Tirzepatide test results: what 788 lab-tested vials show

Tirzepatide is the single most tested compound in our database, by a wide margin. Of the 1,529 vials we've logged across 67 vendors, 788 of them are tirzepatide. No other compound comes close; retatrutide, the next most tested, has 341.

That volume is itself a finding worth sitting with before getting into the numbers. It means the tirzepatide picture below rests on a far larger sample than almost anything else on this site, and it means a lot of buyers, independently, decided this was the compound worth the cost of a lab report. This article is a dated snapshot of what the 788 lab-commissioned tests on file as of September 28, 2026 show — for the current, continuously updated numbers, the tirzepatide results page is always live. Everything here concerns research tirzepatide sold for research use only; nothing in it is about dosing or use, because that's not something a lab report can tell you.

Why tirzepatide gets tested so much

Tirzepatide is a dual GIP/GLP-1 receptor agonist, developed and sold by Eli Lilly as Mounjaro, which FDA approved on May 13, 2022 for type 2 diabetes, and Zepbound, approved on November 8, 2023 for chronic weight management. That branded demand is likely a big part of why the research-market version is tested so heavily too: it's the compound with by far the largest number of people looking for it, and where there's that much buyer interest, there's also that much buyer anxiety about whether a given vial is real. A market this size also draws more first-time buyers, more group tests, and more people posting lab reports simply because there are more transactions happening in the first place.

The headline numbers

Across 788 tirzepatide vials in our data, as of September 28, 2026: purity is excellent, and almost every failure in the dataset comes down to quantity, not identity or purity. That's the shape of the story before you look at a single table.

Failures — a vial that's empty, under 95% purity, more than 20% under its labeled amount, or more than 50% over it — sit at 15 of 788, or 1.9%. Twelve of those fifteen are quantity failures under label (including two empty or near-empty vials), and three are quantity failures over label. Zero are purity failures. Whatever else this data shows, it isn't a story about fake or wildly impure tirzepatide; it's a story about vials not always holding the amount printed on the label.

Purity: about as clean as this market gets

Of 785 tirzepatide vials with a purity result, 710 (90%) came in at 99% or higher, and 602 (77%) at 99.5% or higher. Median purity across all of them is 99.76%. Not a single vial in our data tested under 95% purity — the purity-failure threshold on our site.

That's a notably cleaner picture than some other compounds we track. Tesamorelin, for comparison, has a median purity of 99.27% and one vial under 95%.

Dose vs. label: the real story is fill amount, not purity

Purity tells you what share of the material in a vial is tirzepatide. It says nothing about how much tirzepatide is actually in there. That's a separate measurement — quantity, or content, tested against what the label claims — and it's where almost all of tirzepatide's failures live.

Of 764 vials with a measured amount, the median result is +5.4% over label. Here's how the tail ends of that distribution break down:

And here's the middle of the distribution, where most vials actually sit: 309 vials, 40%, land within ±5% of label, and 519, 68%, land within ±10%.

Read plainly: 4 in 10 vials land within ±5% of label, and about two-thirds land within ±10%. At the tails, more vials run over label than under it — 51 vials more than 20% over versus 12 more than 20% under — which matches a pattern we see across this market generally: overfill happens more often than underfill, though neither is rare enough to ignore.

The vial-size finding: 60 mg vials measure much closer to label

This is the single most useful thing the tirzepatide data shows, and it isn't visible at all in the market-wide median. Break the same 764 vials out by their labeled vial size, and the spread is dramatic:

At the 15 mg vial size, only 7 of 43 measured vials — about 1 in 6 — landed within ±5% of label, with a median running +12.5% over. At the 60 mg vial size, 147 of 251 — 59%, close to 6 in 10 — landed within ±5%, with a median of just +1.7%. That's not a small gap. A 60 mg vial in our data is, on the whole, more than three times as likely to land near its printed label than a 15 mg vial is, and its typical overfill is roughly a seventh the size.

