Tesamorelin: Frequently Asked Research Questions

Introduction

Tesamorelin is a synthetic 44-amino-acid analogue of human growth-hormone-releasing hormone (GHRH), distinguished from the native hormone by a trans-3-hexenoyl group attached to its N-terminal tyrosine. Tesamorelin is a peptide, not a steroid, and it acts as an agonist at the GHRH receptor. The U.S. Food and Drug Administration approved tesamorelin as the prescription drug Egrifta on November 10, 2010; research-grade tesamorelin is a separate research-use-only material.

Key facts

• Tesamorelin is a synthetic analogue of human GHRH(1-44)-NH2, the 44-residue hormone first isolated by Guillemin and colleagues in 1982 [1].
• The molecule differs from native GHRH by a trans-3-hexenoyl moiety, a six-carbon chain with a double bond at position 3, attached to the N-terminal tyrosine [2, 3].
• The molecular formula of the free base is C221H366N72O67S and the free-base molecular weight is 5135.9 daltons, as stated in the FDA-approved label [3].
• The FDA approved tesamorelin (Egrifta, NDA 022505) on November 10, 2010 [8].
• The 2010 label reported a mean elimination half-life of 26 minutes in healthy subjects and 38 minutes in HIV-infected patients [3].
• Ferdinandi and colleagues reported in 2007 that the hexenoyl modification conferred resistance to dipeptidyl aminopeptidase-IV in rat, dog and human plasma [2].
• Research-grade tesamorelin is supplied as a lyophilized research-use-only (RUO) reference material and is not Egrifta.

What is tesamorelin?

Tesamorelin is a synthetic peptide analogue of human growth-hormone-releasing hormone, a 44-amino-acid hypothalamic hormone also called growth-hormone-releasing factor (GRF or GHRF). Guillemin and colleagues first isolated and sequenced the native hormone in 1982 from a human pancreatic tumor [1]. Tesamorelin retains the full 44-residue sequence, amidated at the C-terminus, and adds one modification at the N-terminus [2, 3].

The modification is a trans-3-hexenoyl group, a six-carbon acyl chain with one double bond, bonded to the amino group of tyrosine at position 1 [3]. Theratechnologies developed the molecule under the code name TH9507, and Ferdinandi and colleagues published its non-clinical pharmacology in 2007 [2]. The international nonproprietary name (INN) is tesamorelin [3].

Attribute	Tesamorelin
Class	Synthetic GHRH (GRF) analogue; GHRH-receptor agonist
Length	44 amino acids, C-terminal amide [2, 3]
N-terminal modification	trans-3-hexenoyl on Tyr1 [2, 3]
Molecular formula (free base)	C221H366N72O67S [3]
Molecular weight (free base)	5135.9 daltons [3]
Development code	TH9507 (Theratechnologies) [2]
Approval status	FDA-approved as Egrifta, NDA 022505, November 10, 2010 [8]
Research-grade status	Research use only (RUO); not Egrifta; no approval of its own

Is tesamorelin a peptide or a steroid?

Tesamorelin is a peptide; it is not a steroid. A peptide is a chain of amino acids joined by amide (peptide) bonds, and tesamorelin is a 44-residue chain of that kind. Steroids are lipids built on a four-ring sterane skeleton, contain no amino acids or peptide bonds, and belong to an unrelated chemical class.

The confusion arises because tesamorelin acts on the growth-hormone axis. Tesamorelin is also not growth hormone (somatropin), a 191-residue protein, and not a ghrelin-receptor secretagogue. It is an analogue of the hypothalamic releasing hormone that signals the pituitary, one step upstream of growth hormone itself [1, 6].

How does tesamorelin work?

The reported mechanism is agonism at the GHRH receptor, a class B G-protein-coupled receptor on somatotroph cells of the anterior pituitary [6]. Halmos and colleagues, reviewing GHRH-receptor signaling in 2025, described activation as coupling through Gs to adenylyl cyclase and cyclic AMP, the pathway by which native GHRH stimulates growth-hormone release [6].

