GLP-1 weight-loss injections: Wegovy, Mounjaro and the NHS cost catch

New injectable weight-loss drugs are reshaping waistlines, NHS budgets and expectations – but they carry an uncomfortable catch.

People taking major obesity injections including Wegovy and Mounjaro can shed a remarkable amount of weight. However, when the injections end, weight commonly returns much faster than clinicians and health economists had anticipated.

Weight-loss injections that seemed almost miraculous

Clinical trials have presented weekly treatments such as semaglutide (Wegovy), tirzepatide (Mounjaro) and liraglutide (Saxenda) as transformative. On average, participants lost 15–20% of their body weight – substantially more than is usually achieved through diet and exercise schemes.

The medicines belong to a group known as GLP-1 analogues. They influence hormones involved in appetite regulation and blood-sugar management. Many users report feeling satisfied sooner and spending less time thinking about food.

About one in 50 people in the UK now uses these injections. The majority do not receive them via the NHS: around 90% pay privately, typically spending £120–£250 each month. For many families, this is comparable with taking on a second rent or mortgage payment.

The cost becomes an issue rapidly. More than half of those who begin these medicines discontinue them within 12 months, chiefly because they can no longer pay for them. Doctors previously lacked robust evidence about what followed. A new British Medical Journal analysis has now addressed that gap, with sobering results.

Clinical data suggest that, once treatment stops, people regain almost all the weight they lost within about 18 months.

Weight returns – and returns quickly

A review of the available trials identified a consistent trend. Participants who stopped GLP-1 injections gradually regained weight. Within around 18 months, most had returned to, or close to, their original weight.

The rate of this return is notable. People stopping injections regain weight roughly four times faster than those who lose it through structured nutrition and physical-activity programmes.

The health improvements that initially made these treatments appealing to healthcare services also diminish. During treatment, patients commonly experience:

• lower blood pressure
• improved cholesterol levels
• better blood sugar control

After the injections are discontinued, these measures move back towards their pre-treatment levels. This poses difficult questions for a health service primarily funding the medicines to avoid heart attacks, strokes and complications from diabetes.

The health gains seem tightly tied to staying on the injection; stop the drug, and the numbers slide back.

Long-term treatment or a temporary boost?

The evidence points to an uncomfortable possibility: many people may need to remain on obesity injections for the long term, perhaps for life, to retain both the weight loss and the associated health gains.

Some private providers seek to soften this reality by combining injections with intensive lifestyle support, including frequent coaching, eating plans and exercise advice. The BMJ analysis found that this support produced an additional average weight loss of 4.6 kg while treatment continued.

However, there is no persuasive evidence that extra coaching during or after treatment reduces the pace of weight regain once the medicine is withdrawn. Patients and clinicians are therefore left with a difficult decision: keep paying or prepare for weight to return.

Who can access GLP-1 injections – and who cannot?

Obesity is not distributed evenly across the population. It is more common in deprived areas, where sedentary work, inexpensive calorie-dense food and restricted access to green space can coincide. These are also the communities least likely to be able to finance private treatment.

The NHS is introducing GLP-1 injections, although eligibility rules are strict. They are currently available only to people with severe obesity – generally a body mass index (BMI) above 40 – who also have at least one serious obesity-related health condition, such as high blood pressure or type 2 diabetes.

As a result, many people whose weight is high enough to harm their health, but not high enough to meet current NHS thresholds, are largely shut out unless they can fund treatment themselves. For them, these new medicines are more an indication of what may be possible than a practical choice.

Cost-effectiveness model under strain

The National Institute for Health and Care Excellence (NICE) approved these medicines for NHS use using cost-effectiveness models. Those calculations assumed a two-year treatment period followed by gradual weight regain over roughly three years once treatment ended.

The latest evidence calls those assumptions into question. If most weight returns within 18 months, while blood pressure and cholesterol also worsen at a similar pace, the value of a short treatment course appears considerably lower than NICE first estimated.

Faster regain means fewer years of better health for every pound spent, which changes the maths for the NHS.

Keeping patients on treatment indefinitely could maintain the benefits, but would be costly. Future generic versions or tablet formulations may eventually reduce prices, yet they are unlikely to become cheap soon. Health economists must now reassess the figures using real-world patterns of starting and stopping treatment rather than neat clinical-trial schedules.

Traditional programmes still have a role

Conventional weight-management services remain the principal option for people who do not qualify under NHS criteria or cannot afford private prescriptions.

One method receiving fresh attention is “total diet replacement”: nutritionally complete soups and shakes replace ordinary food for 8–12 weeks, followed by a planned reintroduction of meals. Such programmes can deliver weight loss comparable with that achieved by GLP-1 medicines, for a much smaller cost.

Group services including WeightWatchers and Slimming World produce more modest average losses, but are generally less expensive per participant. Research indicates that they can still offer the NHS good value, especially when they prevent or postpone type 2 diabetes.

What GLP-1 actually means

GLP-1 means “glucagon-like peptide-1”. It is a hormone released by the gut after a meal, telling the brain that the body is full and slowing the passage of food through the stomach.

Medicines such as semaglutide imitate this hormone. They suppress appetite and may alter how the brain’s reward system responds to food, helping explain why many people say they have fewer cravings. They also enable the pancreas to release insulin in a more regulated manner, stabilising blood sugar.

When injections cease, these signals diminish. The body’s existing appetite and energy-balance mechanisms regain influence, often strongly. For those who have experienced obesity for many years, these biological pressures can be powerful, potentially explaining the swift weight regain recorded in trials.

Real-life scenarios: what patients are facing

Take a 45-year-old office worker with obesity and high blood pressure. While receiving a GLP-1 injection, she loses 20 kg in a year, her blood pressure returns to normal and she stops taking one of her medicines. After 12 months, private prescriptions become unaffordable, so she discontinues treatment. During the following 18 months, she regains most of the 20 kg. Her blood pressure rises again, along with the heart-disease risk that the NHS had briefly lowered.

A second patient has a comparable weight but no major complications, placing him just below the NHS eligibility threshold. Through his GP, he undertakes a 12-week total diet replacement programme. He loses slightly less weight than a neighbour using injections, but spends far less. Should continuing support help him maintain even part of that loss, the long-term benefits to the health service could match those of the medicines at a far lower cost.

Risks, benefits and combined approaches

GLP-1 injections are not miracle cures, though they can be highly effective tools. They are especially valuable for people with severe obesity and serious related conditions, where prompt and considerable weight loss may quickly lower the risk of heart disease and diabetes complications.

Adverse effects must also be considered. Many users experience nausea, vomiting, diarrhoea or constipation, particularly as doses are increased. Most symptoms can be managed, although some patients end treatment because they feel unwell.

Some specialists are exploring combined strategies: using GLP-1 medicines to initiate weight loss before moving patients to intensive lifestyle programmes as the dose is reduced, with the aim of slowing the rebound. Evidence supporting this phased method remains limited, but it signals wider thinking that injections should not be viewed as isolated miracles, but as one part of longer and more complicated obesity care.

For patients and healthcare systems, the message is stark. These medicines are effective while they are being taken and can produce impressive changes on the scales. Once injections stop, biology responds swiftly, and the cost of sustained treatment is only beginning to be understood.