Tesamorelin and Ipamorelin: Two Receptor Classes and What the Literature Reports

Introduction

Tesamorelin is a synthetic 44-amino-acid analogue of human growth-hormone-releasing hormone (GHRH) that acts at the GHRH receptor, and ipamorelin is a synthetic five-amino-acid growth-hormone-releasing peptide (GHRP) that acts at the ghrelin receptor GHS-R1a. The two compounds belong to different pharmacological classes, and no published clinical trial has evaluated them in combination. This article classifies each compound and reports what the peer-reviewed literature says about GHRH analogues co-administered with GHRPs.

Key facts

• Tesamorelin comprises the 44-amino-acid sequence of human GHRH with a hexenoyl group on the N-terminal tyrosine; its molecular weight as free base is 5,135.9 daltons according to the FDA label [1].
• Ipamorelin is the pentapeptide Aib-His-D-2-Nal-D-Phe-Lys-NH2, first described by Raun and colleagues at Novo Nordisk in 1998 [2].
• The GHRH receptor was defined by the 1982 isolation of GHRH by Guillemin and colleagues [3]; the GHS-R1a receptor was cloned by Howard and colleagues in 1996 [4] and its natural ligand ghrelin was identified by Kojima and colleagues in 1999 [5].
• The FDA approved tesamorelin on November 10, 2010 (NDA 022505) as Egrifta, "indicated for the reduction of excess abdominal fat in HIV-infected patients with lipodystrophy" [1].
• Ipamorelin holds no marketing approval from the FDA or the European Medicines Agency; its only published late-stage human study is a 2014 phase 2 trial by Beck and colleagues [6].
• Cheng and colleagues reported in 1989 that GHRP-6 and GHRH produced a synergistic effect on growth hormone release in rat pituitary cells [7]; Bowers and colleagues reported synergistic release in normal men in 1990 [8].
• A PubMed search in September 2026 returned no clinical trial and no animal study of tesamorelin co-administered with ipamorelin.

What are tesamorelin and ipamorelin?

Tesamorelin (development code TH9507; brand name Egrifta) is a GHRH analogue and ipamorelin (development code NNC 26-0161) is a GHRP; they are unrelated molecules. Tesamorelin retains the complete human GHRH(1-44) amide sequence and adds a trans-3-hexenoyl group to the first residue, tyrosine [1]. Ferdinandi and colleagues reported in 2007 that this modification made the peptide resistant to dipeptidyl peptidase-IV and prolonged its plasma elimination relative to native GHRH [9].

Ipamorelin emerged from a medicinal-chemistry program at Novo Nordisk. Raun and colleagues reported in 1998 that the pentapeptide released growth hormone in rat pituitary cells, rats and swine with potency similar to GHRP-6, that antagonist profiling showed it acted through a GHRP-like receptor rather than the GHRH receptor, and that, unlike GHRP-6 and GHRP-2, it did not raise ACTH or cortisol in swine to levels significantly different from those after GHRH [2].

Tesamorelin is not a steroid; it is a peptide acting at a class B G protein-coupled receptor. Ipamorelin is not a GHRH analogue; it is a peptide acting at a class A G protein-coupled receptor. Fuller profiles are in the tesamorelin research overview and the ipamorelin research overview.

Why are tesamorelin and ipamorelin discussed together?

Tesamorelin and ipamorelin are discussed together because they represent the two distinct receptor classes that act on pituitary somatotrophs. GHRH, isolated by Guillemin and colleagues in 1982, acts at the GHRH receptor, which signals through Gs and cyclic AMP [3]. The GHRPs, beginning with the hexapeptide GHRP-6 described by Bowers and colleagues in 1984 [10], act at a separate receptor that Howard and colleagues cloned in 1996 and named GHS-R1a [4]. Kojima and colleagues then identified ghrelin as the receptor's natural ligand in 1999 [5].

