Possibly, if you don’t know the source.
Personally I’ve never had any issues. I inject a sample from every batch I receive 
even though the COAs indicate no endos and >98% purity (purity is not the same as an assay). The assay is just as important, that indicates how much of the active ingredient is in the total amount of powder being tested/sold.
With pure powder peps, you might have 90% to 98% active ingredient depending on the peptide
With lyophilized peps it would be more in the 20% active ingredient range
To me this means the “filler” in lyo. peps must also be as pure or more pure than active, as there is much more filler than active being injected.
Any peptide that has endotoxins will make you quite ill for a period of time, 2 to 4 hours. If your supply has endo’s it won’t be subtle you will know in 5 to 10 minutes. High levels could be fatal but I’ve never heard of that in the world of “research” peptides.
can endotoxins in peptides kill you, use only clin.pdf (361.0 KB)
Alarmist stuff as always with the endotoxins. The limit as defined by the FDA is 5 EU/kg/hour, which is quite high in practical terms, ie for a 70kg person, levels as high as 350 EU per dose, per hour are acceptable. In practice, most people don’t inject more than once a day anyway.
You can actually test for those. I’ve seen dozens of endotoxin reports, and in practice values <100 EU/vial are 80-90% of reported endotoxin levels per vial (note that this is per vial, so it would be much lower per mg).
Examples:
- vial of 20mg tirzepatide, total endotoxin 10 EU. Dosage is 5mg. Actual amount of endotoxin for your dose: 10/20*5 = 2.5 EU
- vial of 100mg tirzepatide, total endotoxin 50 EU. Dosage is 10mg. Then actual amount of endotoxins for your dose is: 50/100*10 = 5 EU.
Here is an example of a third party test we ran for a vial of 30mg tirzepatide:
https://janoshik.com/tests/73588-R30_Z9UD9TI4HYD6
The level was found to be 0.751 for the whole vial, or about 0.025 EU/mg