Tesamorelin peptide

What the tesamorelin peptide is, in specification terms

A synthetic chain of 44 amino acids carrying one chemical modification at its front end. Written in full it is trans-3-hexenoyl-GRF(1-44)-NH2: the complete sequence of human growth-hormone-releasing hormone, amidated at the C-terminus, with a trans-3-hexenoyl group bonded to the N-terminus. Catalogues and papers also call it TH9507, the development code it carried before it had a name, and GRF(1-44) analogue.

Its molecular formula is C221H366N72O67S and its molecular weight 5135.89 g/mol. It is registered under CAS 218949-48-5. The formula carries a single sulphur atom, so exactly one residue in the chain is sulphur-bearing, which is one of the features a mass-spectrometry identity check has to account for.

Physically it arrives as a white lyophilised cake, soluble in bacteriostatic water, stored at −20°C for the long term and kept out of the light. A cake is not a powder that has been tipped into a vial; it is what remains after the frozen solution has had its water drawn off under vacuum, which is why the material sits as a disc at the bottom rather than as loose granules, and why a cake of lyophilized powder can look cracked or shrunken without anything being wrong with it. It is stocked in 10mg and 20mg tesamorelin vials, released at 99.87% purity by HPLC on the current lot.

By the standards of this catalogue that is a long molecule. Most research peptides sold alongside it are short chains of a few residues, and almost everything difficult about the tesamorelin peptide follows from its length: the synthesis, the purification, the handling and the price. Forty-four residues also sits just under the roughly fifty-residue line at which the word protein takes over, a convention explained in what is a peptide.

The tesamorelin peptide sequence, written out residue by residue

Most catalogues stop at GRF(1-44), which tells a reader the length and nothing else. The chain in full, in three-letter code, is:

trans-3-hexenoyl-Tyr-Ala-Asp-Ala-Ile-Phe-Thr-Asn-Ser-Tyr-Arg-Lys-Val-Leu-Gly-Gln-Leu-Ser-Ala-Arg-Lys-Leu-Leu-Gln-Asp-Ile-Met-Ser-Arg-Gln-Gln-Gly-Glu-Ser-Asn-Gln-Glu-Arg-Gly-Ala-Arg-Ala-Arg-Leu-NH2

In one-letter code the same 44 residues read YADAIFTNSYRKVLGQLSARKLLQDIMSRQQGESNQERGARARL, with the acyl group on the front and the amide on the back.

Two things in that string are worth checking against the formula rather than taking on trust. The first is the methionine at position 27. It is the only sulphur-bearing residue in the chain, and there is no cysteine anywhere in the sequence, which is exactly why the molecular formula ends in a single unsubscripted S rather than S2 or S3. A sequence and a formula that disagree on sulphur count is one of the cheapest errors to catch on a specification sheet, and it is worth catching, because it usually means one of the two was copied from a different molecule.

The second is the start of the chain: Tyr-Ala. An alanine in the second position is the motif dipeptidyl peptidase-4 recognises, and it is the reason the modification sits where it does rather than somewhere else on the molecule. That is covered in the next section.

The trailing -NH2 is not decorative either. An amidated C-terminus means the chain ends in a carboxamide rather than a free carboxylic acid, which changes the mass by about one dalton and the charge state at neutral pH. On a molecule of this size that difference is well inside what LC-MS resolves, so an identity result either confirms the amide or does not.

Why the N-terminus is capped

Native growth-hormone-releasing hormone carries a free amine at the start of its chain, and a free N-terminal amine is the most exposed point on any peptide. It is the end of the molecule that enzymatic attack is described in the literature as reaching first, and the unmodified hormone is characterised there as short-lived for that reason.

The enzyme usually named is dipeptidyl peptidase-4, which removes two residues from the front of a chain when the second of them is an alanine or a proline. Native GHRH begins Tyr-Ala, so it presents that motif directly. Naming the enzyme is worth doing because it explains the geometry of the molecule: the modification is at position one, not somewhere in the middle, because position one is where the cut would be made.

The trans-3-hexenoyl group exists to remove that handle. It is a short unsaturated acyl group joined by an amide bond to the nitrogen that would otherwise be free, so the amine is occupied rather than exposed. The preclinical literature describes this N-terminal modification as extending half-life relative to native GHRH(1-44), and characterises the modified chain as more resistant to that cleavage in plasma-stability preparations.