The purpose of the hexenoyl modification is enzymatic stability. Frohman and colleagues reported in 1986 that plasma cleaved native GHRH(1-44)-NH2 between residues 2 and 3, producing GHRH(3-44)-NH2 with less than one-thousandth of the parent's activity [4], and in 1989 identified dipeptidyl peptidase IV (DPP-IV) as the responsible enzyme [5].

Ferdinandi and colleagues reported in 2007 that TH9507, modified only by the trans-3-hexenoyl group on Tyr1, resisted DPP-IV deactivation and degraded more slowly than native GHRH in rat, dog and human plasma [2]. In a 2011 study of 13 healthy men, Stanley and colleagues reported that two weeks of tesamorelin administration was associated with higher mean overnight growth hormone and larger GH pulse area, with IGF-1 rising accordingly [7].

Findings from research models do not establish safety or efficacy in humans. Sparta Labs makes no claims about the use of this compound.

Is tesamorelin FDA approved?

Yes. The FDA approved tesamorelin under NDA 022505 on November 10, 2010, with Theratechnologies as sponsor and the trade name Egrifta [8]. The FDA's summary review, dated November 5, 2010, recorded that an advisory panel had voted in favor of approval and that no approved therapy then existed for the proposed indication [9].

The 2010 label states that Egrifta "is indicated for the reduction of excess abdominal fat in HIV-infected adult patients with lipodystrophy" [3]. Later reformulations, Egrifta SV and Egrifta WR, carry the same indication under the same 2010 initial approval date [10].

Research-grade tesamorelin is a different product. It is a research-use-only (RUO) reference material for laboratory work, is not Egrifta, is not manufactured under the Egrifta NDA, and holds no FDA approval of its own. The approval attaches to the specific drug product reviewed, not to the peptide sequence in general.

What is the reported half-life of tesamorelin?

Published and labeled pharmacokinetic data describe tesamorelin as a short-lived peptide with a half-life measured in minutes. The 2010 Egrifta label reported a mean elimination half-life of 26 minutes in healthy subjects and 38 minutes in HIV-infected patients after 14 consecutive days of subcutaneous administration in the clinical pharmacology studies [3]. The Egrifta SV label reported 8 minutes after a single administration of that formulation [10].

González-Sales and colleagues published a population pharmacokinetic analysis of 38 HIV-infected patients and healthy subjects in 2015. They fitted a one-compartment model, estimated plasma clearance at 1,060 liters per hour and volume of distribution at 200 liters, and found that age, body size, race and health status did not predict the pharmacokinetics [11]. In dogs, Ferdinandi and colleagues reported an apparent elimination half-life of 21 to 45 minutes [2].

For context, Frohman and colleagues reported a plasma half-life of 6.8 minutes for native GHRH(1-44)-NH2 after intravenous administration in normal subjects [4]. A pharmacokinetic half-life describes clearance of the parent peptide from plasma, not the duration of any downstream effect.

Does lyophilized tesamorelin need refrigeration?

Storage conditions are a property of a specific formulation and its excipients, not of the peptide name alone. The original 2010 Egrifta label stated that non-reconstituted vials must be stored refrigerated between 2°C and 8°C, protected from light [3]. The later Egrifta SV label states room-temperature storage at 20°C to 25°C, again protected from light [10]. Two labels for the same active ingredient give two different conditions.

The underlying science is that of lyophilized (freeze-dried) peptides. Wang reviewed lyophilization in 2000 and described removal of water as the principal reason solid-state products resist hydrolysis, deamidation and aggregation better than solutions [12]. Carpenter and colleagues described in 1997 how excipients, residual moisture and storage temperature determine the stability of a lyophilized cake [13]. The article on why peptides are lyophilized covers this in more depth.

