UK Regulator Reports 150,000 Adverse Events and 153 Deaths Linked to Weight-Loss Jabs

Weight-loss medication patients in the UK have filed about 150,000 reports of adverse side-effects, and more than 150 deaths have been linked to the drugs, according to figures published by the Medicines and Healthcare Products Regulatory Agency (MHRA). Separately, a study in JAMA Network Open found that overweight adults who switched to a low-fat plant-based diet lost an average of 5.9kg in four months, compared with around 6.9kg over nine months in trials of semaglutide, the active ingredient in Ozempic and Wegovy.

The figures, collected through the MHRA's Yellow Card scheme, show thousands of reports have been made about all of the GLP-1 weight-loss drugs available through the NHS, including liraglutide, also known as Saxenda; semaglutide, offered as Wegovy; and tirzepatide, also known as Mounjaro. There were more than 100,000 reports of adverse effects from tirzepatide – some 10,000 of them classed as “serious” – and the MHRA has potentially linked 98 deaths to the medication. For Wegovy, 44,000 adverse reactions were reported, 4,800 of those categorised as serious, and 37 resulted in death. For liraglutide, some 3,000 reports were made of adverse reactions, 734 defined as “serious”, and 18 resulted in a “fatal outcome”. It is thought about 1.6 million people are on weight-loss drugs in the UK.

The Yellow Card scheme allows more than one report per patient, meaning the figure does not reflect the total number of individuals complaining of side-effects. Fatal outcomes could be caused by underlying or undiagnosed illnesses, unrelated to the treatments. In January this year, the MHRA updated its product information to strengthen its guidance regarding severe pancreatitis, including warnings of necrotising and fatal pancreatitis, following an increase in reports to the Yellow Card scheme of severe and acute pancreatitis.

A coroner in Norfolk was examining whether the death of a 73-year-old woman could be linked to weight-loss jabs after she died in 2024 following an increase in her dose of Mounjaro. A coroner for Devon and Plymouth opened an inquest into the death of a 66-year-old woman, claiming a GLP-1 agonist weight-loss medication had contributed to her death on July 23. The reports come after a host of lawsuits were filed in the US against both jab manufacturers, Novo Nordisk and Eli Lilly. Eli Lilly, the maker of Mounjaro, said sales of the drug had doubled this year globally.

A Novo Nordisk spokesperson said: “We care deeply about patient safety. Like all medicines, treatments used for chronic conditions can have side-effects, and these can vary from person to person. That is why medicines should be prescribed by, and used under the supervision of, a healthcare professional, who can consider the potential benefits and risks for each individual.” An Eli Lilly spokesperson said: “We take reports regarding patient safety seriously and actively monitor, evaluate and report safety information for all our medicines.”

In the separate study, published in JAMA Network Open, researchers followed 224 overweight adults, most of them women with an average age of 54, who were split into two groups. One group adopted a vegan diet packed with fruit, vegetables, grains and legumes such as beans and chickpeas, while avoiding meat, fish, dairy products and eggs; the other group continued eating their usual diet. After 16 weeks, those following the plant-based plan had increased their vegetable intake by around 150g a day and their fruit intake by about 80g, almost tripled their consumption of legumes, and more than doubled their intake of plant-based meat alternatives. The vegan group reduced their daily calorie intake by almost 500 calories, dropping from an average of 1,834 calories a day to 1,343.

The scientists said the diet “may be an effective treatment for overweight adults”. They explained that plant-based foods contain more water and fibre while being lower in fat, allowing people to eat a similar amount of food while consuming fewer calories. The study also found the vegan diet improved blood sugar control, reduced fat stored in the liver and muscles, and increased the number of calories burned during digestion. However, the researchers warned that the findings have limitations because participants reported their own diets and volunteered for the study.

Around 3.5 million people in the UK are estimated to follow a plant-based diet, which has previously been linked with lower risks of heart disease, diabetes and some cancers. But experts have warned vegans need to plan their diets carefully to avoid deficiencies, particularly vitamin B12. The National Health Service (NHS) recommends vegans take a daily B12 supplement because the nutrient is mainly found in animal products such as meat, fish, milk and eggs. A consultant trauma and orthopaedic surgeon at Addenbrooke's Hospital in Cambridge warned: “This is a vitamin that is fundamental to the function of the human body, and it is almost entirely absent from a vegan diet. If supplements are not taken, after six months of going vegan, people can start to experience neurological symptoms such as anxiety, depression and even psychosis.”