https://ntp.niehs.nih.gov/go/glyphosate

Glyphosate & Glyphosate Formulations

Findings: Evaluation of the herbicide glyphosate, (aminomethyl)phosphonic acid, and glyphosate-based formulations for genotoxic activity using in vitro assays. Environ Mol Mutagen. 2023. (Data Tables available.) | Comparative investigation of the potential of glyphosate and glyphosate-based formulations to cause oxidative stress and DNA damage in human skin and liver cell systems. Toxicol Sci. 2026. (Data Tables available.)
Tractor going across crops

Research Overview

Status: Completed
Substances: Glyphosate
Nominated: June 2016

Background Information

Glyphosate, a chemical that controls weeds and grasses, is the most widely used herbicide worldwide. The major reason glyphosate is used so broadly is because many crops have been genetically engineered to be resistant to glyphosate, allowing it to target weeds while leaving resistant crops unaffected. When applied as a mixture with other substances, plants can more readily absorb glyphosate, making it more effective. People can be exposed to glyphosate when they use glyphosate-based formulations (GBFs) on their lawns, gardens, or for landscaping around their homes. It can get on a person’s skin, get in the eyes, or be brought into the body by breathing it in during use. Residual amounts of glyphosate can also get into a person’s body by ingestion of food or water. Individuals who regularly handle glyphosate products as part of their occupation have higher exposures.

Glyphosate was first nominated to the NTP for testing in 1981, before the development of glyphosate-resistant crops. NTP conducted a series of short-term studies including 13-week toxicity studies of glyphosate in feed, which were published in 1992. At that time, few toxicological effects were observed, and there was no evidence of genetic toxicity for endpoints of chromosomal damage (in vivo) or gene mutations (bacterial reverse mutation assay, also known as the Ames test).

In March 2015, the International Agency for Research on Cancer (IARC) classified glyphosate as "probably carcinogenic to humans" (Group 2A). This was based on "limited" evidence of cancer in humans from epidemiological studies of exposures to GBFs and "sufficient" evidence of cancer in experimental animals from studies of glyphosate alone. IARC also concluded that there was "strong" evidence for genotoxicity (DNA damage), a determination that was based on studies of both glyphosate and GBFs. Additionally, IARC concluded that there was "moderate" evidence for the genotoxicity of (aminomethyl)phosphonic acid (AMPA), a microbial metabolite of glyphosate. Some studies, which are publicly available, suggest that the human intestinal microbiome metabolizes glyphosate to AMPA. The IARC listing was one of the reasons NTP considered conducting further testing in 2016. Furthermore, IARC concluded that “Strong evidence exists that glyphosate, AMPA, and glyphosate-based formulations can induce oxidative stress.”
Back to Top

NTP Studies & Findings

Human exposure to glyphosate usually occurs in the form of glyphosate-based formulations (GBFs). Few studies have made side-by-side comparisons of the toxicity of glyphosate and GBFs using the same experimental methods. NTP compared the toxicity of both glyphosate and glyphosate formulations, using the same methods. Specifically, NTP study goals were to:

  • Evaluate whether glyphosate causes genotoxicity, or damage to DNA, using the bacterial reverse gene mutation assay (Ames test), an in vitro micronucleus assay to detect chromosomal damage, and a multiplexed DNA damage assay that distinguishes whether chromosomal damage is due to chromosome breaks or changes in chromosome number. These studies were conducted using human TK6 cells, a cell line that is recommended by the Organization for Economic Cooperation and Development for in vitro genetic toxicity assays.
  • Evaluate whether glyphosate induces oxidative stress, the harm that cells and tissues experience when overwhelmed with production of free radicals that can damage protein and DNA. These studies were conducted using several high-throughput screening assays with differentiated human liver cells and immortalized human skin cells.

The genetic toxicity studies and the high-throughput screening studies compare the effects of glyphosate versus GBFs on measures of genotoxicity, oxidative stress, and cell viability.

What did the studies find?

Genotoxicity Studies

Glyphosate and (aminomethyl)phosphonic acid (AMPA), a microbial metabolite of glyphosate, did not cause permanent changes to DNA, such as gene mutations or chromosomal damage. These kinds of changes to DNA are often associated with increased risk for cancer.

The highest concentration of glyphosate used in NTP’s human cell culture studies was comparable to an adult man drinking about 16 ounces of a representative glyphosate-based formulation that contains 41% glyphosate.

In NTP’s studies, some glyphosate-based formulations caused DNA damage. Because glyphosate itself did not cause DNA damage in the tests that were used, the DNA damage likely was caused by other components of the formulations. Herbicide product labels list active ingredients, like glyphosate, but other components of formulations are considered "inert" for regulatory purposes and are not reported due to confidential business information protection for companies that manufacture herbicides.

