Obesity as a Chronic Disease: Why Medication Has a Role

Obesity treatment in the UK is increasingly approached in the same way as other long-term conditions such as high blood pressure or type 2 diabetes. It combines diet, activity and behavioural support, and for some people adds medication or surgery, with ongoing review. The shift reflects evidence that the body actively defends its weight after weight loss, which is why many people regain weight despite their efforts. Licensed medicines such as Wegovy and Mounjaro now have a defined place in NICE guidance, but they are one tool among several, and whether they suit you is a decision for a prescriber.

What it means to call obesity a chronic disease

A chronic disease is a long-lasting condition that usually needs ongoing management rather than a one-off cure. The World Health Organization describes obesity as a chronic, complex disease, and organisations such as the Royal College of Physicians have argued for recognising it as such in the UK.

Calling obesity a disease is not about labelling individuals. It is about recognising three things:

1. It has biological causes. Genes, hormones, brain signalling and the gut all influence appetite and weight.
2. It tends to persist and relapse. Short-term efforts often produce short-term results.
3. It causes harm. Obesity raises the risk of type 2 diabetes, heart disease, stroke, some cancers, osteoarthritis, sleep apnoea, fatty liver disease and mental health problems.

The clinical obesity debate

Not everyone agrees on how to define obesity as a disease. BMI is a simple screening measure, but it does not distinguish fat from muscle or show where fat is stored, and it says nothing about whether someone is actually unwell.

In January 2025, the Lancet Diabetes & Endocrinology Commission on clinical obesity, led by a professor at King's College London, proposed a new framework:

The Commission also recommended confirming excess fat with other measures, such as waist circumference or waist-to-height ratio, rather than relying on BMI alone. This framework has been influential, but it has not replaced BMI-based criteria in UK licences or NICE guidance at the time of writing.

NICE guideline NG246 already encourages clinicians to use waist-to-height ratio alongside BMI, and to consider lower BMI thresholds for people from South Asian, Chinese, other Asian, Middle Eastern, Black African and African-Caribbean backgrounds, who tend to develop weight-related health problems at lower BMIs. Our guide to BMI thresholds and ethnicity explains why.

How common is obesity in the UK?

The Health Survey for England 2022 found that 64% of adults in England were living with overweight or obesity, including 29% living with obesity. The figures were similar to those reported in 2019, suggesting prevalence has remained broadly stable in recent years at a high level. Rates differ by age, sex, region and deprivation.

These numbers matter because they explain why the NHS cannot offer every possible treatment to everyone at once, and why NICE and NHS England have phased the introduction of newer medicines.

Why weight is hard to lose and keep off

The body defends its weight

The brain regulates body weight through a complex system of signals from fat tissue, the gut and the nervous system. When weight falls, this system responds as if food were scarce.

A widely cited study published in the New England Journal of Medicine in 2011 followed people who had lost weight on a very low calorie diet. A year later, levels of several appetite-related hormones remained changed in a direction that would increase hunger, and participants reported feeling hungrier than before they lost weight. Other studies have found that energy expenditure can fall by more than would be expected from the weight loss alone, an effect sometimes called metabolic adaptation.

Genes and environment

Twin and family studies show that genetics strongly influence body weight. Many genes each have small effects on appetite, fullness and how the body stores energy. Rare single-gene forms of obesity exist and can cause severe obesity from childhood.

Genes act within an environment. Calorie-dense, heavily processed food is cheap, convenient and heavily marketed. Many jobs are sedentary. Sleep deprivation, stress, some medicines (such as some antidepressants, antipsychotics, steroids and diabetes treatments), hormonal conditions and social circumstances all play a part. Changes in the food environment over recent decades, rather than changes in genes, explain the rise in obesity at a population level.

Weight stigma

People living with obesity frequently experience stigma, including in healthcare. Stigma can deter people from seeking help, and experiencing it is linked to poorer mental health and, in some studies, further weight gain. Recognising obesity as a disease with biological drivers is intended in part to reduce blame and improve access to effective care.

The UK approach to treatment

NICE guideline NG246 on overweight and obesity management (2025) brought together and updated earlier NICE guidance. It emphasises a person-centred approach: discussing weight sensitively, understanding the person's goals and circumstances, and tailoring support.

