Underdosed peptides: how to read the mg result, and why overfilled vials fail too

Underdosed peptides: what the word means on a lab report

A peptide vial is underdosed when a lab measures less of the target peptide than the label claims. The shortfall must be larger than the result’s own margin and fall outside the window you judge it by. The number to read is content per vial: mg of the target peptide, measured against a reference standard and set against the label as a percentage. Three details decide whether a low number is a real shortfall: the basis of the mg, the uncertainty and the window. An overfilled vial comes from the same test with the opposite result, and several rating standards fail it too.

A content result has five parts. The example values are an illustration, not a test result.

Part of the result	Example	What to check
mg per vial	8.4 mg	That it was measured: a method, a reference standard and a test date
Basis	Free base	Free base (peptide only), salt form or whole powder
Uncertainty	± 0.4 mg (k = 2)	Whether the range reaches the label or a limit
Label claim	10 mg	Its source: the seller’s label; the lab does not measure it
% of label claim	84%	Worked out from the mg and the label claim

In our September 2026 review of public certificates from 25 labs and one rating site’s certificate format, 21 of 26 printed an mg result. Only 6 printed the % of label claim clearly, and only 1 clearly stated the basis. At least one printed the label claim in its quantity field, as if it had been measured.

Net peptide or whole powder: why a correct vial can read low

Labels rarely say what “10 mg” means. It can mean 10 mg of powder or 10 mg of peptide. A freeze-dried peptide is a salt that also holds some water. Bachem notes that research peptides are typically above 95% pure by HPLC, yet the peptide content of the solid may range from 70 to 90%. Counter-ions such as acetate or TFA and residual moisture make up the rest.

So a vial filled with 10 mg of powder can hold 7 to 9 mg of peptide. A lab that reports free base, the peptide alone, will print 70 to 90% of the label for that vial, and nothing is missing. A lab that weighs the whole powder, or reports the salt, will print more. The basis alone can move a result by 10 to 30% before any real underfill. Our guide to net peptide content works through the calculation. The counter-ion and water content tests show where the rest of the weight goes.

Fill windows: how far under the label counts as underdosed

A research peptide from a direct seller is not a licensed medicine, so no pharmacopoeia limit applies to its vial. Rating platforms set their own windows. Finnrick, a US platform that publishes test results, rates samples under five standards. Underfill and overfill both fail outside the window.

Standard or reference	Window vs label	Low end, 10 mg label	High end, 10 mg label
Finnrick Purity Focus (default) and Purity Focus Strict	±35%	6.5 mg	13.5 mg
Finnrick Standard	±25%	7.5 mg	12.5 mg
Finnrick Accuracy Focus	±20%	8.0 mg	12.0 mg
Finnrick Super Strict	±15%	8.5 mg	11.5 mg
Peptigrity “in line” band	95 to 110%	9.5 mg	11.0 mg
Oxytocin injection, International and British Pharmacopoeias	90.0 to 110.0%	9.0 mg	11.0 mg

The oxytocin row, from a 2020 review by Lambert and colleagues, shows the limit for a licensed peptide medicine.

Two points follow. First, the windows differ by more than a factor of two, so “underdosed” depends on the one you use. A vial at 80% of its label passes Finnrick’s default and fails Super Strict. Second, the default window is wide enough to absorb the basis problem above. A powder-filled vial that is 70 to 90% peptide stays inside ±35%. Under ±15%, any result below 85% fails, whatever the cause. Our guide to Finnrick covers its standards in full.

Why overfilled vials fail some standards

Vendors and users dispute Finnrick’s overfill rule. In a September 2026 interview on Krysia’s Substack, Finnrick’s CEO said he does not regret it. He sees overfill as evidence that a seller does not control its filling, and he does not plan to change the rule.

Peptigrity, which collects certificates, never colours a result above 110% of the label as good. Its methodology explains that it “cannot tell a gross-mass reading from a real overfill”, and it treats real overfill as a filling inconsistency. In September 2026, about 40% of single-compound certificates that report both figures were above 110%.

Medicine limits have an upper line too: the oxytocin limit above stops at 110.0%. The FDA lists too much active ingredient, as well as too little or none, among the problems with illegally sold GLP-1 drugs.

