Adults newly diagnosed with severe mental illness (SMI) gain almost four kilograms more than their peers within 15 years but are no more likely to be referred to structured weight-management programmes, according to new research published in The Lancet Psychiatry.
The University of Oxford led research, supported by the National Institute for Health and Care Research (NIHR), tracked 113,904 adults (including 23,025 with SMI matched to 90,879 without) across 1,454 GP practices. People with SMI gained 5.6 kilograms compared to 1.6kg in those without by year 15 – a difference of 4kg.
Twelve people with lived experience of SMI co-designed the study and advised on outcome selection, ensuring the research addressed real-world concerns about both physical health outcomes and service access.
Most concerning was the rapid weight gain in the crucial first five years after diagnosis, when people with SMI gained 4.9kg compared to 1.6kg in people without SMI – a difference of more than 3kg. This weight gain was most pronounced in younger adults aged 40 and under, and those taking antipsychotic medications.
After accounting for factors including age, sex, race and ethnicity, socioeconomic status, alcohol consumption, smoking status, and BMI, people with SMI and a BMI of 25 kg/m² or higher were 10% more likely than people without SMI to receive weight management advice from GPs (incidence rate ratio 1.10, 95% CI 1.07–1.13). However, they were no more likely to be referred to structured weight management programmes (incidence rate ratio 1.00, 95% CI 0.91–1.10), highlighting a significant gap between problem recognition and service provision.
"Weight gain in people with severe mental illness isn't just a number on a scale. It has real consequences for their heart health and life expectancy," said Dr Charlotte Lee, lead author and Senior Research Associate in Qualitative Research at the Centre for Academic Primary Care, University of Bristol and Research Fellow at the University of Oxford's Nuffield Department of Primary Care Health Sciences, where the research was undertaken.
"Our findings identify a clear window of opportunity. Embedding weight-management referrals into early psychosis care pathways could reverse years of preventable cardiovascular harm."
The findings directly support priorities in the NHS 10 Year Health Plan, particularly its focus on prevention, shifting care from hospital to community through the Neighbourhood Health Service, and addressing health inequalities.
People with SMI die on average 15 years earlier than the general population, largely due to preventable cardiovascular disease. Excess weight is a key driver of this health inequality, often worsened by antipsychotic medications essential for managing symptoms.
The research revealed that approximately 80% of people with SMI had been prescribed antipsychotics, with longer duration of use associated with greater weight gains. However, even those not prescribed antipsychotics still gained more weight than people without SMI, suggesting the conditions themselves may contribute to weight gain.
"When I was first diagnosed, nobody warned me about the weight gain or offered help to prevent it. My weight ballooned and I gained two stone in the first year alone", said Alex, a member of the study's lived experience advisory panel.
“This research validates what many of us have experienced – we're told to watch our weight but not given the same access to support as everyone else. We need a more holistic approach tailored to our mental health condition as well as our diet, physical activity and other lifestyle factors. Staff with the right training and skills at Early intervention stage, could have changed my whole health journey. I wish that the support had been there from the start.”
The study, which followed people for up to 15 years using primary care (GP) records, represents the most comprehensive analysis to date of long-term weight trajectories in people with conditions including schizophrenia, bipolar disorder, and other psychotic disorders. As with all routine healthcare data studies, findings should be interpreted with awareness of potential limitations such as recording delays or measurement frequency variations.
The research highlights the need for proactive weight management support in the early stages following diagnosis to help prevent obesity, type 2 diabetes, and cardiovascular disease in this vulnerable population, aligning with the 10 Year Health Plan's prevention agenda and its commitment to tackling the "obesity epidemic" through both lifestyle interventions and new treatments.
This is based on a story originally posted on the Nuffield Department of Primary Care Health Sciences
Paper: Weight trajectories and access to weight management services in individuals with severe mental illness in the UK: a population-based, matched cohort study by Charlotte Lee et al. Published in The Lancet Psychiatry. September 2025.
Comment: Weight management in severe mental illness: bridging the gap between guidelines and primary care. Sri Mahavir Agarwal et al. The Lancet Psychiatry. September 2025.
Conversation article: Serious mental illness often brings rapid weight gain - but support is missing. Charlotte Lee. Published in The Conversation. September 2025.