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)