDA-approved (Egrifta®, 2010) — HIV-associated lipodystrophy |
| IGF-1 elevation | Modest; mirrors GH pulse magnitude | Greater sustained IGF-1 elevation in Phase 3 trials (IGLOO study) |
| Primary research utility | GHRHR pharmacology; pulsatile GH secretion models | Visceral adipose biology; lipodystrophy models; GH axis research |
Key Research Points
- 1Sermorelin contains only the 29 residues required for full GHRHR binding and activation — it is the smallest GHRH fragment with complete agonist activity. Its rapid DPP-IV degradation gives a plasma half-life of ~10–12 minutes, making it useful in protocols designed to study acute, pulsatile GH secretion kinetics.
- 2Tesamorelin's trans-3-hexenoic acid modification at the N-terminus blocks the primary DPP-IV cleavage site (between Tyr¹ and Ala²) and more than doubles plasma half-life versus native GHRH analogues. This modification was central to obtaining adequate pharmacokinetic properties for FDA approval.
- 3The IGLOO trial (Stanley et al., JCEM, 2014) and Phase 3 lipodystrophy studies demonstrated tesamorelin's ability to significantly reduce visceral adipose tissue (VAT) and sustain elevated IGF-1 levels over 26 weeks — efficacy data that sermorelin lacks in equivalent controlled trial formats.
- 4Both compounds act upstream of the GH/IGF-1 axis (at the level of the pituitary), preserving the physiological feedback loop (rising GH and IGF-1 suppress further GHRHR signalling). This distinguishes them from direct GH administration and from ghrelin-mimetic secretagogues (ipamorelin, GHRP-2) that act at a separate pituitary receptor (GHS-R1a).
- 5Research combining a GHRH analogue (sermorelin or tesamorelin) with a GHS-R1a agonist (ipamorelin) has been studied for synergistic GH release — the two receptor systems act independently and their combined activation produces supra-additive GH secretion in rodent models.
Frequently Asked Questions
What is the difference between sermorelin and tesamorelin?
Sermorelin is a 29-amino-acid synthetic analogue representing the minimal bioactive fragment of endogenous growth hormone-releasing hormone (GHRH 1–29-NH₂). Tesamorelin is a 44-amino-acid stabilised GHRH analogue with an N-terminal trans-3-hexenoic acid modification that protects against dipeptidylpeptidase IV (DPP-IV) cleavage, extending its plasma half-life from approximately 10–12 minutes (sermorelin) to 26–38 minutes. Tesamorelin is FDA-approved for HIV-associated lipodystrophy (Egrifta®, 2010); sermorelin was withdrawn from the US market in 2008. Both stimulate pituitary GHRH receptors to drive pulsatile GH secretion.
Why was sermorelin withdrawn from the market?
Sermorelin acetate (Geref®, Serono) was voluntarily withdrawn from the US market by the manufacturer in 2008, not due to safety concerns but due to commercial reasons — specifically, declining market demand and the availability of recombinant human GH (rhGH) as a more direct intervention. The compound remains pharmacologically active and is available as a compounded peptide for research purposes. FDA approved sermorelin for diagnostic evaluation of GH deficiency in children and, off-label, in adults.
Does tesamorelin increase IGF-1 levels?
Yes. Phase 3 clinical trial data (Falutz et al., NEJM, 2007 and 2010) demonstrated that tesamorelin 2 mg/day subcutaneously produced statistically significant increases in IGF-1 levels compared to placebo in HIV-infected adults with lipodystrophy. IGF-1 elevations were sustained over 26 weeks and reversed upon drug discontinuation, consistent with tesamorelin's mechanism of pulsatile GH stimulation rather than direct IGF-1 administration. The IGLOO extension study (Stanley et al., JCEM, 2014) confirmed sustained IGF-1 elevation at 52 weeks.
Deep Dive
For extended mechanism analysis, trial data, and regulatory context, see the full research article:
Growth Hormone Secretagogues: Sermorelin, CJC-1295, and Ipamorelin Explained →Full compound profile
Sermorelin
Full compound profile
Tesamorelin