We don't have a confirmed reason for this from the reports themselves — a lab report tells you what a vial measured, not why a manufacturer's fill process behaves differently at different concentrations. It isn't a simple bigger-is-better line either: 40 mg vials ran further over label than 30 mg vials did. Whatever the mechanism, the practical takeaway from the data is plain: vial size is one of the more informative things to notice on a report, and it's worth checking that the label amount you're comparing a result against matches the vial size actually being described.

Overfill has been drifting up, year over year

Tirzepatide also shows a clear trend over time. Grouping by the year each test was conducted:

(2023 has a single vial on record and isn't meaningful as a group.) The median has climbed from +3.8% over label in 2024 to +7.3% in 2026, and the share landing within ±5% has fallen from 48% to 32% over the same stretch. It shows up across hundreds of vials each year, though we haven't broken the drift down by vendor, so we can't say how evenly it's spread across sellers.

We can't say from this data alone whether that's buyers ordering different vial sizes over time (which the vial-size table above suggests would move the average), manufacturers shifting fill targets, or some mix of both. What we can say is that "closer to label" has gotten less common with each passing year in our data, not more.

Vendors: how the spread looks without naming names

We don't name individual vendors in articles — that's what the live vendor ratings are for, where scores update as new reports come in and every claim is tied to a specific, checkable report. Here's how the ranked vendors look right now for tirzepatide specifically:

A ranking here isn't automatically a green light — the table also flags any vendor with more than 5% failed vials, and a vendor needs at least five separate tirzepatide lab reports before it's ranked at all. But the shape of the wider spread is worth describing too.

Of the 48 vendors with tirzepatide results in our data, 15 have only a single vial tested, and 21 have five or more vials. Fifteen vendors are currently ranked for tirzepatide specifically; ranking takes at least five separate lab reports, not just five vials. Thirty-eight of the 48 vendors have zero failed tirzepatide vials on file; the fifteen failed vials in the dataset are spread across ten vendors, with no more than three failures sitting at any single one. Among the fifteen ranked vendors, nine have a 0% tirzepatide failure rate, and their scores for this compound range from 79.1 to 95.6, with a median of 88.7. Two ranked vendors currently sit below the tirzepatide market average.

The pattern that stands out isn't a handful of bad actors driving all the failures — it's that failures, where they exist, are distributed fairly widely and thinly, while a solid majority of tested vendors have a clean record so far. That can change with more data; a vendor with only five or six reports on file is one bad result away from a very different-looking record.

Endotoxin: results cluster in the middle, not the extremes

Sixty-four of the 202 endotoxin results in our overall database are tirzepatide. Twelve came back below the lab's detection limit, and two were reported simply as "Pass" — a smaller share of clean, below-limit results than we see for retatrutide, where 24 of 61 results (about 39%) came in below the limit versus 12 of 64 (19%) here. The rest of the tirzepatide results skew toward the middle of the range rather than either extreme: 5 under 2 EU, 19 at 2–10 EU, 9 at 10–20 EU, 8 at 20–100 EU, 4 at 100 EU or more (the highest a single result of 2,306 EU, with no basis stated for whether that's per vial or per milligram), and 5 more reported only as ">10 EU," a threshold rather than a precise number.

Put differently: most numeric tirzepatide endotoxin results in our data sit in the 2–20 EU band, rather than clustering down near zero the way retatrutide's results tend to. We're not assigning a "safe" or "unsafe" label to any of these numbers — pharmacopeial endotoxin limits are set for approved drug products administered under specific, regulated conditions, and they don't transfer cleanly to a research vial of unknown provenance. This is what independent lab reports measured, not a judgment about what any level means for anyone.

It's also worth repeating a caveat that applies to endotoxin testing across this entire market: these are the vials buyers chose to send in for endotoxin testing, not a random sample of everything sold. That skews the picture in a direction we can't fully quantify, likely toward buyers who already had some reason for concern.

Sterility: a small, heavily caveated sample, and all six failed

Only six tirzepatide samples in our data have been tested for sterility — reported as TAMC and TYMC, total aerobic microbial count and total yeast and mold count. All six failed at least one of the two counts. That matches what we see across the tirzepatide/retatrutide group broadly: every one of the sterility samples from either compound in our database failed at least one count.

