We tested peptide degradation so people can stop guessing
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This info is crazy helpful!!! I would love to know life span of lyophillized powder in the freezer. I can be a Preper and like to have plenty of stock, but always worry that I've bought too much...
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At Peptide Critic, we get asked this stuff constantly.
- I left my peptide out overnight, is it ruined?
- How long is reconstituted peptide actually good for?
- Does refrigeration really matter that much?
- Is bacteriostatic water helping or hurting stability?
Some of these are smart questions. Some are panic questions. Some are asked by people staring at a vial they forgot on the counter and hoping for good news.
Either way, the problem is the same: most people are working off vendor claims, forum lore, and random opinions repeated as fact.
So we decided to actually test it.
We partnered with Analytical Formulations Inc. (AFI) to evaluate the stability of three peptides after reconstitution:
- Tirzepatide
- MOTS-c
- Mazdutide
We wanted to see how much activity remained over time under refrigerated vs ambient storage conditions.
Also worth noting: every batch used for these tests passed endotoxin and sterility screening. Degradation is one issue. Contamination is another.
How the testing worked
Each peptide was tested in duplicate.
- One sample was stored at 36°F
- One sample was stored at ambient room temperature, roughly 75–80°F with an average around 76°F
All samples were:
- reconstituted with bacteriostatic water containing 0.9% benzyl alcohol
- stored in a light-free environment
Activity was tracked over about four months using UV-Vis spectrophotometry, looking at reduction in the extinction coefficient in the aromatic range.
Plain English version: we were measuring how much usable activity remained over time, not just whether a vial still looked normal.
Big picture takeaway
Refrigeration helped across the board. No shock there.
What was more interesting is that all three peptides seemed to follow a similar pattern:
- a slower decline early on
- then a much sharper drop later
So degradation did not look like a smooth straight line from Day 1 to the finish. It looked more like a threshold got crossed and things started falling apart faster.
That pattern showed up in refrigerated samples too, not just the room-temp ones. So temperature is clearly important, but it does not look like it is the only thing driving long-term loss once peptides are reconstituted.
Tirzepatide results
Tirzepatide was more resilient on the counter than a lot of people would expect.
Ambient (~76°F)
- Day 7: 97.8%
- Day 15: 95.0%
- Day 31: 40.3%
Refrigerated (36°F)
- Day 15: 94.1%
- Day 61: 92.3%
- Day 113: 40.1%
So no, leaving Tirzepatide out briefly does not appear to mean instant death.
But the drop between 2 weeks and 1 month at room temperature was brutal. That is the important part. Short-term resilience is not the same thing as long-term stability.
MOTS-c results
This one mattered because MOTS-c has been surrounded by a lot of exaggerated claims, especially the idea that it breaks down after just a few hours.
Our data did not support that.
Ambient (~76°F)
- Day 7: 86.1%
- Day 15: 76.2%
- Day 31: 16.9%
Refrigerated (36°F)
- Day 15: 96.0%
- Day 31: 88.9%
- Day 113: 35.4%
So yes, this pretty clearly debunks the “MOTS-c dies in hours” narrative.
That said, it was not magically stable forever either. At room temp it fell off hard by Day 31, and even refrigerated long-term retention dropped substantially by Day 113.
Mazdutide results
Mazdutide ended up being the strongest room-temperature performer of the three in the earlier part of the study.
Ambient (~76°F)
- Day 7: 78.3%
- Day 15: 71.2%
- Day 31: 64.5%
Refrigerated (36°F)
- Day 15: 93.4%
- Day 61: 88.5%
- Day 113: 38.3%
So while refrigeration still gave the best overall retention, Mazdutide looked the most forgiving on the counter early on.
What this means in real life
If your question is:
“I left my peptide out. Is it ruined?”
The answer is usually not as simple as yes or no.
Based on these results:
- some reconstituted peptides retain meaningful activity for a while even outside refrigeration
- different peptides behave very differently
- refrigeration still matters
- long-term decline can suddenly accelerate harder than people expect
That means “it survived overnight” and “it stores well long term” are not the same statement.
One interesting question this raises
All samples in this study were prepared using bacteriostatic water with 0.9% benzyl alcohol.
That raises an obvious follow-up question:
Is benzyl alcohol contributing to the threshold-like drop we observed later?
Maybe.
