A woman who lost more than six stone after being prescribed the weight-loss injection Mounjaro believed her prayers had been answered — until she was admitted to hospital in agonising pain. Her case has emerged as doctors warn of a devastating side effect that is becoming increasingly common among users of the drug, and identify which patients are most at risk.
Mounjaro, also known as tirzepatide, has become one of the most sought-after treatments for obesity and type 2 diabetes in the UK. It works by mimicking hormones that regulate appetite and blood sugar, helping patients to eat less and lose significant amounts of weight. For many, the results have been transformative. But the experience of patients such as Kat shows that the drug is not without serious consequences.
According to the accounts now being reported, Kat shed more than six stone while using the injection. The weight loss was exactly what she had hoped for, and she regarded the treatment as a breakthrough. The relief was short-lived. She later developed severe abdominal pain that became so intense she required hospital care. Doctors treating her linked the symptoms to a side effect of the medication that is being seen more frequently as prescriptions rise.
The side effect in question affects the digestive system and can cause debilitating pain, nausea and other complications. While many users experience only mild and temporary discomfort, a proportion develop reactions serious enough to require medical intervention. Clinicians say the risk is not evenly distributed across all patients, and they have begun to identify the groups most vulnerable to the complication.
Those most at risk are understood to include people with a history of gastrointestinal problems, those who escalate their dose too quickly, and patients who ignore early warning signs in the pursuit of faster weight loss. Doctors stress that the drug remains effective and appropriate for many people, but they caution that it must be used under proper medical supervision and that symptoms should never be dismissed.
The case has renewed debate about the rapid expansion of weight-loss injections, which have moved from specialist clinics into mainstream use in a matter of years. Demand has surged across Britain, driven by celebrity endorsements, social media discussion and the promise of rapid results. Regulators and health bodies have repeatedly urged patients to obtain the medication through legitimate prescribers rather than online sellers offering cut-price supplies.
For patients like Kat, the calculation has become more complicated. The drug delivered the weight loss she wanted, but at a cost she had not anticipated. Her story is being shared as a cautionary example at a time when millions are considering whether to start treatment.
Doctors say the key message is not that the injections should be avoided, but that patients must be fully informed about the risks and monitored closely. Anyone who develops severe or persistent abdominal pain while using the medication should seek medical help promptly. Early recognition of the side effect can make the difference between a manageable reaction and a hospital admission.
The growing number of such cases is likely to intensify scrutiny of how weight-loss drugs are prescribed, monitored and discussed in public. As demand continues to rise, the balance between benefit and harm will remain central to the conversation — and patients are being urged to weigh both sides before beginning treatment.