Spring has sprung and garden centres and DIY stores around the country are packed with customers seeking new plants – and something to tackle the weeds.
For this, many will turn to Roundup, the world’s most widely used weedkiller.
The choice of home gardeners, farmers and many local councils alike, Roundup contains glyphosate, which is absorbed through a plant’s leaves and travels down to the roots, where it blocks an enzyme the plant needs to make proteins – so starving it to death.
That makes it brutally effective on deep-rooted weeds such as bindweed and dock, which is why gardeners have relied on it for half a century.
But increasingly research is linking it to adverse effects, for instance, cancers such as non-Hodgkin lymphoma (a cancer of the lymph system).
And now a new study suggests the chemical may also be linked to mental health problems such as chronic anxiety and even dementia.
This could be down to its effect on the gut microbiome, say researchers at the University of Puerto Rico, writing in the journal Frontiers in Toxicology.
They have warned it kills off Lactobacillus, an important strain of bacteria in the gut that helps the body produce serotonin, a chemical messenger vital for mood control.
Organic wine maker Nick Dugmore, 41, says that glyphosate caused his bowel and lung cancer
Meanwhile, a major study that’s repeatedly been cited by Roundup’s maker, Monsanto, to prove its safety has recently been retracted by the science journal that published it.
This extraordinary development came after an investigation by a Harvard University researcher, which exposed that the ‘independent’ study had actually been ghostwritten – crafted with the help of Monsanto employees, but published under an expert’s name.
Against this background, the UK government is set to decide later this year whether to renew the safety licence for glyphosate – and will be asking the public for their view.
With evidence that glyphosate residues end up in food, campaigners hope that its use will at least be restricted for UK farming crops.
So how safe is glyphosate – either in your garden, or on the fields where our food is grown?
For the past decade glyphosate has been dogged by its potential link to cancer.
In 2015 the World Health Organisation concluded that from a review of published scientific evidence, glyphosate is ‘probably carcinogenic to humans’ – possibly through exposure from the air, or on the skin, or via food.
Then in 2018 a jury in California awarded £226million in damages to school groundsman Dewayne Johnson, who claimed that Roundup products had caused his non-Hodgkin lymphoma.
The jury found that Monsanto knew that Roundup weedkiller is dangerous and had failed to warn consumers.
More recently, in March this year researchers at Nebraska University – who reviewed a number of studies on glyphosate over the previous five years – concluded data provided ‘consistent, coherent and compelling evidence’ that glyphosate herbicides are a cause of non-Hodgkin lymphoma in humans exposed to them, reported the journal Clinical Lymphoma, Myeloma & Leukemia.
The manufacturer has always disputed the link.
It has, however, agreed settlements in nearly 100,000 other Roundup cancer claims, paying approximately £8billion, according to the US Lawsuit Information Centre.
Last year Bayer, which acquired Monsanto in 2018, announced that around 61,000 active Roundup lawsuits were pending in the US.
It now says ‘those numbers are no longer accurate – in part because we reached some confidential settlements’. But it stresses that the settlements it has agreed ‘do not contain any admission of liability or wrongdoing’.
A mainstay of the manufacturer’s defence has been a landmark study on the herbicide’s claimed safety, published 25 years ago in the journal Regulatory Toxicology and Pharmacology.
The study influenced regulators’ decisions on glyphosate and Roundup for decades.
For example, it was cited some 40 times in the 2015 expert report which led to the Roundup being re-authorised as safe to use in the European Union in 2017.
What’s more, the study ranked in the top 0.1 per cent of most-cited scientific studies about glyphosate, according to Naomi Oreskes, a professor of the history of science at Harvard University, and Alexander Kaurov, an independent researcher.
In September last year these two researchers exposed the study as having been ghostwritten, with Monsanto employees helping craft the paper – they declared in the journal Environmental Science & Policy that ‘corporate ghostwriting is a form of scientific fraud’.
NIck camped out after working on an adjacent farm and walked the fields barefoot. He later discovered that the other farmer had sprayed his land with glyphosate
Glyphosate is absorbed through a plant’s leaves and travels down to the roots, where it blocks an enzyme the plant needs to make proteins – so starving it to death
In response, the editor-in-chief of the journal Regulatory Toxicology and Pharmacology retracted the long-standing glyphosate study, explaining that ‘the apparent contributions of Monsanto employees as co-writers to this article were not explicitly mentioned as such in the acknowledgments section’.
Bayer maintains that Monsanto’s role was adequately disclosed.
