Study

What 1,847 lab certificates say about peptide vial overfill

We compared the labeled mg against the lab-measured mg on every certificate in our registry that reports both. The label was wrong 99% of the time, and it was wrong in one direction.

We pulled every certificate in our registry reporting both a labeled mg and a lab-measured mg. Disclosure up front: goodtides is a peptide brand. Our own store is currently closed, and this registry aggregates certificates from 69 vendors — the overwhelming majority of them companies we have never sold. We have published the methodology and the underlying data so the numbers can be checked independently. The study set: 1,847 certificates, 69 vendors, tested between February 2024 and July 2026 by roughly 15 independent labs — Janoshik Analytical, ILS Labs, Kovera Labs, Freedom Diagnostics, Ethos Analytics and others.

Almost none of them contained what the label said.

1,564 of 1,847 vials measured ABOVE label — 84.7%

265 measured BELOW label — 14.3%

Median vial holds 6.9% more than the label claims

goodtides COA registry, computed 5 August 2026

Eighteen certificates — one percent — landed exactly on label. Everything else missed, and it missed in one direction far more often than the other.

The shape of the miss

Ratios are measured mg divided by labeled mg, so 1.069 means 6.9% more than claimed.

5th percentile: 0.923 — one vial in twenty holds 92% of label or less
25th percentile: 1.026
Median: 1.069
75th percentile: 1.152
95th percentile: 1.308 — the fullest vials hold about 131% of label

Two numbers matter most. 39.6% of vials hold more than 10% over label, and 6.8% hold less than 95% of label. The common failure is a vial meaningfully fuller than you think; the uncommon one is emptier.

Purity is not the problem

This is the part that surprised us. Of the more than 2,400 certificates on file, nearly 2,200 report a purity figure. The median is 99.74%. Only 0.7% come in below 98%.

Purity and mass answer different questions. Purity asks how much of the peptide in the vial is the right molecule. Mass asks how many milligrams are in there at all. The first question is largely settled; the second is wide open. Most people check a certificate to confirm the compound is real — but the more useful line is the measured mass, because that is what your dose is built on.

By compound

Compounds with 25 or more certificates. These ten are a little over half the study set.

Retatrutide — n=220, 90% over label, median 8.1% over
Tirzepatide — n=169, 93% over label, median 7.7% over
BPC-157 — n=115, 83% over label, median 7.5% over
MOTS-C — n=88, 84% over label, median 6.1% over
Tesamorelin — n=86, 94% over label, median 8.2% over
GHK-Cu — n=79, 70% over label, median 4.9% over
TB-500 — n=59, 92% over label, median 9.7% over
Semaglutide — n=52, 94% over label, median 13.0% over
Ipamorelin — n=49, 73% over label, median 5.7% over
NAD+ — n=45, 82% over label, median 4.4% over

Nothing here runs lean on average. GHK-Cu and Ipamorelin sit tightest to label; Semaglutide is the loosest.

Why vials are overfilled

Most of this is not vendors cheating. Three real mechanisms stack.

1. Deliberate fill overage is standard practice

You cannot get 100% of a vial's contents into a syringe. Liquid clings to the walls and stopper; some stays in the needle. Manufacturers fill above the labeled amount on purpose so a full labeled dose can still be withdrawn.

There is a mainstream-pharma analogue, though it cuts both ways. FDA's guidance on allowable excess volume points manufacturers to the recommended excess volumes in USP General Chapter <1151> — which are small, roughly 1-5% by container size — and asks them to justify any fill that exceeds them. The guidance exists to limit overfill, not to license it. Note the scope: that convention governs liquid fill volume, not lyophilized powder mass. But the same physics drives powder fills, and overfill targets are routinely built into lyophilized products so the full labeled amount can be recovered.

2. "10 mg of powder" is not "10 mg of peptide"

A lyophilized peptide is not pure peptide by weight. Synthetic peptides purified by HPLC usually come out as trifluoroacetate (TFA) salts, and that counterion is part of the mass you weigh. Net peptide content — the fraction of dry weight that is actually peptide — commonly runs 50-90%, with counterions, residual water and adsorbed solvents making up the rest. Well-processed lyophilized product typically carries another 1-3% moisture.

Theoretical net peptide content is MW / (MW + n × 114), where n is the number of TFA counterions needed to neutralize the peptide and 114 is TFA's molecular weight. A 1,000 Da peptide binding two TFA molecules is only about 81% peptide by weight. A 2025 paper in Pharmaceuticals measured roughly 25% TFA by weight in freshly purified angiotensin peptide samples.

So a certificate reporting 10.7 mg of gross powder against a 10 mg label may describe a vial that is dead-on for peptide — or one that is genuinely overfilled. It depends on whether the lab measured gross mass or net content, and certificates are not consistent about which they report.

3. Filling tolerance

Fill weight accuracy is a known hard problem in aseptic manufacturing, and research-use production is not held to pharmaceutical process controls. Scatter is expected. What the registry shows is that the scatter is not centered on the label — it sits above it.

What this does to your dose

If you dose off the label and your vial is 7% over, every dose is 7% larger than you intend. Not once — every time, for the life of the vial.

