Endotoxins, Purity vs Sterility
Purity, sterility and endotoxin are three different questions about an injectable product. A purity figure does not show it is sterile or endotoxin-free; here is what each measures.
Content last updated . This page has not been medically reviewed.
Urgent guidance first
Fever, chills, a racing heart, faintness or confusion soon after an injection can signal a serious reaction or infection. Anaphylaxis and sepsis are emergencies. In the United States, call 911 (elsewhere, your local emergency number). [1][2] This page is education only. It does not explain how to test, prepare or use any product, and nothing here lets a person confirm at home that an injectable is safe.The short answer
A purity certificate does not establish sterility. Purity, sterility and endotoxin content answer three separate questions, and a product can look acceptable on one and fail another.In other words, killing bacteria is not the same as removing what they leave behind, and a chemistry result does not say whether either is present.
What one real test-purchase study found
Researchers purchased semaglutide vials from illegal online pharmacies and analyzed them with several different tests. [7]- All delivered vials were considered probable substandard or falsified, based on visual inspection of packaging. [7]
- The lyophilized (freeze-dried) samples had no viable microorganisms at the time of testing, so the sterility-type result looked acceptable. [7]
- Endotoxin was nevertheless detected in all samples, at 2.1645 to 8.9511 EU/mg. [7]
- Measured semaglutide purity was 7.7% to 14.37%, against 99% claimed on the labels. The semaglutide content also exceeded labeled amounts by 28.56% to 38.69%, with no peptide-like impurities identified; the abstract reports these findings together without explaining how they relate. [7]
This study is about semaglutide from illegal sellers, not about the peptides marketed as "research" compounds, and it involved a very small number of vials. It does not tell you how any particular product performs. What it does show is that a clean result on one test can sit beside a failure on another, and that quality claims on a label were not reliable in these purchases.
Impurities and the immune system
Impurities in synthetic peptide products can trigger unwanted immune responses, according to a 2023 review. [3] A higher purity figure is therefore not irrelevant, but it still does not answer the sterility or endotoxin questions. See allergic reactions and immunogenicity.Related guides
Frequently asked questions
Does a high purity result mean an injectable is sterile?
No. In the semaglutide purchase study, sterility-type, endotoxin and purity results were separate findings. [7]
What is an endotoxin?
A component of the outer membrane of Gram-negative bacteria that acts as a fever-causing pyrogen when introduced into the bloodstream. [5]
Does sterilization remove endotoxins?
A review states pyrogens are not eliminated by standard sterilization processes. [6]
Can I check an injectable at home?
This library does not offer a home check, because no appearance test shows sterility or endotoxin content. FDA's guidance describes laboratory testing for finished products. [8]
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
How to read the evidence labels
Labels used on this page: approved medicine, evidence of harm, insufficient evidence and marketing claim.
Three questions, three kinds of test
| Term | Plain meaning | Why it matters |
|---|---|---|
| Purity | How much of the material is the intended molecule rather than something else | Impurities can provoke immune reactions [3] |
| Sterility | Whether living microorganisms are absent | Microbes in an injectable can cause infection [4] |
| Endotoxin | Fragments from the outer wall of certain bacteria that can cause fever | Can cause fever and, in severe cases, shock [5][6] |
Endotoxin, also called lipopolysaccharide (LPS), is found in the outer membrane of Gram-negative bacteria and is a pyrogen, a fever-causing substance, when introduced intravenously. [5] Pyrogens, both endotoxins and others, are not eliminated by standard sterilization processes and are biologically active once in the bloodstream, causing risks from mild reactions such as fever to septic shock and death. [6] Because of that, tests for sterility are essential for medical products and pyrogen testing is mandatory for injectable formulations. [6]
How regulated products handle this
References
- MedlinePlus, U.S. National Library of Medicine. Anaphylaxis. Read 2026-10-22.
- MedlinePlus, U.S. National Library of Medicine. Sepsis. Read 2026-10-22.
- Immunogenicity risk assessment of synthetic peptide drugs and their impurities. Drug Discov Today 2023. Read 2026-10-22.
- U.S. Food and Drug Administration. FDA warning letter to an online seller of unapproved drugs, reference 696885, February 26, 2025. Read 2026-10-22.
- Endotoxin detection: from limulus amebocyte lysate to recombinant factor C. Subcell Biochem 2010. Read 2026-10-22.
- More than 70 years of pyrogen detection: current state and future perspectives. Altern Lab Anim 2016. Read 2026-10-22.
- Multifactor Quality and Safety Analysis of Semaglutide Products Sold by Online Sellers Without a Prescription. J Med Internet Res 2024. Read 2026-10-22.
- U.S. Food and Drug Administration. Pyrogen and Endotoxins Testing: Questions and Answers (guidance). (content current as of 03/18/2026). Read 2026-10-22.
- U.S. Food and Drug Administration. Sterile Drug Products Produced by Aseptic Processing: Current Good Manufacturing Practice (guidance). Read 2026-10-22.
- U.S. Food and Drug Administration. Understanding the Risks of Compounded Drugs. (content current as of 06/22/2026). Read 2026-10-22.