For research-grade tesamorelin, the applicable storage condition is the one stated per lot by the supplier.

How does tesamorelin differ from sermorelin, CJC-1295 and ipamorelin?

Tesamorelin, sermorelin and CJC-1295 are all GHRH-receptor agonists, whereas ipamorelin acts at a different receptor. The general distinction is covered in growth-hormone secretagogues vs GHRH analogues.

Compound	Class	Backbone	Stabilization chemistry	Receptor
Tesamorelin	GHRH analogue	GHRH(1-44)-NH2	trans-3-hexenoyl on Tyr1 [2, 3]	GHRH receptor
Sermorelin	GHRH analogue	GHRH(1-29)-NH2 [14]	None (native fragment)	GHRH receptor
CJC-1295	GHRH analogue	Substituted GHRH(1-29) [15]	Four substitutions; DAC form adds an albumin-binding linker [15]	GHRH receptor
Ipamorelin	Growth-hormone secretagogue	Aib-His-D-2-Nal-D-Phe-Lys-NH2 (five residues) [16]	Non-natural residues	Ghrelin receptor (GHS-R1a)

Sermorelin is GHRH residues 1 through 29, the shortest fragment with full receptor activity, with no added chemistry [14]. Tesamorelin keeps the whole 44-residue chain and adds the hexenoyl group; see tesamorelin vs sermorelin.

CJC-1295 starts from the same 1-29 fragment but substitutes four residues and, in the DAC (drug affinity complex) form, adds a linker that binds serum albumin. Jetté and colleagues reported in 2005 that this bioconjugate activated the GRF receptor in rats and identified CJC-1295 as a long-lasting analogue [15]. See tesamorelin vs CJC-1295.

Ipamorelin is not a GHRH analogue at all. Raun and colleagues described it in 1998 as a pentapeptide secretagogue acting at the ghrelin receptor that released growth hormone without the ACTH and cortisol release seen with earlier GHRPs [16]. The structural contrast is in tesamorelin vs ipamorelin; the published literature on GHRH-analogue and GHRP co-administration is reviewed in tesamorelin and ipamorelin explained.

Where does research-grade tesamorelin come from?

Research-grade tesamorelin is produced by chemical synthesis. The 44-residue backbone is assembled by solid-phase peptide synthesis, the resin-based method introduced by Merrifield in 1963 [17]. The trans-3-hexenoyl group is then attached to the N-terminal tyrosine, the peptide is cleaved from the resin, and the crude product is purified by reversed-phase HPLC before lyophilization.

Identity and purity are confirmed analytically. Mass spectrometry checks the intact molecule against its expected 5135.9 daltons, which also confirms the hexenoyl group is present, since unmodified GHRH(1-44) would be lighter by that group's mass. Reversed-phase HPLC reports purity, and both results appear on a per-lot certificate of analysis. The tesamorelin catalog listing describes the lyophilized research-grade material; tesamorelin sourcing and quality describes the testing in full.

Research-grade tesamorelin is a research-use-only reference material. It is not Egrifta, is not made under Egrifta's NDA, and is not a substitute for the approved drug.

Summary

Tesamorelin is a synthetic 44-amino-acid analogue of human GHRH with a trans-3-hexenoyl group on its N-terminal tyrosine and a free-base molecular weight of 5135.9 daltons. It is a peptide, not a steroid, and its reported mechanism is agonism at the pituitary GHRH receptor. The FDA approved tesamorelin as Egrifta on November 10, 2010, and the 2010 label reported an elimination half-life of 26 to 38 minutes. Storage conditions depend on the formulation. Research-grade tesamorelin is a separate research-use-only material documented by HPLC and mass spectrometry.