Overall, the findings from our genetic toxicity experiments indicate that it is unlikely that glyphosate could cause cancer through a genotoxic mechanism that permanently damages DNA. Our findings do not rule out that exposure to glyphosate might cause cancer through other mechanisms.

The findings are consistent with studies conducted by the NTP in 1992, which reported that rodents exposed to high levels of glyphosate in feed showed little evidence of toxicity and that there was no evidence of glyphosate causing chromosomal damage to DNA. For these reasons, NTP did not consider conducting a 2-year rodent cancer bioassay of glyphosate.

Oxidative Stress Studies

Exposures to glyphosate alone did not cause pronounced oxidative stress responses when compared to well-established positive and negative controls. In contrast, several GBF product mixtures produced some biomarkers of oxidative stress that did not correlate with the mixtures’ respective glyphosate content. These kinds of oxidative stress biomarkers are often associated with increased risk for cancer.

Across multiple experiments, glyphosate alone showed only weak biological activity, and only at concentrations much higher than typical real-world exposures. This was consistent with the lack of correlation between glyphosate content in the 13 GBF products evaluated and their respective biological activities. Collectively, these findings indicate non-glyphosate components of GBFs are likely driving biological responses observed in this study. Herbicide product labels list active ingredients, such as glyphosate, but other components are often considered "inert" for regulatory purposes and are not reported due to confidential business information protection for companies that manufacture herbicides.

Overall, the findings from our oxidative stress experiments indicate that it is unlikely that glyphosate could cause cancer through an oxidative stress mechanism. Our findings do not rule out the possibility that exposure to glyphosate might cause cancer through other mechanisms.

The new findings are consistent with the 1992 NTP studies referenced in the section above, in which rodents exposed to high levels of glyphosate in feed showed little evidence of toxicity.

See the table below for the most up-to-date information on the variety of projects taking place at NTP.

Study Description Status Findings  & Supporting Files

Oxidative Stress Testing

 Human cell-based tests to study DNA damage, oxidative stress, and cell viability Completed Supporting files
Genetic Toxicity Testing Human cell-based studies to determine the potential of glyphosate to cause DNA damage (genotoxicity) Completed Supporting files
Back to Top

Research at Other Agencies

United States
International
Back to Top

Informational Resources

The informational resources below provide additional details on NTP's research on glyphosate and glyphosate formulations.

FAQs

Q: Why does NTP care about studying glyphosate?
A: In 1992, NTP reported that rodents exposed to glyphosate in feed showed little evidence of toxicity, and there was no evidence of glyphosate causing damage to DNA. Since then, several public health agencies have reviewed the scientific literature to learn whether exposure to glyphosate is a cancer hazard for humans.

Due to different interpretations of the potential health risks of glyphosate exposure, major public concern about exposure risks, and reported differences in the toxicity of different glyphosate products, NTP has completed additional research on glyphosate and glyphosate-based formulations (GBFs), including testing the potential genetic and mechanistic toxicity.

Q: What is the impact of these NTP studies?
A: The approach methods used in these studies provide both the public and herbicide product manufacturers with a data-driven framework to identify safer product formulations with lower potential to cause oxidative stress and cancer in humans.

Q: Where can I find the data?
A: NTP has made the data from its genetic toxicity tests and high-throughput screening studies available in the Chemical Effects and Biological Systems database.

Q: What other chemicals related to glyphosate is the NTP testing?
A: NTP is testing glyphosate and several GBFs used for either agricultural or residential purposes. GBFs were selected to span a range of glyphosate concentrations. NTP is also testing (aminomethyl)phosphonic acid (AMPA), a metabolite of glyphosate that is produced by microbes, including the mammalian microbiome.

Substances were tested in the following cell-based genotoxicity assays, in the presence or absence of an exogenous rat liver metabolic activation system:

  • Bacterial mutagenicity assays with S. typhimurium tester strains TA100, TA98, TA97a, and TA1535, and E. coli tester strain WP2, to assess gene mutations
  • Micronucleus assay (human TK6 cells) to assess chromosomal damage
  • MultiFlow DNA Damage Assay (human TK6 cells) to identify the mechanism of action for induction of chromosomal damage (chromosome breaks versus chromosome loss)

Substances were tested in human liver or human skin cells using these assays:

  • CellTiter-Glo 2.0 Assay for cell death
  • ROS-Glo Assay for oxidative stress in cells
  • MitoSOX Red assay for oxidative stress inside of mitochondria
  • Phosphorylation of a chromatin protein called H2AX, an indicator of broken DNA
Presentations
Supporting Documents
Back to Top

Stay Informed & Contact Us

Laptop on wooden desk with email screen

Stay Informed

Subscribe to receive email to stay informed about glyphosate research and other NTP information.

Contact Us

For questions or additional information, email us or use our contact form.

Back to Top