Aside from being exposed to the weedkiller when spraying it on our plants, we mostly are contaminated with glyphosate through our daily diets.
And the foods highest in glyphosate residues are generally conventionally grown (i.e. non organic) cereals, such as wheat, oats and barley; pulses such as peas; and other crops including sugar beet, potatoes, flax, oilseed rape and sunflowers that are sprayed with the weedkiller just before harvest, according to the UK campaign group, the Pesticide Action Network UK (PAN UK).
In the EU pre-harvest spraying has been banned since 2023.
Farmers in this country are allowed to use this technique – known as pre-harvest desiccation – to douse crops in glyphosate to kill them, making the grain ripen faster and dry more uniformly (so they don’t rot in storage).
PAN UK claims common products which contain significantly high levels of glyphosate include breakfast cereals, granola bars, beer and wine (though organic products may be free from it).
While UK exposure levels have yet to be studied, US research suggests that many people’s bodies are polluted with glyphosate.
A study in 2022 conducted by the government body, the US Centers for Disease Control and Prevention – and published in the journal Environment International – concluded that: ‘An estimated 81 per cent of the US population has had recent exposure to glyphosate, either through diet, skin contact and breathing in particles from the air.’
And possible harms continue to emerge.
Organic wine maker Nick Dugmore, 41, is convinced that glyphosate caused his bowel and lung cancer.
Four years ago he was helping out on an adjacent farm, where he camped out and walked around the fields in bare feet, pruning, when he developed an angry itchy rash all over his body and his face swelled.
The rash lasted for six weeks – and Nick later discovered that the other farmer had sprayed his land with glyphosate: he himself ‘never uses it on my own crops, because I do not believe in using herbicides’.
Just over a year later Nick was diagnosed with stage 3 bowel cancer (meaning it had spread to nearby lymph nodes).
‘My consultant said it was around 14 months’ old in terms of size,’ says Nick.
‘While I underwent chemo and radiotherapy, I cast my mind back exactly 14 months – it was the time I had been exposed to glyphosate.’
As the father of two explains, he’d always been fit and healthy – he and his wife Rebecca, 40, and their two children, Finlay, 7, and Flora, 5 ate organic food and he’d farmed only organically for years.
‘I’m convinced glyphosate was the cause of my cancer – I’ve since discovered there is a link between it and disruption of the gut lining.’
Chemotherapy and radiotherapy eradicated his bowel cancer, but Nick, who lives in Willunga in South Australia, has recently discovered he has two tumours on his lungs; his cancer is now stage 4.
While there is some evidence that herbicides such as glyphosate may cause some blood cancers, it’s yet to be shown that it is linked with bowel cancer.
But the latest study suggests a new link – to mental illness.
In the study at the University of Puerto Rico, lab rats drinking glyphosate daily for 16 weeks (in doses to what we might get from dietary exposure) developed fearful hypervigilance toward harmless objects and sounds.
The amounts of glyphosate the rats drank is equivalent to those legally approved as ‘safe’ for human dietary consumption.
The study showed that the rats’ anxious behaviour was accompanied by abnormal changes in a region of the brain called the bed nucleus of the stria terminalis, which is heavily involved in identifying threats and can drive anxiety in humans.
The researchers believe that glyphosate can disrupt the healthy balance of bacteria in the digestive tract, thought to play a key role in mental health.
They said that the glyphosate-exposed rats’ guts showed that a significant drop in a bacterial group, Lactobacillus. This is essential for processing dietary proteins into the chemical messenger, serotonin.
The study reinforces earlier research in 2023 by biologists at Leipzig University, which found that when pregnant rats consume glyphosate in their diets, their offspring grow to have both altered gut microbiomes and raised levels of anxiety and social phobia.
The researchers here said the most likely explanation was that the babies consumed glyphosate via their mothers’ milk.
In 2018 a jury in California awarded £226million in damages to school groundsman Dewayne Johnson, who claimed that Roundup products had caused his non-Hodgkin lymphoma
As well as potentially disrupting our brains through our microbiomes, glyphosate may also directly cause harm to the brain, according to researchers at Arizona State University.
Last year they warned that the chemical can enter the bloodstream, cross the blood-brain barrier – the physical barrier that protects the brain against toxins – and cause inflammation, which in turn may cause the type of damage to brain cells seen in Alzheimer’s disease.
Their lab-based study, published in the Journal of Neuroinflammation, warns that chemical components of glyphosate stay in the brain long after exposure ends.
