Tesamorelin testing: what a lab test shows, published test results and how samples fail

What a tesamorelin test shows

A tesamorelin test should answer three questions. Is the peptide tesamorelin? How pure is it? How many mg does the vial hold? LC-MS answers the first with a mass match, HPLC the second, and a content assay against a reference standard the third. Vials for injection research add endotoxin and sterility.

Test	What it answers for tesamorelin	Reported as
Identity (LC-MS)	Observed mass against the calculated monoisotopic mass, 5132.7166 Da	Expected and observed mass, error in ppm
Purity (HPLC)	Main peak as a share of UV peak area	% area, with the impurity peaks
Content per vial	mg of tesamorelin against a reference standard	mg per vial, basis, uncertainty
Endotoxin (LAL)	Bacterial endotoxin in the sample	EU per mg and EU per vial
Sterility (USP <71>, 14 days)	Microbial growth over 14 days	Growth or no growth

For raw powder, the tesamorelin compound page replaces endotoxin and sterility with counter-ion (TFA, acetate) and water content (Karl Fischer).

Tesamorelin is an analogue of growth hormone-releasing hormone (GHRH). It has 44 amino acids, a trans-3-hexenoyl group on the N-terminus and an amide at the C-terminus. Its formula is C221H366N72O67S and its CAS number is 218949-48-5. An LC-MS run looks for its multiply charged ions, calculated at m/z 1711.9128 (3+), 1284.1864 (4+) and 1027.5506 (5+).

Tesamorelin test results: more than half of published samples fail

Finnrick, a US platform that publishes results from community-submitted samples, gives pass and fail counts by product. In its data to 20 September 2026, tesamorelin had 604 published tests. 274 passed and 326 failed; the other 4 had no pass or fail result. That is a fail share of about 54% of classifiable samples.

Product	Published tests	Failed	Share of classifiable samples that failed
CJC-1295	294	210	72%
Tesamorelin	604	326	54%
BPC-157	791	395	50%
Retatrutide	3,858	824	22%
GHK-Cu	807	104	13%

Finnrick’s default standard, Purity Focus, passes a sample only if the identity is right, purity is at least 99.5%, and the fill is within ±35% of the label claim. Overfill fails as well as underfill. The counts do not say which requirement each sample missed. A tesamorelin “fail” can be a wrong peptide, a vial far from its label, or a purity of 99.0%. The guide to peptide fail rates explains the caveats.

One batch, two labs: 99.985% and 97.779% purity

In August 2026, the Substack writer Krysia published results for one tesamorelin batch tested at two labs. Each lab tested its own vials.

Lab	Purity (HPLC)	Content	Measurements
Freedom Diagnostics	99.985%	10.055 mg	Average of two vials, 0.39 mg apart
Janoshik	97.779%	11.057 mg	Three measurements within 0.02 mg

Purity differed by 2.2 points and content by about 1 mg. On purity alone, under Finnrick’s 99.5% rule, one figure passes and the other fails for the same batch.

The author pointed to a small peak just before the main tesamorelin peak. Vanguard Laboratory told the author that it sees this peak regularly in tesamorelin and counts it in its purity calculation, which gives a lower figure. The author reads the gap as a difference in how that peak was integrated. Whether a lab counts such a peak as an impurity is an integration choice.

This is one published case. It does not show which figure is right. It does show that a tesamorelin purity figure means little without the chromatogram and peak table behind it. Our guides to HPLC purity and Janoshik vs Freedom Diagnostics cover the method side.

How a lab confirms tesamorelin identity

Tesamorelin’s first 29 amino acids are the same as sermorelin’s. Sermorelin is GHRH(1-29) amide, with no hexenoyl group and no residues 30 to 44. Its calculated monoisotopic mass is 3355.8187 Da, about 1,777 Da below tesamorelin’s. CJC-1295 without DAC, which Janoshik’s test list also calls Mod GRF (1-29), is another analogue of the same 29-residue stretch.

LC-MS tells these peptides apart at once, because their masses are far apart. Retention time alone is weaker evidence. ICH Q6A says identification by a single retention time is not regarded as specific. Related peptides can elute close together, and a UV peak at the expected time says nothing about mass. The CJC-1295 testing guide and the guide to LC-MS identity go further.

How tesamorelin samples fail

A full report shows each kind of failure on its own line.

• Wrong peptide. The observed mass does not match 5132.7166 Da. A mass near 3356 Da would match sermorelin.
• mg far from the label. The basis decides the number. PubChem lists a tesamorelin acetate salt. Counter-ion and water add weight to the powder without adding peptide, so a result on total powder reads higher than one on peptide alone. Ask which basis the lab reports.
• Purity under a threshold. Small peaks next to the main peak decide whether a sample clears 99.5%, as the case above shows.
• Degradation. Tesamorelin contains one methionine (position 27), two asparagines and five glutamines. Bachem’s handling guide says peptides that contain Asn, Gln, Met, Cys or Trp have limited shelf lives, and it advises against long-term storage in solution. Oxidation of the methionine adds 16 Da and shows as a new HPLC peak. Deamidation adds about 1 Da, inside the isotope pattern, so it shows mainly as a peak close to the main peak. The guide to peptide degradation covers storage and shipping.

Labs that list tesamorelin, and blends

Lab	What its menu lists (checked September 2026)
Janoshik	Tesamorelin and sermorelin as single tests
Chromate	Tesamorelin and sermorelin as single tests
BTLabs	Tesamorelin on its extended compound list
Krause Analytical	Tesamorelin, sermorelin, and an ipamorelin and tesamorelin blend

Tesamorelin is also sold blended with ipamorelin. A blend report needs identity and mg for each peptide; the guide to peptide blend testing explains why.

How to read tesamorelin test results

1. Identity: expected mass 5132.7166 Da, the observed mass and the error in ppm, with several charge states that agree.
2. Purity: % area at a stated wavelength, with the chromatogram and peak table, so you can see what was counted next to the main peak.
3. Content: mg per vial, the basis, the reference standard, the uncertainty, and the % of the label claim.
4. Safety tests, if ordered: endotoxin as a number in EU/mg and EU/vial; sterility named as the 14-day USP <71> test.
5. The sample: the lot number and a photo of the vial as received.

A test shows what was in the vial the lab received. It does not say whether a product is safe to use.

How to get tesamorelin tested

Request a quote with the product form and the tests you want. Sterility needs its own unopened vials. Ship the vials sealed and numbered, and keep a photo of the lot number. For a group test, take vials from different kits so the result shows how much they vary.

What HK Analytical does for tesamorelin

We test tesamorelin as one sample with any mix of identity (LC-MS), purity (HPLC), content per vial, endotoxin (LAL), Sterility (USP <71>, 14 days), residual solvents, counter-ion (TFA, acetate), water content (Karl Fischer) and vial-to-vial consistency. We do not offer per-component blend analysis. Results within days of receipt. Sterility (USP <71>, 14 days) is the one test that takes 14 days, because the method incubates for 14 days. Every number comes with its raw data, including the chromatogram behind the purity figure. Each report is a signed record you can check at hkanalytical.com/verify, and it shows our photo of the vial as received. See the example report or request a quote.