Because the two receptor systems are independent, endocrinologists have used a GHRH analogue and a GHRP side by side as pharmacological probes of growth hormone regulation since the late 1980s [7, 8], a body of work reviewed by Ghigo, Arvat and colleagues in 1997 [11]. The class distinction is set out in the library's article on growth hormone secretagogues versus GHRH analogues.

Search interest in "tesamorelin ipamorelin blend" or "tesa/ipa blend" reflects products marketed by other vendors under those names. Sparta Labs supplies tesamorelin and ipamorelin separately as research-use-only reference materials; this article describes the published literature and does not evaluate any third-party product. The same framing applies to searches pairing tesamorelin with sermorelin, another GHRH analogue, which is compared structurally in tesamorelin vs sermorelin.

What has published research reported on GHRH analogues administered with GHRPs?

Published research has consistently reported that co-administration of GHRH with a GHRP produced a larger growth hormone response than either compound alone, in cell culture, in animals and in humans. The studies below used GHRP-6, GHRP-2 or hexarelin, not ipamorelin, and native GHRH or its 1-29 fragment, not tesamorelin. Findings from research models do not establish safety or efficacy in humans. Sparta Labs makes no claims about the use of these compounds.

Authors (year)	Compounds	Model	Reported finding
Cheng et al. (1989) [7]	GHRP-6 + GRF (GHRH)	Rat primary pituitary cells	Synergistic growth hormone release; GHRP-6 potentiated the GHRH-induced cAMP rise; two receptors concluded
Bowers et al. (1990) [8]	GHRP-6 + GHRH(1-44)-NH2	18 normal men	Submaximal GHRP-6 plus GHRH released growth hormone synergistically; independent actions concluded
Peñalva et al. (1993) [12]	GHRP-6 + GHRH	Normal men	Combined response considerably greater than either compound alone (P < 0.01)
Cordido et al. (1993) [13]	GHRP-6 + GHRH	19 obese adults	Combined administration produced a growth hormone discharge described as massive and synergic
Arvat et al. (1997) [14]	Hexarelin + GHRH	Six normal men	A low hexarelin concentration potentiated the GHRH-induced growth hormone response
Popovic et al. (2000) [15]	GHRP-6 + GHRH	125 adults with pituitary disease, 125 controls	Combined GHRH/GHRP-6 test separated GH-deficient adults from controls more clearly than the insulin tolerance test
Arvat et al. (2001) [16]	Ghrelin + GHRH; ghrelin + hexarelin	Seven normal men	Ghrelin plus GHRH synergistic; ghrelin plus hexarelin (same receptor) not additive

Cheng and colleagues at Merck reported in 1989 that GHRP-6 and GHRH together in rat pituitary cell culture produced a synergistic effect on growth hormone release, and that GHRP-6 potentiated the GHRH-induced rise in cyclic AMP while having no effect on cyclic AMP alone [7]. Bowers and colleagues reported in 1990 that submaximal amounts of GHRP-6 given with GHRH(1-44)-NH2 released growth hormone synergistically in 18 normal men [8]. Both groups read synergy as evidence of independent mechanisms.

Peñalva and Cordido and their colleagues reported the same pattern in normal and obese adults in 1993 [12, 13], Arvat and colleagues reported that a low hexarelin concentration potentiated the GHRH response in 1997 [14], and Popovic and colleagues used GHRH plus GHRP-6 as a diagnostic test in 250 adults in The Lancet in 2000 [15].

After ghrelin was identified, Arvat and colleagues reported in 2001 that ghrelin with GHRH in seven normal men had a synergistic effect on growth hormone secretion, while ghrelin with hexarelin, two ligands of the same receptor, did not add [16]. That result indicates the synergy depends on engaging two different receptors.

Has tesamorelin with ipamorelin been studied in a clinical trial?

No. As of a PubMed search conducted in September 2026, no clinical trial, and no animal or in vitro study, has been published that evaluated tesamorelin co-administered with ipamorelin. The search for both names returned only 2026 narrative reviews on peptides in sports medicine, none reporting original data on the pair. Every study in the table above used a different GHRP and native GHRH or GHRH(1-29) rather than tesamorelin.