The layers of support

UK weight management services are often described in tiers. The exact structure varies between areas.

Mounjaro adds a new route: NICE TA1026 recommended that tirzepatide be offered in primary care, with a phased rollout starting in June 2025 for people with the highest clinical need, and mandatory wraparound support.

The role of lifestyle support

Diet, physical activity and behavioural support remain the foundation of obesity treatment. They improve health even when weight loss is modest, they help preserve muscle and bone, and they are part of every UK licence for weight loss medicines. A loss of 5% to 10% of body weight can bring meaningful health benefits for many people, such as better blood glucose and blood pressure.

The limitation is that, for many people with obesity, lifestyle changes alone produce modest average weight loss that is difficult to maintain because of the biological responses described above. That is where medicines and surgery come in for some people.

Where medication fits

What modern medicines do

GLP-1-based medicines act on the body's own appetite pathways. They mimic gut hormones that signal fullness to the brain and slow stomach emptying. By counteracting some of the drive to eat, they make it easier to sustain a reduced-calorie diet. Our plain-English guide to what GLP-1 medications are explains how they work.

In major trials, average weight loss with these medicines has been substantially greater than with lifestyle support alone, though results vary widely between individuals:

• In STEP 1, semaglutide 2.4mg produced average weight loss of around 15% over 68 weeks, compared with around 2% on placebo.
• In SURMOUNT-1, tirzepatide at the highest dose produced average weight loss of around 20% over 72 weeks.
• In SELECT, semaglutide reduced the risk of major cardiovascular events in people with obesity and established heart disease.

Our overview of every weight loss medication available in the UK covers all licensed options, including orlistat, liraglutide and the newly licensed tablets.

Treating it like other long-term conditions

If obesity is a chronic disease, it follows that treatment may need to be long term. This is the logic behind comparisons with blood pressure medicines: when blood pressure tablets are stopped, blood pressure usually rises again. Nobody considers the tablets to have failed.

The evidence on stopping GLP-1 medicines supports this comparison:

• In STEP 4, people who had lost weight on semaglutide and were then switched to placebo regained a substantial amount of weight, while those who continued kept losing weight or held steady.
• In SURMOUNT-4, people switched from tirzepatide to placebo similarly regained much of the weight they had lost.
• In the STEP 1 extension, participants who stopped semaglutide at the end of the trial had regained around two-thirds of the weight they had lost within a year, and improvements in risk factors such as blood pressure also tended to reverse.

Our guides to weight regain after stopping and long-term GLP-1 use look at this evidence in detail.

The case for caution

Viewing obesity as a chronic disease does not mean everyone with a high BMI needs medication. There are good reasons for a measured approach:

• Side effects. Gastrointestinal effects are common, and serious effects such as pancreatitis and gallbladder disease, though uncommon, occur.
• Long-term data. These medicines have been used widely for weight management for only a few years. Long-term safety data are still accumulating.
• Muscle and bone. Substantial weight loss can reduce muscle and bone, which matters especially for older adults.
• Cost and access. NHS access is limited and phased. Private treatment involves ongoing costs that vary by provider and dose; we do not list prices, but our price comparison explains what affects cost.
• Not suitable for everyone. Pregnancy, some medical histories and some medicines mean GLP-1 treatment is not appropriate. See our guide to who should not take GLP-1s.

Prescribing decisions belong to a prescriber who can weigh these factors for an individual. Prescription-only medicines should only be supplied after a proper consultation, whether through the NHS or a regulated private provider.

Why even modest weight loss can matter

One consequence of treating obesity as a chronic disease is a focus on health outcomes rather than reaching a particular weight. Research over several decades shows that modest, sustained weight loss can improve many weight-related conditions. The size of benefit varies between people and conditions, and the table below is a general summary rather than a promise of any particular result.

This is part of why NICE guidance encourages discussing what matters to the individual. For one person, the main goal may be controlling diabetes; for another, being able to walk without knee pain.