For a buyer, a high result means the label cannot be relied on. It may not mean more peptide, though: a whole-powder or salt result reads high by design, so check the basis first.

Same batch, different verdicts

Results on one batch can land on either side of a window, as two published comparisons show. The table converts each lab’s mg to % of the label and lists the Finnrick windows each result falls outside.

Batch and source	Lab	mg reported	% of label	Outside these windows
Retatrutide, 10 mg (Peptide Critic)	Vanguard	10.18, 10.30	101.8 to 103.0%	None
Retatrutide, 10 mg	Analytical Formulations	10.71, 10.85	107.1 to 108.5%	None
Retatrutide, 10 mg	Janoshik	11.03 to 11.49 (four results)	110.3 to 114.9%	None
Retatrutide, 10 mg	TrustPointe	12.296, 12.328	123.0 to 123.3%	±15%, ±20%
Retatrutide, 10 mg	Freedom Diagnostics	12.47, 12.80	124.7 to 128.0%	±15%, ±20%; one vial ±25%
Tirzepatide, 60 mg (Krysia’s Substack, 2 Aug 2026)	BTLabs	62.3	103.8%	None
Tirzepatide, 60 mg	Chromate	70.99, 71.63	118.3 to 119.4%	±15%
Tirzepatide, 60 mg	Accumark	73.72, 75.44	122.9 to 125.7%	±15%, ±20%; one vial ±25%

Under Finnrick’s default ±35%, every result passes. Under ±25%, each batch passes at most labs and fails on one vial at one lab. Under ±15%, both batches pass at some labs and fail at others. Under Peptigrity’s bands, only three labs’ results sit in the 95 to 110% range. The batches did not change between rows.

Each row is a single published case. It does not show which lab is right, and the true content of these vials is unknown. A reading above a window does not by itself mean a lab error: it can reflect the basis the lab reports, its reference standard or real overfill. Our guide on why labs disagree covers the causes. A fill verdict from one lab, close to a line, is weak evidence on its own.

How to tell if your vial is really underdosed

Work through these checks in order.

1. Confirm identity. A wrong peptide or an empty vial reads at or near zero for the target. Identity by LC-MS comes first.
2. Check that the mg was measured. Look for a method, a reference standard and a test date. A bare “10 mg” beside the label claim may be a copy of the label.
3. Find the basis. A free-base result at 70 to 90% of the label can be a correctly filled powder vial.
4. Read the range, not the point. Take an illustrative result of 6.7 ± 0.4 mg (k = 2) on a 10 mg label. The range, 6.3 to 7.1 mg, crosses Finnrick’s default line at 6.5 mg, so this result alone cannot settle pass or fail. Stated margins differ: in answers to Finnrick’s questionnaire, BTLabs gives ±2 to 3%, and Krause accepts its check standard within ±10%, which it treats as its floor for error. Our guide to measurement uncertainty explains ± and k.
5. Test more than one vial. One low vial may be a single short fill. Two or more vials picked at random, at one lab on one basis, show the mean and the spread. See how many vials to send.
6. Compare like with like. If a seller’s certificate and your own result disagree, check that both state the same basis before you call either one wrong.

Result as % of label	Usual reading
At or near zero	An identity problem: wrong peptide or no peptide
Under 65%	Outside every Finnrick window, and lower than salt and water usually explain
65 to 85%	Depends on basis and window: a free-base result here can come from a powder-filled vial
85 to 115%	Inside every Finnrick window, if the uncertainty range does not cross a line
Over 115%	Check the basis first, then consider real overfill

What HK Analytical reports

Our content per vial test reports the mg of the target peptide in the vial, as free base, measured against a reference standard, with the uncertainty and the % of the label claim. If no qualified reference standard exists, the value is marked “estimated”. Vial-to-vial consistency gives each vial’s mg with the mean, range and relative standard deviation. Identity (LC-MS), purity (HPLC), counter-ion and water content can go in the same order. Results within days of receipt. Every number comes with its raw data, and the report carries our photo of the vial as received, in a signed record you can check at hkanalytical.com/verify. The example report shows the layout, and a group test shares one order across buyers of the same batch.