Reconstitution does not change how much peptide is in the vial. It only sets the concentration, which is mass divided by the water you add.

concentration (mg/mL) = vial mg ÷ mL of water added

units to draw = (target mg ÷ concentration) × 100

on a U-100 insulin syringe, 100 units = 1 mL

Example

A vial labeled 10 mg. The COA for its batch measured 10.7 mg. You add 2 mL of bacteriostatic water and want a 2 mg dose.

Off the label: you assume 10 ÷ 2 = 5 mg/mL, so 2 mg is 0.4 mL — 40 units. But the real concentration is 10.7 ÷ 2 = 5.35 mg/mL, so those 40 units deliver 2.14 mg. You are 7% over target, every dose.

Off the measured number: 2 ÷ 5.35 = 0.374 mL — 37 units, the nearest markable line. That delivers 1.98 mg, within 1% of target.

Three units on the barrel. That is the whole difference, and it is invisible unless you look up the certificate.

Run the tails. A vial at the 95th percentile — 13.1 mg under a 10 mg label — makes every label-based dose 31% larger than intended. One at the 5th percentile, 9.2 mg, makes it 8% smaller: 40 units delivers 1.84 mg. Both are real vials in this dataset.

There is a partial upside. Some of that extra mass is the deliberate holdup allowance — it exists to make the labeled amount withdrawable, and it stays behind on the vial walls and in the needle. Whatever is left over beyond that is extra peptide, but plan on roughly the labeled number of doses, not a bonus one. If you don't, it is an unplanned dose increase. Our dose calculator takes measured mg directly, so you can enter what the lab found instead of what the box says.

What this dataset cannot tell you

It is not a random sample. These certificates were supplied by vendors and labs. We collected them; we did not commission them or pull vials off shelves.
Selection bias runs one direction. Vendors who publish COAs at all are probably more careful than vendors who don't. If anything, this dataset flatters the market.
A certificate covers a batch, not your vial. One vial from a lot was tested. Yours came off the same fill line — meaningful evidence, but not a measurement of the thing in your hand.
Gross versus net is inconsistent. Some certificates report total powder mass, some report net peptide content, and they are not always clearly labeled. Part of the measured overfill here is counterion and water, not extra peptide.

That last point cuts against our own headline, which is why it belongs here. The defensible version: the mass in a peptide vial is reliably not the mass on the label, and the direction is reliably up. How much is genuine extra peptide varies by certificate.

What to actually do

Stop treating the label as a measurement. It is a nominal figure, and the registry says it is wrong 99% of the time.

Find the certificate for your batch — the lot number on your vial matched to a COA, not just a COA for that product. Our published lab results cover more than 2,400 certificates, and the underlying registry is available as machine-readable JSON at /api/coa-registry. If a vendor cannot produce one with a matching batch number, that absence is itself information.

Then dose off the measured number — but first check which number it is. If the certificate reports net peptide content, use it directly. If it reports gross powder mass, part of that figure is counterion salt and water rather than peptide, and dosing off it will run low. If the certificate does not say which it reports, treat it as gross and ask the vendor. If you track vials in the goodtides app, enter the tested mg when you log the vial and every unit calculation after that comes off the real figure.

The compounds discussed here are sold for research use and are not FDA-approved medicines. Nothing above is a recommendation to take any dose.

Registry

Search the lab results

Every certificate we hold, by compound and batch.

Free app

Dose off the measured mg

Link a vial to its certificate and the app does the math.

Frequently asked

Is an overfilled peptide vial a sign of a bad vendor?

Usually not. Deliberate fill overage is standard practice across injectable manufacturing, because you cannot withdraw 100% of a vial's contents. Some of the measured excess is also counterion salt and residual water rather than extra peptide. A vial that comes in well under label is the more unusual result.

Why does a certificate say 10.7 mg when the label says 10 mg?

Three reasons stack: intentional overfill so a full labeled dose can be withdrawn, the fact that dry peptide powder includes TFA counterions and residual water in its weight, and ordinary fill-weight variation. Whether the 10.7 mg is gross powder or net peptide depends on which test the lab ran.

Does purity tell me how many milligrams are in my vial?

No. Purity measures what fraction of the peptide present is the correct molecule, not how much total mass is in the vial. In our registry the median purity is 99.74% while the median vial still holds 6.9% more mass than its label claims. They are separate numbers on the certificate.

Should I recalculate my dose using the measured mg instead of the label?

Researchers working from certificates generally use the lab-measured mass, since that is what determines the actual concentration after reconstitution. Dosing off a label that is 7% high makes every draw 7% larger than intended. This is a description of practice, not medical advice.

A certificate exists for my product but not my batch number. Does it count?

It is weaker evidence. A certificate documents one tested vial from one lot. A COA for a different batch tells you the vendor can produce acceptable material, but not what is in the vial you are holding. Matching lot numbers is the standard worth asking for.

How was this analysis run?

We queried the goodtides COA registry on 5 August 2026 for every certificate reporting both a labeled mg and a lab-measured mg, then computed the ratio of measured to labeled for each. That gave 1,847 certificates across 69 vendors, tested by roughly 15 independent labs between February 2024 and July 2026.

Sources

For research peptide users tracking their own protocol. Not medical advice. Peptides referenced here are research chemicals, not FDA-approved drugs. Consult a qualified clinician for medical decisions.