Endotoxins are bacterial cell-wall components (lipopolysaccharides) that can cause fever, sepsis-like reactions, and inflammation if injected. Pharmaceutical-grade injectable peptides should have endotoxin levels below 0.5 EU/mg (endotoxin units per milligram). A real COA includes an endotoxin reading; vials lacking this test are higher risk. Endotoxin is the silent danger in poorly-manufactured peptides — purity might pass HPLC but a high endotoxin load can still hurt you.
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