Two things follow. The sequence underneath is unchanged, so the molecule is still the full 44-residue hormone chain rather than a redesign of it. And the modification is structural, not incidental: a certificate that confirms mass is confirming the capped molecule, because the uncapped chain would weigh something else entirely. An identity check on the tesamorelin peptide is therefore a check on the cap as much as on the sequence.

This is the same logic that puts an acetyl group on much shorter research peptides. The chemistry is modest and the reason is always the same: the free end of a peptide is the part that is easiest to get at.

The tesamorelin peptide against the other molecules on the same shelf

Sermorelin is the compound tesamorelin is most often confused with, and the difference is a matter of how much of the hormone each one keeps.

Sermorelin is GRF(1-29)NH2, the first 29 residues of growth-hormone-releasing hormone, amidated at the C-terminus, roughly 3358 g/mol. The chain simply stops there. The remaining residues of the hormone are not present in the molecule at all, and nothing is attached in their place. Sermorelin is not part of this catalogue.

Tesamorelin keeps all 44 residues and modifies the front of the chain instead of shortening it. One is a fragment of the hormone, the other is the full-length hormone with a cap on it, and the gap between roughly 3358 g/mol and 5135.89 g/mol is the mass of the residues sermorelin does not carry.

CJC-1295 is the third name in this family and it belongs on the sermorelin side of the line, not the tesamorelin side: it is built on the GRF(1-29) scaffold with amino-acid substitutions in the chain, and in its DAC form carries a linker group that is not part of the hormone sequence at all. It is not stocked here either. The structural point is that shortening-plus-substitution and full-length-plus-acylation are two different design answers to the same problem, and a table that lists them side by side makes that visible in a way that three paragraphs do not.

Ipamorelin gets swept into the same paragraph and does not belong there on structure at all. It is a five-residue chain of 711.85 g/mol classed as a ghrelin-receptor agonist rather than as a GHRH analogue. That is a different receptor, a different scaffold, and a molecule roughly one seventh the mass of the tesamorelin peptide. It is stocked, as 5mg and 10mg ipamorelin vials, and the two are dispatched together in the Growth Reference Panel for work that needs both. The three-way comparison in prose is in tesamorelin vs sermorelin vs ipamorelin. Further along the same shelf the gap is wider still: the GHK-Cu copper peptide is three residues at 403.94 g/mol against the 44 residues and 5135.89 g/mol of the tesamorelin peptide.

What the preclinical literature studies

Three study points recur for the tesamorelin peptide, and all of them are model systems rather than statements about people.

The first is receptor pharmacology. Tesamorelin is characterised as an agonist at the growth-hormone-releasing hormone receptor, and that binding is measured in GHRH-receptor-expressing cell lines and in pituitary preparations, the somatotrophs of the anterior pituitary being the tissue the receptor is native to. The mechanism of interest is indirect: the molecule is studied as something that acts on the tissue which makes growth hormone, rather than as growth hormone itself.

The second is visceral adipose tissue, which is the endpoint the compound has been studied against most widely. It appears throughout the literature as a measured tissue endpoint in model systems.

The third is the molecule rather than its pharmacology: comparisons of stability and half-life between the capped peptide and native GHRH(1-44), usually run in plasma preparations and read out by LC-MS fragmentation. That is the work that explains why the N-terminal group is there at all.

There is a fourth use that has nothing to do with pharmacology and is worth naming because it is the one this material is actually sold for. A well-characterised 44-residue peptide with a published mass, a published formula and a lot-matched identity result is a useful reference standard when developing analytical methods for long chains. Most method-development work in this category is done on peptides of five to fifteen residues, which behave differently on a column; the tesamorelin peptide is one of the few compounds on the shelf that sits above forty.

Everything above describes preclinical model systems and laboratory method work. Nothing here describes an effect in a person, and this material is supplied strictly for in-vitro laboratory research.

Why 44 residues is a harder synthesis than a short chain

The tesamorelin peptide, like others of its kind, is built by solid-phase synthesis. The final residue is anchored to a resin bead and the chain grows one residue at a time. Each cycle runs deprotect, couple, wash, repeat, with the bead holding the work in place throughout. Every residue in the sequence has its own cycle, so a chain this long is a long run of them.

