Weight loss jabs like Mounjaro linked to ‘silent cancer’ that is surging in under-50s, warn experts: ‘We need to find out more’
Weight-loss jabs may raise the risk of kidney cancer—a ‘silent killer’ now striking more under-50s—even as new research suggests they could protect against other tumours.
The alarm comes from the biggest study yet of patients on slimming injections such as Ozempic and Mounjaro, which tracked nearly 44,000 overweight and obese people for up to ten years.
While the drugs were linked to a 17 per cent lower risk of cancer overall—with big drops in ovarian and womb tumours—researchers also uncovered a disturbing signal for kidney cancer.
Patients on the jabs were about a third more likely to develop the disease than those who did not take them, with the risk highest among the under-65s and people who were overweight.
Kidney cancer is one of the fastest-rising cancers in Britain and the US and is often dubbed a ‘silent killer’ because it rarely causes symptoms until it is advanced.
Doctors warn that by the time tell-tale signs such as blood in the urine, persistent back pain or a lump under the ribs appear, it is often too late for successful treatment.
Almost 14,000 Britons are diagnosed every year, with 4,700 deaths. In the US, there are around 80,000 new cases annually.
If spotted early, three-quarters of patients survive at least five years – but once the cancer has spread, survival drops to just 18 per cent.
Mounjaro, Ozempic and other fat-melting injections have ushered in a new era in the war on obesity, but have also been linked to other health benefits, such as slashing the risk of heart attacks, strokes and kidney disease
Cases are also climbing sharply in younger adults.
People born in 1990 are up to three times more likely to develop the disease than those born in the 1950s—a trend doctors say is partly driven by rising obesity and high blood pressure.
The study, published in JAMA Oncology, compared 43,317 people prescribed the jabs with 43,315 who did not take them.
In total, 891 cancers were diagnosed among jab users compared with 1,022 in non-users.
But for kidney cancer there were 83 cases among users compared with 58 among non-users.
Dr Hao Dai, a health data scientist at Indiana University who led the research, also expressed concern about the uptick in kidney cancer among users.
‘We need to do another observational study to confirm that these drugs increase the risk,’ he said.
‘But from my point of view, it might be that the drugs raise the risk of some types of kidney cancer.
‘We don’t know, however, and need to do more research.’
One theory is that the drug’s common side effects, including severe nausea, vomiting, and dehydration, may trigger repeated bouts of acute kidney injury.
Over time, that stress could damage kidney tissue and increase the risk of mutations that lead to cancer.
Another area of concern is that the kidneys contain GLP-1 receptors. These are the same receptors Ozempic targets to regulate blood sugar and keep people full.
Some scientists wonder whether constantly stimulating these receptors could cause cells in the kidneys to grow out of control, though this remains speculative and has not been proven in humans.
Rapid weight loss and dramatic metabolic shifts caused by the drug might also play a role, potentially altering the body’s immune response or revealing preexisting kidney issues.
However Professor Paul Pharoah, a cancer specialist at Cedars-Sinai Medical Center in Los Angeles, urged caution over the findings.
He said: ‘While these results suggest that GLP1 receptor agonist have an effect on cancer risk the presence of an association does not mean that the association is a causal one.’
Dr Stephen Lawrence, associate clinical professor at the University of Warwick, added: ‘There was a slight uptick among users—two cases per 1,000 patients per year compared with 1.3 per 1,000 for non-users.
‘That’s about six extra cases for every 10,000 patients treated over a year. Not ideal, but still a drop in the ocean against other health benefits.’
He added: ‘Further research is needed before drawing any firm conclusions. The science is promising, but more research will be important to confirm these findings as more individuals begin these treatments.’
At the same time, scientists found people on the jabs were significantly less likely to be diagnosed with other cancers.
Rates of ovarian cancer fell by nearly half, while cases of womb cancer and certain brain tumours (meningiomas) also dropped.
Overall, patients on the injections had a 17 per cent lower chance of developing cancer of any type compared with those who did not take them.
The study was presented at the American Clinical Society of Oncology’s annual conference in Chicago, Illinois, the largest cancer conference in the world.
But experts remain cautious about over-interpreting the data, stating that the drop in cancer risk might simply be a result of weight loss itself, rather than the drugs.
Slimming jabs have already been credited with cutting the risk of heart attacks, strokes and kidney failure, on top of their dramatic weight-loss effects.
Experts say the latest results underline that while they may offer protection against some cancers, vigilance is still needed over the warning signs for kidney disease.