The pattern across all three compounds suggests that storage temperature is not the only variable affecting long-term stability after reconstitution. That does not make bacteriostatic water the villain, because sterility matters, but it does make it something worth looking at more closely in future testing.
Limitations
This was not meant to be the final word on every peptide and every formulation.
This was a controlled comparison using:
- three peptides
- one diluent type
- one ambient range
- one refrigerated condition
- one analytical method
Commercial products may behave differently depending on buffers, excipients, formulation choices, and manufacturing controls.
Still, this is a lot more useful than recycled forum arguments and vendor wishful thinking.
Bottom line
If you want the best retention:
- refrigerate reconstituted peptides
- do not drag out usage longer than necessary
- do not assume all compounds behave the same
- stop repeating that MOTS-c dies in hours
- stop assuming Tirzepatide instantly becomes trash if it sits out briefly
The bigger lesson here is that degradation is real, but it is not always immediate, linear, or intuitive.
That is exactly why we ran the tests.
We would rather test it than guess.
@Randy God's work
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@jborja compounding pharmacies put preservatives in their Tirz and other GLP-1’s, so it’s not unusual for them to have a BUD or extended BUD of a year after they were bottled. My current vial was expired when I received it and came with a note saying that it is good until June of this year.
I have received compounded tirz reconned with bac water (just tirz) and also with sterile water (included B12 and was pink.) Depends on the pharmacy and what they are doing, I guess.
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Lyophioized powder can sit in the freezer for a LONG time without degradation. I'm assuming these kits were new and directly from company?
Any future plans on doing this with older lyophilized powder that has been sitting in the freezer/fridge without reconstitution?
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Would you adjust your dose based on this data when using at 4 weeks, refrigerated tirz?
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I personally would not. Assuming there is variability among products and how people store things, I would consider this data to be useful and reassuring. But I wouldn’t assume that every batch and vial will have this exact consistent decay.
I guess you could bump up a unit or two, but I would be more wary of overdosing a GLP-1 than losing efficacy due to underdosing by .5-1mg.
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@matthewwalsh I inject cold all the time; I don’t care. I don’t think there is any more discomfort than at room temperature, or, again, I don’t care. If that is a concern, do what I do for my bride’s rat(she has concierge service!) and draw the syringe, letting that get to room temperature while the vial is back in the fridge.
Be wary using AI for this. It’s mostly scraping all the other web sites and posters, which are all either repeating one source(e.g. bac water goes bad after 28 days) or are aggregating made up stuff that isn’t verified.
I am not saying it isn’t useful, but I am using AI for work and it’s just great when you ask it to summarize regulatory requirements for financial derivatives and it makes up answers when it can’t find what you’re looking for.
@ResearchCat said in We tested peptide degradation so people can stop guessing:
@matthewwalsh I inject cold all the time; I don’t care. I don’t think there is any more discomfort than at room temperature, or, again, I don’t care. If that is a concern, do what I do for my bride’s rat(she has concierge service!) and draw the syringe, letting that get to room temperature while the vial is back in the fridge.
ResearchCat, when I read the top portion of your post above, I went from LMAO to almost hysterical laughter! I'm not making fun of anyone; I'm just an ignorant old lady (70), parents born before First World War, trying to learn something new here (overwhelming), and I've never used a pen in my life. So, I'm at the top of the page reading all the repetition, and got to the cold injection portion, over and over... Then, you came up with the simple answer that I'd been yelling at my laptop while reading it over and over; I don't know, it just hit the funny bone real hard. I love SIMPLE; I am SIMPLE. LMAO! Thank you for the humorous moments! (She said, as she wiped the tears from her eyes.)
@randy & Jeff: This is a great report and I know you put some real work into it. Very helpful to this old lady. Nothing like learning something completely new by starting with the facts.
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@eleanor I am glad I gave you a good chuckle. I tell people all the time: You might think I am a jerk, but I assure you that I am funny.
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I personally would not. Assuming there is variability among products and how people store things, I would consider this data to be useful and reassuring. But I wouldn’t assume that every batch and vial will have this exact consistent decay.
I guess you could bump up a unit or two, but I would be more wary of overdosing a GLP-1 than losing efficacy due to underdosing by .5-1mg.
@ResearchCat thank you for answering.
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S Stan Douglas referenced this topic
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A afkar7 referenced this topic
