New Zealand's approval of the weedkiller Roundup rests on industry-funded scientific reviews that are currently under investigation or have been retracted, according to a new analysis. This reliance on compromised evidence undermines the country's regulatory process for glyphosate, the active ingredient in Roundup.
Conflicting International Assessments
The US Environmental Protection Agency (EPA) has judged glyphosate “not likely” to cause cancer, while the World Health Organization’s International Agency for Research on Cancer (IARC) describes it as “probably carcinogenic to humans”. The two agencies weigh evidence differently: IARC uses only publicly available studies and tests animal data for dose-response trends, while the US EPA leans heavily on unpublished studies commissioned by the manufacturer, formerly Monsanto and now owned by Bayer.
New Zealand, lacking resources for full risk assessments of thousands of chemicals, relies on findings from larger overseas agencies. In the case of glyphosate, its approval process is based on several reviews shaped by Monsanto. One of these has been retracted, and two are under investigation, according to the analysis published in The Conversation.
Compromised Evidence in Regulatory Decisions
Monsanto-produced evidence has a questionable track record. Its early tests during the 1970s and ‘80s were conducted in contract laboratories that have since been convicted of fabricating data. In 2017, litigation forced Monsanto’s internal documents to be unsealed, exposing how the company interacted with researchers who gave favourable assessments and produced ghostwritten reviews. Ghostwriting, where independent scientists’ names are placed on work produced by company employees, is explicitly prohibited under scientific standards.
Faced with divided evidence, New Zealand’s Environmental Protection Authority (NZ EPA) commissioned its own report in 2016. It concluded glyphosate is “unlikely to be genotoxic or carcinogenic to humans”. New Zealand scientists objected at the time. In 2018, six public-health researchers, several connected to IARC, challenged the authority’s report, citing reliance on unpublished industry studies and ghostwriting. The authority maintained its position, and in 2024 again found no grounds to reassess glyphosate. A High Court challenge to this decision was unsuccessful.
Three Key Monsanto Reviews Under Scrutiny
Over the past year, researchers traced how Monsanto-influenced reviews shape global public discourse and regulation. They found these reviews effectively convinced people and regulators of glyphosate’s safety. One review, written by Monsanto and signed by outside academics, was retracted in November 2025 after an internal email described the practice of writing sections so named authors “would just edit & sign their names”. The journal noted Monsanto employees “may have contributed without proper acknowledgement as co-authors”.
Another review, also shaped by Monsanto, had a company scientist deliberately kept off the byline to make it look independent. A recently disclosed memo shows the US EPA’s own investigator concluded the paper “hid Monsanto’s role as an author”, but the agency kept citing it. A third review, published in 2015, discredited a study that found glyphosate caused a significant rise in malignant lymphoma in mice, invoking a “viral infection” instead. Subsequent independent reanalysis found no evidence of this in the original study.
Bayer continues to reject the ghostwriting characterisation, stating Monsanto’s involvement was appropriately cited in acknowledgments thanking the company’s scientists for “significant contributions”.
NZ Should Reconsider Glyphosate Regulation
Institutional trust varies significantly. US EPA emails from 2025 show Bayer promising the agency “a small thanks” for updating its glyphosate webpage. By contrast, the judge in Australia’s 2024 Roundup class action warned that a company dealing with regulators cannot be assumed to “play with a straight bat”, and the evidence gave him “concerns about accepting anything from Monsanto at face value”. Yet the 2015 review was used by the applicant’s own statistician.
New Zealand’s 2016 report also leans on these three reviews. Now, in 2026, it is much harder to treat them as legitimate evidence in an honest scientific debate about glyphosate’s safety. When New Zealanders are told dietary exposure sits well under 1% of the “acceptable level”, they should keep in mind two things: this level is based on industry-sponsored studies, and an average hides how unevenly exposure falls on sprayers, rural communities and people with particular diets. These factors should be weighted in, but New Zealand holds almost no exposure data.
Glyphosate is only one of 16 high-use pesticides in New Zealand flagged as suspected carcinogens by at least one major agency. The costs of using them should be estimated explicitly: an uptick in illnesses, strain on the healthcare system, harm to the environment and lost quality of life. The intellectually honest process would be to assess risks with broad scientific consultation and acknowledgement of where evidence is compromised or plainly missing. For New Zealand to keep avoiding a comprehensive reassessment of glyphosate is to make wilful ignorance a matter of national policy.