We want to be careful about what that does and doesn't mean. Six samples is a very small number, drawn from buyers who were likely already suspicious enough to pay for a sterility test in the first place — that's a selection effect, not a random cross-section. A failed microbial count on a sample prepared for lab testing is a lab finding about that specific sample; it is not a medical diagnosis, and we're not making any claim about what it means for anyone's health. We report it because it's real data from real tests, and because a reader asking "has anyone tested this for sterility" deserves an honest answer about how thin that data actually is.

TFA and other tests: mostly clean, mostly rare

Twenty tirzepatide results in our data include a TFA (trifluoroacetic acid) test, and nearly all of them read "0" or "not detected." Two reported 1.4 micrograms each; one report noted this was possibly a remnant from incomplete post-manufacturing ion exchange, a routine purification step. Heavy metals and LC-MS impurity screens are rarer still for this compound — one heavy-metals result (not detected) and two LC-MS screens, both describing mannitol, tirzepatide, and degradation products. Mannitol is a common bulking agent in freeze-dried vials, so seeing it listed on an LC-MS screen is expected.

Research-grade tirzepatide vs. Mounjaro and Zepbound

This search comes up often enough to address directly, and the honest answer is about oversight, not chemistry speculation. Mounjaro and Zepbound are Eli Lilly's branded tirzepatide products, manufactured and released under FDA-regulated conditions: every batch goes through validated manufacturing processes, in-process controls, and release testing before it reaches a pharmacy, and the whole chain is subject to FDA inspection.

A research-market tirzepatide vial has none of that built in. Whatever quality assurance exists is whatever a specific buyer arranged and paid for after the fact — which is exactly what this article, and this site, are built around measuring. A lab report on a research vial tells you what that one sample measured on the day it was tested. It does not tell you what every vial from that batch contains, what the manufacturing process looked like, or whether any regulatory body has reviewed it. That's the actual difference: one is released under a system with built-in, mandatory checks; the other is checked, if at all, after the fact and at a buyer's own initiative. We're not making a claim here about which is more effective or what either should be used for — that's outside what any lab report, or this article, can answer.

What this data can't tell you

A lab report describes one vial, on one day, as measured by one lab. It doesn't tell you about a vial from a different batch, a different vendor claiming the same source, or the same vendor's product six months from now. Our vial-size and year-over-year breakdowns are patterns across hundreds of individual reports, and they're useful precisely because the sample is large — but "large" isn't "complete." We don't know the total size of the tirzepatide market these 788 vials were drawn from, and every number here reflects vials that someone specifically chose to test (almost always a buyer, occasionally the vendor itself), which almost certainly skews toward people who had some reason to check in the first place.

It's also worth restating what this data will never speak to: nothing here says anything about dosing, effects, or how any compound should be used. A lab report answers "what's actually in this vial," full stop.

What to check on a tirzepatide report specifically

Given everything above, a few things are worth looking for on any tirzepatide certificate:

• Vial size, and what it's being compared against. A quantity result only means something next to the label amount it's measured against — and given how differently 15 mg and 60 mg vials perform in our data, knowing the size matters more here than for most compounds.
• Test date. Given the year-over-year drift toward higher overfill, a two-year-old report says less about a current batch than a recent one would.
• Whether quantity was tested at all, separately from purity. Given that every tirzepatide failure in our data is a quantity issue and none are purity issues, purity alone won't tell you what you need to know.
• The lab and report key. Each result on a vendor's page shows which lab ran the test and, where the report includes one, its report key, so you can check the number against the lab's own record where that's possible.

We publish every tirzepatide result we can verify, matched against its vendor, on the tirzepatide results page, which updates as new reports come in — this article is a snapshot, that page is current. If you've had a tirzepatide vial tested and want to add it to the record, you can submit the report.

The database totals in the opening paragraph and the first two FAQ answers update automatically from VendorVerify's lab results; all other figures are a snapshot from the VendorVerify database as of September 28, 2026. See also how to read a peptide COA for what each line of a certificate measures, and underdosed peptides for how tirzepatide compares with other compounds on dose vs. label.