Tesamorelin vs Ipamorelin — GRF Analogue vs Pentapeptide

What is the difference between tesamorelin and ipamorelin?

Tesamorelin is a synthetic 44-residue analogue of growth hormone releasing factor (GRF 1-44). Ipamorelin is a synthetic pentapeptide studied as a growth hormone secretagogue. The size difference alone — roughly 5135.9 g/mol versus 711.9 g/mol — reflects how different the two molecules are.

They also belong to different receptor classes. Tesamorelin is characterised as a ligand of the GHRH receptor, the same receptor that native GRF binds. Ipamorelin is characterised at the growth hormone secretagogue receptor (GHS-R1a), whose endogenous ligand is ghrelin. The two names are often compared because both sit on the growth-hormone axis, not because the molecules resemble each other.

How big is each molecule?

Tesamorelin carries all 44 amino acids of human GRF, capped with an amide at the C-terminus and a six-carbon hexenoyl group at the N-terminus. Ipamorelin is five residues long, and three of those five are not among the twenty standard amino acids. Laid side by side, one residue per bead, the gap is hard to miss.

What is tesamorelin?

Tesamorelin (developer code TH9507, PubChem CID 16137828) has the molecular formula C221H366N72O67S. Its sequence is identical to human GRF(1-44)-NH2; the only structural change is the trans-3-hexenoyl group on the tyrosine at position 1. The published literature describes that modification as protecting the N-terminus from enzymatic cleavage, the main route by which native GRF is broken down.

Tesamorelin is CAS 218949-48-5; ipamorelin is CAS 170851-70-4. Both are supplied as lyophilised powders and are commonly handled as acetate salts; the exact form is recorded on each batch's certificate of analysis. A separate salt-form registry number, 804475-66-9, is also in circulation for tesamorelin, so always state which basis a mass figure is quoted on.

One detail matters on the bench: the methionine at position 27 is the molecule's most oxidation-prone site. That is why tesamorelin reference material is kept sealed, cold and away from light, and why an oxidised variant (+16 Da) is one of the impurities an identity check looks for.

What is ipamorelin?

Ipamorelin (PubChem CID 9831659, formula C38H49N9O5) is the pentapeptide Aib-His-D-2-Nal-D-Phe-Lys-NH2. Aib is α-aminoisobutyric acid, D-2-Nal is 3-(2-naphthyl)-D-alanine, and the D-configured residues are a deliberate design choice: they are not recognised by most peptidases, which makes a short peptide more stable than an all-L sequence of the same length.

It was developed under the code NNC 26-0161 and first characterised by Raun et al. (Eur J Endocrinol, 1998) in receptor-pharmacology studies.

Which receptor does each one bind?

The GHRH receptor is a class B G-protein-coupled receptor expressed on somatotroph cells of the anterior pituitary. In receptor assays its signal is read through Gs and cyclic AMP. Tesamorelin, as a full-length GRF analogue, is characterised at this receptor.

GHS-R1a is a class A G-protein-coupled receptor that signals mainly through Gq and intracellular calcium. Its endogenous ligand is the 28-residue acylated peptide ghrelin, and small synthetic secretagogues such as ipamorelin, GHRP-2 and GHRP-6 are characterised against it. Because the two receptors are unrelated, results for one compound say nothing about the other.

What has the published research looked at?

Tesamorelin appears in the published literature as a GRF analogue characterised at the GHRH receptor. Ipamorelin appears in preclinical receptor-pharmacology literature as a GHS-R1a ligand, first described by Raun et al. (1998). The two research contexts are distinct, and Index Peptides takes no position on any application.

This page describes the materials and their documentation only. Neither compound is supplied here as anything other than a laboratory reference material.

How are they handled in the laboratory?

The following are general bench-chemistry notes for research reagents. Both compounds arrive as lyophilised (freeze-dried) powder. Sealed vials are stored frozen, commonly at -20 °C, protected from light and moisture, and allowed to reach room temperature before opening so condensation does not form on the cake.

Once reconstituted in an appropriate laboratory solvent, solutions are held at 2 to 8 °C, aliquoted to avoid repeated freeze-thaw cycles and used within a defined working window. Tesamorelin's larger size and its methionine residue make it the more sensitive of the two; ipamorelin's short, D-residue-rich sequence is comparatively robust. General storage procedures are in the storage guide linked below.

How do you confirm a vial holds the right compound?

The certificate of analysis for the exact lot is the document that substantiates identity and purity. Look for two separate results: chromatographic purity by reverse-phase HPLC, reported as a percentage main peak, and identity by mass spectrometry against the expected mass.

Because the two molecules differ by more than 4,400 Da, a mass spectrum tells them apart immediately. Ipamorelin should show a singly protonated ion near m/z 712.4. Tesamorelin, at about 5136 Da, appears in electrospray MS as a series of multiply charged ions that deconvolute back to that mass. HPLC purity alone cannot confirm which peptide is in the vial — a 99% pure sample of the wrong compound is still the wrong compound.

Supply status

Index Peptides supplies both strictly as research chemicals for in-vitro laboratory research. Products are sold exclusively to qualified researchers and licensed laboratories. Neither is for human or veterinary use.

Frequently asked questions

References

• PubChem — Tesamorelin (CAS 218949-48-5)
• PubChem — Ipamorelin (CAS 170851-70-4)
• Raun K et al. Ipamorelin, the first selective growth hormone secretagogue. Eur J Endocrinol. 1998;139(5):552-61. PMID 9849822