No coupling is perfect. Each cycle leaves behind a small proportion of chains that failed to extend, and those failures accumulate with every step, so the fraction of material that made it through untouched falls away as the chain gets longer. This is why purity figures across the short end of this category run so uniformly high, and why a long chain is a genuinely different manufacturing problem rather than the same problem repeated.

The failures are also awkward to remove. A chain missing one residue out of 44 differs from the target by a small fraction of its mass and behaves almost identically on a column, so reversed-phase preparative HPLC has to separate species that are chemically very similar to the thing being purified. Longer chains are more prone to folding and aggregating on the resin as well, which slows the couplings in the middle of a synthesis and makes the problem worse rather than better as the run goes on.

Purification leaves its own mark on the finished vial. Preparative HPLC is normally run with trifluoroacetic acid in the mobile phase, so the peptide comes off the column as a trifluoroacetate salt, and that counter-ion is still in the cake when it is weighed out. It is real mass and it is not peptide, which is the whole reason net peptide content is measured separately from purity.

The last step is the lyophilisation itself. The purified fractions are pooled, frozen, and the water is removed by sublimation under vacuum, which is what leaves the porous disc at the bottom of the vial rather than a dense powder. That porosity is functional: it is why the cake takes up diluent quickly. It is also why the cake's appearance varies between lots without saying anything about the material.

The conclusion people usually draw from all this is backwards. A long peptide is not a reason to accept a softer purity figure; it is the reason the figure has to be measured on the actual lot. On a short chain a high number is close to routine. On a 44-residue chain it is evidence about that specific synthesis, and it says nothing about the next one. What a purity percentage does and does not measure, set out in peptide purity, is worth reading before comparing two catalogue numbers.

Reconstitution, treated as a handling procedure

The cake has to go into solution before it can be assayed, and this is the step at which most laboratory material is damaged. It is worth stating as chemistry rather than as ritual.

The diluent normally used for a lyophilised research peptide is bacteriostatic water: sterile water carrying 0.9% benzyl alcohol as a preservative. The benzyl alcohol is what makes a multi-withdrawal container tolerable at all. Plain sterile water has no preservative and a container of it is a single-use proposition, and the difference between the two diluents is set out in sterile water vs bacteriostatic water. The tesamorelin peptide is specified as soluble in bacteriostatic water, and the reasoning behind that choice, including where it does not apply, is set out in bacteriostatic water for peptides.

Direct the diluent down the inside wall of the vial rather than onto the face of the cake. A stream landing squarely on a porous disc drives it apart mechanically and generates foam, and foam at an air-liquid interface is where peptides denature. Then swirl the vial gently, or roll it between the fingers, until the cake clears. Do not shake it. Shaking is the single most common way a correctly manufactured vial is degraded before it is ever measured.

A properly lyophilised cake usually clears in under a minute. If it does not, the answer is time and gentle agitation rather than force; warming the vial is not the fix, and neither is vortexing.

The arithmetic afterwards is straightforward and it is arithmetic, nothing more. The concentration of the resulting solution is the vial's net peptide content divided by the volume of diluent added. Net peptide content, not the number on the label: the label states a nominal mass and the certificate states the measured peptide fraction, and on lot TESM-052026-4 those are 10mg and 10.57mg respectively. A vial reconstituted in 2mL of diluent therefore yields a stock at 5.29 mg/mL, and a solution prepared from the label figure alone would be quoted about 5% low.

Everything in this section is the preparation of a laboratory stock solution for in-vitro work. It is not a preparation procedure for anything else, and nothing here should be read as one.

Tesamorelin peptide storage and stability, by form

A sealed lyophilised vial and an open reconstituted one are two different materials with two different storage problems, and treating them as one is how a good lot is wasted.

The sealed cake is stable because the water has been taken out of it. Hydrolysis needs water; a dry, sealed, light-protected vial at −20°C has very little of it and very little to react with. That is the whole reason the material is lyophilised rather than shipped as a solution.

Once diluent is added, all of that is undone. The peptide is now in water, at a pH set by the diluent, in a container that has been entered at least once. Refrigeration at 2 to 8°C slows the chemistry down; it does not stop it. Repeated freeze-thaw cycles are worse than either extreme, because each cycle concentrates solutes at the ice front and puts the peptide through a phase boundary it does not need to cross.

We do not publish a shelf-life figure in months for the reconstituted tesamorelin peptide, and the reason is that we have not measured one on this material. Other catalogues print a number; ours would be a guess dressed as data, and the check we would rather a reader ran is the one in how to store peptides, which is written around what actually degrades rather than around a date. The diluent has its own in-use period, which is a separate question and is covered in bacteriostatic water storage.

