Two Vials of Tirzepatide Got Lost in the Mail for Two Years. Here's What the Data Showed.

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View this post on the web at https://derekpruski.substack.com/p/two-vials-of-tirzepatide-got-lost

A real-world stability test nobody planned for
Peptide Crafters recently sent me a story I couldn’t pass up.
Back in June 2024, they shipped an order containing two vials of tirzepatide. The package never made it. UPS lost it somewhere in the system, and for the next two years it bounced between warehouses marked “destination unknown” — until one day, almost exactly two years later, it was returned to sender.
No temperature control. No insulation. No light protection. Two vials of lyophilized peptide sitting in random shipping facilities through two summers and two winters.
They sent both vials for re-analysis. The results genuinely surprised me.
The numbers
Baseline (June 2024, Prime Analytical Labs):
Net peptide content: 12.34 mg
Purity: 100.00%
Re-test (May 2026, Janoshik — both vials tested independently):
Net peptide content: 12.60 mg and 12.20 mg
Purity: 98.52% and 98.37%
If you want to verify the raw data yourself:
Baseline 2024 PAL report [ https://substack.com/redirect/0ca1ebb5-2ebf-47cc-b56d-01ae7281b8b6?j=eyJ1IjoiNGl3b2U2In0.sVDxRtmZ85v8kfdamY0krRXGMy3p768BWtuZifRB-Zs ]
Janoshik HPLC re-test [ https://substack.com/redirect/39cba4f1-b464-4366-af71-0fd08b2ee9ac?j=eyJ1IjoiNGl3b2U2In0.sVDxRtmZ85v8kfdamY0krRXGMy3p768BWtuZifRB-Zs ]
Janoshik LCMS raw data — vial 1 [ https://substack.com/redirect/4329d454-d17c-45f1-ad15-cca93ab51993?j=eyJ1IjoiNGl3b2U2In0.sVDxRtmZ85v8kfdamY0krRXGMy3p768BWtuZifRB-Zs ]
Janoshik LCMS raw data — vial 2 [ https://substack.com/redirect/97b85a47-d524-4d1a-8399-1a51d6edcc27?j=eyJ1IjoiNGl3b2U2In0.sVDxRtmZ85v8kfdamY0krRXGMy3p768BWtuZifRB-Zs ]
What the content numbers tell us
The net peptide content barely moved.
Both vials came back essentially identical to the original 12.34 mg baseline. The 12.20–12.60 mg spread between the two vials is well within normal analytical variance — that’s the kind of difference you’d see between any two labs running the same sample on the same day.
In other words: no meaningful content loss.
What the purity numbers tell us
This is where it gets more interesting.
The original 100.00% purity reading from 2024 is almost certainly overstated.
Testing methodology in 2024 wasn’t where it is today, and in my experience the lab that ran the original test (PAL) tended to come in higher on purity than other labs analyzing the same material. A more realistic baseline is probably 99.7% to 99.8%.
Even if we take the headline 100% at face value, we’re looking at roughly 1.5% purity loss over two years of completely uncontrolled shipping conditions. Adjusting for the likely overstatement, real degradation is closer to 1.2%.
There’s a second piece of validation worth pointing out: both vials came back within a tenth of a percent of each other (98.52% and 98.37%). That’s not a one-off reading. Two separate vials, exposed to the same wandering shipping conditions, landed in the same purity range. That’s reproducibility.
Why this challenges the conventional wisdom
A lot of the peptide community operates on the assumption that lyophilized peptides are extremely fragile outside of cold chain.
This data suggests otherwise.
Lyophilization works. Removing water from the equation is genuinely protective, and the activation energy required to drive meaningful degradation in a dry powder is substantially higher than in solution. These vials sat through two full summers in non-climate-controlled trucks and warehouses, and came back at 98%+ purity.
A few important caveats before anyone runs with this:
Don’t leave vials on a hot porch all summer just because this story exists.
Reconstituted material is a completely different stability question — once it’s in solution, the rules change entirely.
But for shipping windows of days or even weeks at ambient temperature? This kind of data should make people sleep easier.
What’s next
Peptide Crafters is planning to run an LCMS baseline on a fresh batch of tirzepatide so we can compare side-by-side using the same lab and same methodology. That removes the lab-swap variable entirely and gives us a much cleaner picture of true degradation.
I’ll share the follow-up data when it comes in.
In the meantime, this is exactly the kind of real-world stability evidence the space needs more of. Marketing claims and theoretical degradation curves are one thing. Two vials that survived two years of warehouse purgatory and came back at 98%+ purity is data.
— Derek
Strictly research use only. Not for human consumption.

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