References

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. PMID: 6812220. DOI: 10.1126/science.6812220
2. Ferdinandi ES, Brazeau P, High K, Procter B, Fennell S, Dubreuil P. Non-clinical pharmacology and safety evaluation of TH9507, a human growth hormone-releasing factor analogue. Basic Clin Pharmacol Toxicol. 2007;100(1):49-58. PMID: 17214611. DOI: 10.1111/j.1742-7843.2007.00008.x
3. U.S. Food and Drug Administration. EGRIFTA (tesamorelin for injection) prescribing information, NDA 022505, approved November 2010. FDA label PDF
4. Frohman LA, Downs TR, Williams TC, Heimer EP, Pan YC, Felix AM. Rapid enzymatic degradation of growth hormone-releasing hormone by plasma in vitro and in vivo to a biologically inactive product cleaved at the NH2 terminus. J Clin Invest. 1986;78(4):906-913. PMID: 3093533. DOI: 10.1172/JCI112679
5. Frohman LA, Downs TR, Heimer EP, Felix AM. Dipeptidylpeptidase IV and trypsin-like enzymatic degradation of human growth hormone-releasing hormone in plasma. J Clin Invest. 1989;83(5):1533-1540. PMID: 2565342. DOI: 10.1172/JCI114049
6. Halmos G, Szabo Z, Dobos N, Juhasz E, Schally AV. Growth hormone-releasing hormone receptor (GHRH-R) and its signaling. Rev Endocr Metab Disord. 2025;26(3):343-352. PMID: 39934495. DOI: 10.1007/s11154-025-09952-x
7. Stanley TL, Chen CY, Branch KL, Makimura H, Grinspoon SK. Effects of a growth hormone-releasing hormone analog on endogenous GH pulsatility and insulin sensitivity in healthy men. J Clin Endocrinol Metab. 2011;96(1):150-158. PMID: 20943777. DOI: 10.1210/jc.2010-1587
8. U.S. Food and Drug Administration. NDA 022505 approval letter, EGRIFTA (tesamorelin for injection), November 10, 2010. FDA approval letter PDF
9. U.S. Food and Drug Administration. Summary Review for Regulatory Action, NDA 022505, EGRIFTA (tesamorelin for injection), November 5, 2010. FDA summary review PDF
10. Theratechnologies Inc. EGRIFTA SV (tesamorelin) for injection prescribing information, revised February 2024. DailyMed, U.S. National Library of Medicine. DailyMed label
11. González-Sales M, Barrière O, Tremblay PO, Nekka F, Mamputu JC, Boudreault S, Tanguay M. Population pharmacokinetic analysis of tesamorelin in HIV-infected patients and healthy subjects. Clin Pharmacokinet. 2015;54(3):285-294. PMID: 25358450. DOI: 10.1007/s40262-014-0202-x
12. Wang W. Lyophilization and development of solid protein pharmaceuticals. Int J Pharm. 2000;203(1-2):1-60. PMID: 10967427. DOI: 10.1016/s0378-5173(00)00423-3
13. Carpenter JF, Pikal MJ, Chang BS, Randolph TW. Rational design of stable lyophilized protein formulations: some practical advice. Pharm Res. 1997;14(8):969-975. PMID: 9279875. DOI: 10.1023/a:1012180707283
14. 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. DOI: 10.2165/00063030-199912020-00007
15. Jetté L, Léger R, Thibaudeau K, Benquet C, Robitaille M, Pellerin I, et al. Human growth hormone-releasing factor (hGRF)1-29-albumin bioconjugates activate the GRF receptor on the anterior pituitary in rats: identification of CJC-1295 as a long-lasting GRF analog. Endocrinology. 2005;146(7):3052-3058. PMID: 15817669. DOI: 10.1210/en.2004-1286
16. Raun K, Hansen BS, Johansen NL, Thøgersen H, Madsen K, Ankersen M, Andersen PH. Ipamorelin, the first selective growth hormone secretagogue. Eur J Endocrinol. 1998;139(5):552-561. PMID: 9849822. DOI: 10.1530/eje.0.1390552
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