Tesamorelin

Overview

Tesamorelin is a synthetic analogue of growth hormone-releasing hormone, studied for effects on the growth hormone axis and on visceral fat. It is one of the small number of compounds in this catalogue with regulatory approval, and it takes a notably different structural approach from the other GHRH analogues here.

Chemical identity

• Also known as: TH9507
• CAS number: 218949-48-5
• Molecular formula: C₂₂₁H₃₆₆N₇₂O₆₇S
• Molecular weight: 5195.91 g/mol
• Classification: GHRH analogue, GHRH receptor agonist
• Length: 44 residues plus an N-terminal acyl cap
• Appearance: White lyophilised powder

At 5,196 g/mol this is the largest molecule in this catalogue and well beyond the size at which a structural depiction remains readable. The single sulfur atom is one methionine.

Full length, not a fragment

Every GHRH analogue has to solve the same problem: native GHRH is destroyed by dipeptidyl peptidase-4 within minutes. There are two ways to approach it, and this catalogue contains both.

Mod GRF 1-29 takes the reductionist route. Biological activity resides almost entirely in the first 29 residues, so that fragment is kept, the rest discarded, and four amino acid substitutions installed to block the cleavage site and improve stability. The result is a smaller, extensively re-engineered molecule.

Tesamorelin takes the conservative route. It retains the complete 44-residue GHRH sequence unchanged and adds a single modification at the N-terminus: a trans-3-hexenoic acid group attached to the first residue. That cap sits over the site DPP-4 would attack, blocking access without altering any of the amino acids.

Both work. The difference is philosophical — rebuild the molecule, or leave it intact and protect it — and it produces molecules of very different size for the same receptor.

Mechanism of action

Tesamorelin agonises the GHRH receptor on pituitary somatotrophs, signalling through cyclic AMP to trigger growth hormone synthesis and release, with IGF-1 rising downstream. Because it acts on the pituitary rather than supplying growth hormone directly, output remains subject to somatostatin opposition and to IGF-1 negative feedback — the axis retains its own regulation.

The visceral fat findings that led to its approval follow from that: growth hormone influences lipolysis in visceral adipose tissue, and a GHRH analogue increases growth hormone within the constraints of normal regulation rather than overriding them.

Regulatory status

Tesamorelin is an approved prescription medicine, and it is worth being precise about the indication rather than leaving it vague.

It is approved for the reduction of excess abdominal fat in patients with HIV-associated lipodystrophy — a specific metabolic complication in which fat redistributes abnormally, accumulating viscerally. That is a narrow indication. It is not approved as a general growth hormone therapy, nor for body composition in healthy people, and the trial evidence supporting it was generated in that particular population.

The usual consequences follow. Material supplied for laboratory research is not a pharmaceutical product, has not been manufactured or released under the controls governing an approved medicine, and is not a substitute for one.

Research record

• Initial clinical work. Falutz and colleagues reported metabolic effects in patients with HIV-associated fat accumulation, establishing the effect on visceral adipose tissue.
• Confirmatory trials. Subsequent randomised work examined the same population in larger studies, forming the basis for approval.
• Liver fat. Later research examined effects on hepatic fat content, extending the question beyond visceral adipose alone.

The research base is therefore real, randomised and controlled — but concentrated in one clinical population. Extrapolating those findings to other contexts is an assumption rather than an established result.

Reported observations

The findings most reported in trials are injection-site reactions, joint pain and swelling from fluid retention — the last two being effects associated with elevated growth hormone generally rather than with this compound specifically.

Effects on glucose handling are the more substantive consideration. Growth hormone antagonises insulin action, and any compound that raises it sustainedly can be expected to influence glucose tolerance. Trial literature examines this specifically rather than treating it as incidental, which is the right way to read it.

Handling, reconstitution and storage

• Lyophilised storage: sealed, refrigerated, protected from light. Freeze for long-term storage.
• Mechanically fragile. At 44 residues this is a long chain with real secondary structure. Do not shake — foaming denatures large peptides far more readily than short ones.
• Methionine oxidation is the main chemical degradation route, as the single sulfur indicates.
• Reconstitution: add diluent slowly down the vial wall and allow the powder to dissolve undisturbed.
• After reconstitution: refrigerate, protect from light, minimise freeze–thaw cycles.
• Concentration: our peptide reconstitution calculator converts vial quantity, diluent volume and syringe size into concentration per unit.

Purity and analytical verification

Two things make this compound analytically demanding, and the second is not obvious.

Length. Forty-four coupling steps generate a large population of deletion sequences, each chemically similar to the target. A high purity figure on a peptide this long represents substantially more purification work than the same number on a short one, and purity claims should be read with that in mind.

A small modification on a large molecule. The N-terminal cap is what makes this compound work — without it, the peptide is native GHRH with a half-life of minutes rather than a DPP-4-resistant analogue. But that cap contributes only about 96 Da to a molecule of 5,196.

Compare that with semaglutide, where a failed acylation removes several hundred daltons from a smaller peptide. There the absence is glaring. Here it is under two percent of total mass, which needs genuinely good mass accuracy to detect with confidence. A low-resolution figure reported as “approximately 5200” does not establish that the cap is present, and an uncapped batch would be a different compound in every way that matters functionally.

This is the clearest example in the catalogue of a general principle: how easily a modification can be verified depends on its size relative to the molecule carrying it, not on how important it is.

We publish third-party certificates of analysis by batch.

References

• Falutz J, Allas S, Blot K, et al. Metabolic effects of a growth hormone-releasing factor in patients with HIV. New England Journal of Medicine, 2007. PMID 18057338
• Falutz J, Mamputu JC, Potvin D, et al. Effects of tesamorelin, a growth hormone-releasing factor analog, in HIV-infected patients with excess abdominal fat. Journal of Clinical Endocrinology & Metabolism, 2010. PMID 20554713
• Stanley TL, Feldpausch MN, Oh J, et al. Effect of tesamorelin on visceral fat and liver fat in HIV-infected patients with abdominal fat accumulation. JAMA, 2014. PMID 25038357

Summary

Tesamorelin (TH9507) is a GHRH analogue, CAS 218949-48-5, molecular formula C₂₂₁H₃₆₆N₇₂O₆₇S, molecular weight 5,195.91 g/mol — the largest compound in this catalogue. It retains the complete 44-residue GHRH sequence and adds a trans-3-hexenoic acid cap at the N-terminus to block DPP-4 cleavage, the opposite design approach to the truncated and re-engineered CJC-1295 family. It is an approved medicine for a narrow indication, reduction of excess abdominal fat in HIV-associated lipodystrophy, and its clinical evidence comes from that population specifically. Verifying the N-terminal cap requires better mass accuracy than most modifications in this catalogue, because it is small relative to the peptide carrying it.

For laboratory research use only. Not for human consumption. This material is not a drug, food, or cosmetic and may not be sold or used for any purpose other than in vitro or non-human laboratory research. References to clinical studies describe the published scientific literature and are not guidance for use.