One practical note about transit, because it is asked constantly: a sealed lyophilised vial is not a cold-chain item. It travels at ambient temperature without harm, which is why vials arrive without dry ice and why that is not a sign of a corner cut. The −20°C figure is a storage condition, not a shipping one.

Five lots, five certificates

Each lot is assayed independently and the certificate is published against the lot number printed on the vial. Five lots have been released and all five certificates are on the site, including for lots long out of stock, which is the part most catalogues quietly skip.

The current lot is TESM-052026-4, a 10mg vial released on 7 Jul 2026 at 99.87% by HPLC, with net peptide content of 10.57mg, identity confirmed by LC-MS and endotoxin passing on both replicates, tested by Freedom Diagnostics. The full history is below.

The lot number is the part that makes the rest of the document mean anything. A certificate for a different batch is somebody else's measurement. Typing the code from the label into the batch lot verifier returns the certificate for that exact vial, and if a number does not resolve, that in itself is the finding.

Net peptide content is the figure most worth understanding, and it is the one most often left off a certificate altogether. Lyophilised peptide is not pure peptide by mass: the cake also contains the trifluoroacetate counter-ion left over from purification and whatever water the material holds. Gross vial mass therefore overstates how much peptide is present, unless somebody has measured the peptide fraction and said so. Every lot above is stated above its 10mg label, between 10.33mg and 11.08mg.

Purity and content are separate measurements and answer separate questions. Purity says what proportion of the peptide present is the intended molecule rather than a deletion sequence or a by-product. Content says how much peptide there is at all. A vial can be excellent on one and unremarkable on the other, which is why the two numbers belong on the same page. Identity is a third question again, and on a molecule of this mass it is the one LC-MS is there to settle.

The spread across those five lots, 99.253% at the bottom and 99.93% at the top, is the ordinary variation of a real manufacturing process reported honestly. It would have been trivial to publish only the two best and call the specification 99.9%. A supplier publishing one figure for the tesamorelin peptide across every batch, year after year, is publishing a specification rather than a measurement, and the two are not the same document.

What each test on the certificate actually answers

A certificate is a set of separate answers to separate questions, and a reader who treats it as one number is reading about a fifth of it. The table below is the honest version, including the two lines where the answer is that we do not publish the test.

The column that matters most is the fourth one. Every analytical method has a blind spot, and a certificate that lists five passes without saying what each pass excludes is a marketing document. Purity by RP-HPLC, for instance, reports the proportion of the material the detector sees at a given wavelength. It is silent about anything that does not absorb there, and silent about how much material is in the vial at all.

We publish four results per lot of the tesamorelin peptide and we do not publish three others. Heavy metals by ICP-MS, sterility by PCR and a controlled-substance screen appear on some competing certificates and not on ours, and rather than let a reader assume, it is better to say so plainly and let them weigh it. How to read a peptide certificate of analysis goes through a real document line by line, and peptide purity testing covers what the methods themselves can and cannot resolve.

Sizes, price and buying the tesamorelin peptide as research material

The tesamorelin peptide is stocked in two sizes and no others: a 10mg vial at $99.99 and a 20mg vial at $189.99. There is no 5mg size. Every certificate on file is for a 10mg lot, which is worth saying outright rather than implying that a 20mg certificate exists somewhere.

It is the most expensive compound per vial in the catalogue, and the reason is the one set out above: 43 coupling cycles, a purification problem that gets harder rather than easier with length, and a yield that falls away accordingly. A short chain at the same price would be a question worth asking; a 44-residue chain at the same price as a pentapeptide would be the more alarming number.

Who it is sold to, and on what terms, is not a formality. This is in-vitro laboratory material. It is not a pharmaceutical, it is not manufactured or released as one, and it is not for human or veterinary use in any form. Handling belongs inside an institutional chemical hygiene plan. If you are weighing one supplier against another, how to vet a research peptide supplier sets out the checks that are worth running before the first order rather than after it.

For work that needs a GHRH analogue and a ghrelin-receptor agonist in the same run, the Growth Reference Panel ships tesamorelin and ipamorelin lot-matched in one dispatch at a 10% discount on the separate vials. Otherwise the tesamorelin product page carries both sizes and the current lot's certificate.