What good long-term care looks like

Whether you are treated through the NHS or privately, care that reflects the chronic disease model is likely to include:

• A thorough initial assessment, covering medical history, medicines, mental health, eating patterns and personal goals.
• A clear plan, including what treatment involves, how progress will be measured and what happens if it does not work.
• Regular follow-up, with someone checking weight trends, side effects, blood pressure and other relevant measures.
• Support beyond the prescription, such as dietary advice, activity guidance and behavioural or psychological support.
• Coordination with your GP, so that medicines for other conditions can be adjusted as weight changes.
• An honest discussion about stopping, including the likelihood of regain and how to minimise it.

Our guide to the online weight loss consultation explains what a good private consultation should include, and our guide to how to choose an online pharmacy for weight loss sets out the regulatory checks worth making.

Obesity across the life course

The chronic disease model also recognises that needs change over time:

• Children and young people. NICE guidance covers children separately, with a strong emphasis on family-based support. Medicines are used only in limited circumstances under specialist care.
• Pregnancy and planning a family. GLP-1 medicines should not be used in pregnancy or while trying to conceive. See our guide to GLP-1 medication, pregnancy and fertility.
• Midlife and the menopause. Hormonal changes affect fat distribution and muscle. See our guide to GLP-1 medication and the menopause.
• Later life. The priority often shifts to preserving muscle, function and independence. See our guide to GLP-1 medication for people over 65.

Surgery as a treatment for chronic obesity

Bariatric surgery, such as gastric bypass or sleeve gastrectomy, produces the largest and most durable average weight loss of any current treatment and can lead to remission of type 2 diabetes in some people. It also carries surgical risks and needs lifelong follow-up and nutritional monitoring. NICE guidance sets out who may be considered. Our guide to GLP-1 medication vs bariatric surgery compares the two.

Choosing between NHS and private care

Many people now seek treatment privately because NHS access is limited. Private treatment through regulated online pharmacies, online doctor services or clinics can be safe if the provider is properly regulated and carries out a thorough consultation. But it should not replace the wider care your GP provides for weight-related conditions.

Our guide to private vs NHS weight loss treatment compares the routes, and our provider comparison shows how regulated services differ in consultation, monitoring and support.

Living with a long-term condition

Thinking of obesity as a long-term condition can change how people approach it:

• Goals shift from a number to health. Improvements in blood glucose, blood pressure, mobility, sleep and wellbeing are meaningful outcomes, even without large weight loss. Our guide to measuring progress beyond the scales explores this.
• Setbacks are expected. Weight regain is part of the condition's natural course, not a sign of failure. Plans can be adjusted.
• Support is ongoing. As with diabetes or asthma, regular review helps.
• Mental health matters. Emotional eating, depression, anxiety and eating disorders can be part of the picture. Psychological support is a recognised part of specialist weight management.

Common questions about the disease model

Does calling obesity a disease remove personal responsibility?

Recognising biological drivers does not mean behaviour is irrelevant. People with any chronic condition make daily choices that affect it. The disease model recognises that those choices happen against a strong biological and environmental background, and that effective treatment can make them easier.

Does it mean everyone with a high BMI is ill?

Not according to the Lancet Commission framework. It distinguishes people whose excess fat is already harming their health from those at increased future risk. That distinction may influence how treatment is prioritised in future.

Is medication a shortcut?

Licensed medicines work alongside lifestyle changes rather than instead of them. They address the biology of appetite, which is one part of a complex condition. Whether they are appropriate is an individual medical decision.

For related reading, browse our long-term treatment guides, or visit our hubs for weight loss injections and oral GLP-1 tablets.

When to speak to a professional

Speak to your GP or practice nurse if:

• you are concerned about your weight or its effect on your health
• you have symptoms of weight-related conditions, such as excessive thirst, snoring with pauses in breathing, or joint pain
• you have tried to lose weight and want to know what support is available locally
• you are considering private weight loss treatment and want advice on how it fits with your other care
• you have experienced eating that feels out of control, or you restrict food heavily, which may suggest an eating disorder

If you are taking a weight loss medicine, seek urgent medical help (call NHS 111, or 999 in an emergency) if you have severe, persistent abdominal pain that may spread to your back, pain in the upper right abdomen with fever or yellowing of the skin, signs of severe dehydration, or thoughts of harming yourself. You can also contact Samaritans on 116 123 at any time.