Mounjaro maintains weight loss over three years, study confirms
A new long-term study has confirmed that once-weekly doses of tirzepatide (branded as Mounjaro) can deliver significant and sustained weight loss for up to three years in adults living with overweight or obesity who do not have diabetes.
The findings were presented at the European Congress on Obesity (ECO) in Malaga, Spain, and build on earlier results from the SURMOUNT-1 trial. Researchers from the University of Padova in Italy, in collaboration with pharmaceutical manufacturer Eli Lilly and Company, found that weight loss patterns vary among individuals and may be influenced by factors such as sex and the presence of obesity-related health conditions.
An earlier phase of the SURMOUNT-1 trial in 2022 showed average weight losses between 15 per cent and 21 per cent after 72 weeks, depending on dosage. This updated analysis focused on 700 participants (predominantly women, average age 48) who adhered to their medication regime for three years.
All participants were either living with obesity (BMI over 30) or overweight (BMI over 27) with prediabetes. The study assessed how much weight participants lost over time and when they reached a weight loss plateau — defined as less than 5 per cent change in weight across a three-month period.
Researchers categorised participants into three groups based on weight loss trajectory:
Group 1 experienced steady weight loss of around 10 per cent and plateaued early.
Group 2 saw an initial drop of approximately 20 per cent before reaching a plateau later.
Group 3 achieved the most substantial weight loss — around 31 per cent — and took longest to plateau. This group included more women and individuals without obesity-related conditions.
Despite these differences, most participants maintained clinically meaningful weight loss over three years. Even modest weight reduction (around 5 per cent) is known to lower the risk of developing type 2 diabetes and improve cardiovascular health, while greater weight loss yields more substantial benefits.
Weight loss plateaus were common across all groups, usually occurring within the first 24 to 48 weeks of treatment. Researchers noted that plateaus are a natural biological response, as the body activates mechanisms to stabilise weight through complex hormonal interactions.
Importantly, the study did not reveal any new safety concerns. The most frequently reported side effects were nausea, diarrhoea and constipation.
Medical experts unaffiliated with the study welcomed the findings. Dr Mir Ali, a bariatric surgeon in California, described the results as encouraging, noting that weight loss plateaus are also observed in surgical patients. However, he stressed the need for clear patient guidance on expectations.
Dietitian Jordan Hill said the research supports long-term use of medical therapy for weight loss in people with prediabetes, adding that further research is needed to understand individual differences in response.