Significant Rise in Adverse Reactions from Mounjaro Reported

Last year, there was a staggering 300 percent spike in adverse reactions associated with Mounjaro, with health authorities documenting 71 fatalities.

Information gathered by the Medicines and Healthcare products Regulatory Agency (MHRA) through its Yellow Card Scheme, which enables patients to report any suspected side effects or adverse drug events, indicates that there were 40,245 reported reactions to Mounjaro in the UK in 2025.

Among these, 6,755 reactions were deemed ‘serious,’ leading to 71 deaths. This marks an almost 340 percent increase from 2024, which recorded 9,153 reactions, of which only 13 were fatal.

The predominant side effect observed in 2025 was gastrointestinal disorders, with 37,546 cases reported, including 19 fatalities.

The NHS outlines side effects like nausea, diarrhea, and abdominal cramps, and many individuals have shared their troubling experiences with these symptoms while undergoing the weekly injections.

For instance, 60-year-old Karen Coe described her side effects as excruciating, likening her experience to feeling as if she were being ‘ripped open by a knife.’

Ms. Coe began her weight-loss injections to address type 2 diabetes, receiving her first dose on March 14, 2025.

Following her initial jab, she experienced dizziness and a headache. Three days later, she suffered intense stomach pain and severe diarrhea, prompting her to call an ambulance.

She recounted, “I nearly passed out. I was dizzy and felt really cold.”

However, upon examination at the hospital, no serious issues were identified.

After just one injection, she spent the following day grappling with stomach cramps and blood in her stool. Her symptoms initially subsided, but on March 24, she noticed ‘massive blood clots,’ which led to a rush to A&E.

Medical evaluations resulted in a referral to a colorectal surgeon, with doctors suggesting her initial symptoms were likely due to Mounjaro, although they did not confirm the reason for her later clotting complications.

She was advised to monitor her conditions, leading to a period of weakness and difficulty eating.

Ms. Coe noted, “Every few minutes, I’d go to the bathroom and see blood.”

Deciding against continuing her Mounjaro treatment, she warned others, “It can cause severe reactions and side effects. People should really think carefully and not take it lightly.”

It’s interesting to note that women accounted for the majority of side effect reports, totaling 32,075 last year.

The age group with the most reports was 30-39 years, which had 1,397 submissions.

In contrast, reactions to other weight-loss injections, like Semaglutide (also known as Ozempic), showed a downward trend, suggesting a shift in user preferences.

Reports for Ozempic in 2024 totaled 8,938, with nine fatalities. The following year, there was a slight drop to 7,146 reports but a rise in fatal outcomes to 19.

The Yellow Card site emphasizes that reported information shouldn’t be seen as a comprehensive list of potential side effects or used to compare the safety of different medications.

Eli Lilly and Company, Mounjaro’s sole manufacturer, stated their commitment to patient safety, acknowledging the importance of monitoring and evaluating safety data for all medicines.

They encouraged patients to discuss any side effects with their healthcare providers to ensure they receive genuine Lilly products.

Recently, the MHRA updated the product information for Mounjaro, Ozempic, and Wegovy to include the potential for a ‘small risk of severe acute pancreatitis,’ which is an intense inflammation of the pancreas that can develop quickly.

Typical symptoms involve intense abdominal and back pain that doesn’t subside, along with fever and vomiting. While many patients feel better within a week, complications can arise, including tissue death in the pancreas, which poses risks of infection, sepsis, and organ failure.

A notable case involved Susan McGowan, who passed away from multiple organ failure linked to pancreatitis after receiving two low-dose injections of tirzepatide. Her death certificate noted acute pancreatitis as a key cause, with her use of Mounjaro marked as a contributing factor.

This incident was the first death officially tied to the medication in the UK. At that time, Dr. Alison Cave of the MHRA conveyed sympathy to the family while asserting that current evidence suggested the benefits of these medications outweighed potential risks when used appropriately.

Currently, it is estimated that around 1.6 million individuals in England, Wales, and Scotland have utilized weight-loss injections over the past year.