The two compounds also have separate clinical records. Tesamorelin's human data come from Theratechnologies' phase 3 program, summarized by Grunfeld and colleagues in 2011 [17], and from a 2011 study by Stanley and colleagues reporting that endogenous growth hormone pulsatility persisted during tesamorelin administration in healthy men [18]. Ipamorelin's human data come from early-phase work and the 2014 phase 2 trial by Beck and colleagues [6]. Whether findings on GHRP-6 or hexarelin with native GHRH would transfer to this pair has not been tested.

How do tesamorelin and ipamorelin differ structurally?

Tesamorelin is a 44-residue peptide derived directly from the human GHRH sequence, while ipamorelin is a five-residue synthetic sequence with no natural counterpart. The table summarizes the published identifiers; a fuller side-by-side comparison is in tesamorelin vs ipamorelin.

Property	Tesamorelin	Ipamorelin
Class	GHRH analogue	Growth-hormone-releasing peptide (GHRP)
Receptor	GHRH receptor (class B GPCR, Gs/cAMP) [3]	GHS-R1a, the ghrelin receptor (class A GPCR, Gq/PLC) [4, 5]
Length	44 amino acids [1]	5 amino acids [2]
Sequence basis	Human GHRH(1-44) amide with N-terminal trans-3-hexenoyl group [1, 9]	Aib-His-D-2-Nal-D-Phe-Lys-NH2, designed from the GHRP-1 scaffold [2]
Non-natural residues	None; only the acyl cap is non-native [1]	Aib, D-2-naphthylalanine, D-phenylalanine [2]
Molecular weight	5,135.9 Da (free base) [1]	About 712 Da [2]
Stabilization reported	DPP-IV resistance from the hexenoyl cap [9]	D-amino acids; plasma clearance five-fold lower than GHRP-6 in rats [19]
Developer	Theratechnologies Inc., Montreal [9]	Novo Nordisk A/S, Denmark [2]
Regulatory status	FDA-approved 2010 as Egrifta for one labeled indication [1]	No approval in any jurisdiction; phase 2 data only [6]

Ferdinandi and colleagues reported an apparent elimination half-life of 21 to 45 minutes for tesamorelin in dogs [9]; Johansen and colleagues reported ipamorelin's plasma clearance in rats as five-fold lower than GHRP-6's [19]. These are animal pharmacokinetic observations about the molecules, not any use.

How are the two supplied as research materials?

Sparta Labs supplies tesamorelin and ipamorelin as two separate research-use-only reference materials, each as a lyophilized solid with a batch-specific certificate of analysis. Research-grade tesamorelin is not the FDA-approved drug product Egrifta, and research-grade ipamorelin is not a pharmaceutical of any kind. Neither material is a combined product, and this article does not describe a procedure for combining them.

The phrase "tesa/ipa blend" that appears in search results refers to products marketed by other vendors. Sparta Labs does not evaluate those products, and nothing in the literature above concerns them. Compound-specific questions are collected in the tesamorelin FAQ and the ipamorelin FAQ.

Summary

Tesamorelin is a 44-amino-acid GHRH analogue acting at the GHRH receptor, approved by the FDA in 2010 as Egrifta for one labeled indication; ipamorelin is an unapproved five-amino-acid GHRP acting at the ghrelin receptor GHS-R1a. Published research from Cheng (1989) through Arvat (2001) reported synergistic growth hormone release when GHRH was co-administered with a GHRP, attributed to two independent receptors. None of those studies used tesamorelin or ipamorelin, and no study of that pair exists. Sparta Labs supplies each compound separately as research-use-only reference material.

References

1. Theratechnologies Inc. EGRIFTA (tesamorelin for injection) prescribing information. NDA 022505, approved November 10, 2010. U.S. Food and Drug Administration. Source: accessdata.fda.gov
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