For the study, cells from brain tissue samples that were exposed to glyphosate died prematurely or developed abnormalities associated with dementia.
The damage continued to occur even after the samples were no longer being exposed to glyphosate, because the tissues had built up accumulations of a toxic by-product of glyphosate, called aminomethylphosphonic acid, the researchers explained.
Neurological damage from glyphosate is already being seen in children and older people, according to other recent studies.
For example, in the journal Environmental Research in 2024 researchers from four US universities found that children whose mothers had been exposed by farming to glyphosate while pregnant were significantly more likely to show delayed development in walking and talking at the age of two.
Meanwhile, urine samples from people aged over 70 who had dementia symptoms showed exposure to glyphosate, according to a study in the Journal of Alzheimer’s Disease in 2024.
The researchers concluded that the weedkiller was ‘significantly linked to increased cognitive function impairment’.
Michael Antoniou, a professor emeritus of molecular genetics and toxicology at King’s College London, told Good Health he was not surprised by the latest findings.
He said that consuming glyphosate in our diets ‘could be a contributory factor to mental health problems’.
In 2021, he led a lab-based study, published in the journal Environmental Health Perspectives which found that exposure to glyphosate – and its commercial Roundup formulation – can disrupt the function of the gut microbiome and body systems, with potentially serious effects.
‘Glyphosate could harm mental health directly by crossing the blood-brain barrier and interfering with normal brain cell communication by interfering with our neurotransmitters [chemical messengers], or indirectly by disrupting our gut microbiomes,’ he says.
‘More research is needed to confirm this possibility.’
He adds: ‘What we do know for certain is that glyphosate at UK-approved doses causes numerous types of cancer in rats.’
Other research has suggested potential links to liver disease and birth defects.
‘The UK’s approved level needs to be drastically reduced – by at least 100-fold in my view – as a matter of urgency to better protect public health,’ says Professor Antoniou.
‘This needs to go hand-in-hand with measures to reduce public exposure.’
Yet the UK use of glyphosate on crops has increased massively over recent years – according to a study of official government data published last month by PAN UK, rising by 1,000 per cent over 35 years, from 200 metric tonnes per year in 1990 to more than 2,200 tonnes in 2024.
During the same time period, it says, the area of UK farmland treated with the toxic herbicide increased tenfold to over 2.6 million hectares in 2024.
Nick Mole, policy manager at PAN UK, says: ‘These figures reveal that the UK’s glyphosate addiction has spiralled out of control and we continue to spray it on the food we eat.
‘The government urgently needs to commit to phase out glyphosate and ultimately ban it.’
While PAN UK is calling for glyphosate not to be reapproved at all – along with other groups, such as the Soil Association, it believes that at the very least that pre-harvest desiccation should be prohibited as it is in the EU.
Some European countries have already gone further than this.
In 2021 the Austrian parliament voted to ban the use of glyphosate for private use and in sensitive areas such as playgrounds and parks.
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In a similar vein, Germany prohibits glyphosate use in public spaces, and France heavily restricts its use on arable crops and vineyards.
This year the UK government will make a crucial decision whether to renew the herbicide’s safety licence, which could allow its continued use here for the next 15 years.
UK farming organisations are lobbying for continued permission to use glyphosate, including as a pre-harvest desiccant, claiming it is vital to protect crops and keep farms in business.
They are supported by the Glyphosate Renewal Group, a coalition of chemical companies that includes Roundup’s manufacturer, Bayer.
A spokeswoman for the Health & Safety Executive (HSE) told Good Health: ‘HSE is still working on the renewal assessment. This will include a 60-day public consultation expected to take place this summer.’
Professor Antoniou, who believes that pre-harvest desiccation should be banned, says that maximum safe human-consumption levels should be significantly reduced.
He adds: ‘If the HSE truly and fully took on board the latest science showing definitively that glyphosate exposure is a cancer hazard, then it would recommend a ban.
‘But I’m not holding my breath on this. Glyphosate is embedded in economics, farmer convenience and politics – which muddies the whole issue.’
Nick, meanwhile, ‘wants to warn people of the dangers of this “safe” weedkiller’.
Bayer told Good Health: ‘Glyphosate-based herbicides are some of the most thoroughly studied products of their kind.
‘For decades, there is overwhelming consensus among the leading health authorities around the world that glyphosate can be used safely.’
As for the journal article retraction, Bayer says the paper is now outdated and not used in recent EU decisions to re-approve glyphosate.
Case study interview: Julie Cook
