New research indicates that a significant majority of individuals who discontinue weight loss medications, such as Mounjaro, experience substantial weight regain. An international 36-week trial revealed that 82 percent of participants who had achieved meaningful weight loss while taking tirzepatide, the active ingredient in Mounjaro, regained at least 25 percent of that weight within a year of stopping the medication.

The clinical trial, involving 308 participants, was overseen by researchers from the University of Texas and funded by Eli Lilly, the drug's manufacturer. Participants initially took tirzepatide for 36 weeks and were then switched to a placebo drug for a year to monitor weight changes. During both phases, they were also prescribed a reduced calorie diet and encouraged to increase physical exercise. While the study, published in JAMA Internal Medicine, noted initial weight loss and health improvements while on the drug, the subsequent placebo period highlighted the challenge of maintaining results without continued pharmacological intervention.

The implications of weight regain extended beyond just pounds. Researchers observed a decrease in associated health improvements, including adverse changes in cholesterol levels and fasting insulin. Furthermore, those who regained weight also experienced an increase in blood pressure, elevating their risk of stroke. The study's authors concluded that, consistent with findings from similar obesity management medications, the withdrawal of tirzepatide led to weight regain despite ongoing lifestyle interventions, underscoring the critical importance of continuous obesity treatment.

Mounjaro, along with other popular weight loss injections like Ozempic and Wegovy, are classified as GLP-1 agonists. These drugs mimic naturally occurring hormones in the body, signalling it to produce more insulin when needed, reducing glucose production by the liver, and slowing digestion. Dubbed the 'King Kong' of weight loss drugs, Mounjaro has demonstrated potent effects, helping patients shed up to a fifth of their body weight in a year.

In the UK, Mounjaro is set to be offered to approximately 220,000 people over the next three years under new NHS prescribing rules. Previously available privately or at a limited number of specialist NHS weight loss clinics, GPs can now prescribe the drug to patients with a Body Mass Index (BMI) over 40 (classed as severely obese) who also have at least four obesity-related health conditions, such as type 2 diabetes, high blood pressure, or sleep apnoea.

The introduction of such medications comes amidst a long-standing obesity crisis in Britain, where two in three citizens are classified as overweight or obese. Weight-related illnesses contribute significantly to the economy's burden, estimated at £74 billion annually, with obesity costing the economy an estimated £100 billion per year. Overweight individuals face increased risks of serious health conditions including heart disease, cancer, and type 2 diabetes. Globally, more than 30 new GLP-1 drugs, including an oral pill from Novo Nordisk (maker of Wegovy and Ozempic), are currently in development, indicating a growing focus on pharmacological solutions for obesity management.