Serious Reactions to Weight-Loss Jab Mounjaro Soar by Over 300% in a Single Year
The number of serious adverse reactions reported in connection with the weight-loss drug Mounjaro has surged by more than 300% in just one year in the UK, with total adverse reaction reports now exceeding 40,000, prompting growing calls for increased scrutiny of the medication's safety profile.
The sharp rise in reported reactions comes as Mounjaro — the brand name for tirzepatide — has become one of the most widely prescribed weight-loss medications in the UK, available on the NHS for adults with obesity and type 2 diabetes. The drug works by mimicking hormones that regulate appetite and blood sugar, and has been hailed as a breakthrough treatment for obesity.
Scale of the Problem
The most commonly reported adverse reactions involve the gastrointestinal system, including nausea, vomiting, diarrhoea, and constipation — side effects that are well-documented and typically most pronounced when patients first begin treatment or increase their dose. However, more serious reactions, including acute pancreatitis, severe allergic reactions, and significant dehydration leading to kidney complications, have also been reported with increasing frequency.
The dramatic increase in adverse reaction reports is partly attributable to the rapid growth in the number of patients taking the drug. However, health experts have warned that the rate of serious reactions per patient also appears to be rising, and that the full long-term safety profile of the medication remains incompletely understood.
NHS Prescription Charges Frozen
In a separate development, the UK government has confirmed that NHS prescription charges will remain frozen at £9.90 for the 2026-2027 period — a decision projected to save patients in England an estimated £12 million over the coming year. The freeze will be welcomed by the millions of patients who rely on regular prescriptions, including those taking weight-loss medications.
Why It Matters
The surge in Mounjaro reactions raises important questions about the pace at which new weight-loss drugs are being rolled out across the NHS and the adequacy of patient monitoring and follow-up. Healthcare professionals have emphasised the importance of patients reporting any side effects through the Yellow Card scheme operated by the Medicines and Healthcare products Regulatory Agency (MHRA).
Meanwhile, Irish pharmaceutical giant Novo Nordisk has announced a €432 million investment in its Irish operations for the production of the Wegovy weight-loss pill, underscoring the enormous commercial stakes in the obesity treatment market.
What's Next
The MHRA is expected to review the accumulating adverse reaction data and may issue updated guidance to prescribers. Patients currently taking Mounjaro are advised to consult their GP or pharmacist if they experience any concerning symptoms, and to report side effects through the Yellow Card scheme.
Read more at The Irish Sun.
