A prescription for Mounjaro costs roughly £200 a month. A weekly shop that actually supports the body through rapid weight loss, plenty of protein, fresh vegetables, the micronutrients you stop getting once your appetite falls off a cliff, costs more than the cheap, calorie-dense food it is meant to replace. For a household already choosing which bills to skip, that second cost is the one nobody prescribes. And it may be the one that decides whether the drug works.
That is the uncomfortable argument three researchers put to Nature Medicine this week. Their case is not that semaglutide and tirzepatide, the active ingredients in Wegovy, Ozempic and Mounjaro, fail to do what the trials promised. They plainly do. The worry is what happens after the prescription, in the part of treatment that takes place in kitchens and supermarkets rather than clinics.
The scale here is no longer niche. Around 1.6 million adults across England, Wales and Scotland used this class of drug to lose weight between early 2024 and early 2025, and another 3.3 million told researchers they would like to try it within the year. A medicine that a few years ago felt like a celebrity rumour is now something millions of ordinary people are either taking or queuing up for.
Marie Spreckley, who led the correspondence from the University of Cambridge, thinks the public conversation has been asking a slightly wrong question. “The key question is not simply who can access these medications, but who can benefit from them in the long term,” she says. “If access to healthy food, nutrition support and ongoing care is uneven, there is a risk that the benefits of these treatments will also be uneven.”
Here is the mechanism the authors keep returning to. These drugs work largely by quietening hunger. Appetite drops, portions shrink, and along the way they often bring nausea and a feeling of fullness that arrives after a few mouthfuls. For most patients that is the point. But eating less is not the same as eating well, and the two can pull apart fast. Evidence the team reviewed suggests that when energy intake falls sharply, some people lose muscle as well as fat, which is why protein intake, vitamin and mineral monitoring, and even structured resistance exercise matter, particularly for older adults and post-menopausal women. None of that happens automatically. It takes advice, follow-up, and food you can afford.
The bit that happens after the prescription
And food you can afford is exactly where the argument turns political. UK data the authors cite show healthier diets running at more than twice the cost per calorie of less healthy ones, a gap that has been widening for years. Roughly one in eight British households already experiences food insecurity. So the guidance handed to a patient leaving the clinic, eat more protein, keep your diet varied, look after your micronutrients, quietly assumes a fridge and a budget that a sizeable minority simply do not have.
Senior author Adrian Brown, an obesity researcher at UCL, frames the whole thing as a category error in how we have been talking about these medicines. “We have highlighted that obesity treatment is not just a medical issue, but a social and structural one,” he says. “Without integrated dietary support and attention to food affordability, these medications could deepen existing health inequalities.”
His worry has a specific shape: a two-tier system. On one side, patients who can pay privately or who land in a well-resourced NHS pathway, getting the drug plus the dietitian, the monitoring, the continuity of care. On the other, patients who get a prescription and little else, in the very communities where obesity-related illness already hits hardest and where healthy food is furthest out of reach.
There is a warning from across the Atlantic. In the United States, where these drugs arrived earlier, observational data on people with diabetes found that disadvantaged groups and some minority populations were less likely to be using them despite being clinically eligible. The British system is built differently, with treatment routed through structured NHS pathways rather than sold standalone. But private provision is expanding even as NHS access stays tightly rationed, which is precisely the divergence that lets ability to pay creep into who gets supported and who gets left to manage alone.
Same number on the scales, different story underneath
What makes this hard to spot is that the headline numbers can look fine while the picture underneath quietly deteriorates. Two people might shed the same number of kilograms over the same six months. One did it with good food and proper follow-up; the other did it by eating much less of much the same cheap diet, slowly running down their nutritional reserves. The scales reward both equally. Services that track weight and blood sugar, and little else, would never see the difference. The authors’ fix is not subtle and not free: build funded wraparound care into prescribing, and pair the drugs with targeted food subsidies for people at risk of going hungry. Treat the food and the support as part of the medicine, not an optional extra bolted on if budgets allow.
Cara Ruggiero, the third author, puts the discomfort plainly. “Guidance that assumes everyone can afford and access healthy food risks being unrealistic and inequitable,” she says. The drugs are, by any measure, a genuine advance. Whether they end up narrowing Britain’s stubborn health gap or quietly widening it will not be settled in a trial. It will be settled in the weekly shop.
Source: Spreckley, Ruggiero & Brown, Nature Medicine (2026)
Frequently Asked Questions
Do weight loss drugs like Wegovy and Mounjaro actually work?
Yes. Large randomised trials of semaglutide and tirzepatide have shown substantial, sustained weight loss and real improvements in metabolic health. The argument in this paper is not about whether the drugs work biologically, but about whether everyone who takes them can get the food and support needed to benefit safely over the long term.
Why does food cost have anything to do with a prescription medication?
Because these drugs work by reducing appetite, people eat much less while on them. Eating less makes it easier to end up short on protein and key nutrients, which can mean losing muscle alongside fat. Avoiding that requires a good-quality diet, and healthier food in the UK costs more than twice as much per calorie as less healthy food, putting it out of reach for some patients.
What is the “two-tier system” the researchers are warning about?
It is the risk that some patients get the medication plus comprehensive support, a dietitian, monitoring, continuity of care, while others get little more than the prescription itself. Because private provision is growing while NHS access stays limited, the level of support a patient receives could increasingly depend on what they can pay, deepening gaps that already fall hardest on deprived communities.
Could someone lose weight on these drugs and still end up less healthy?
Potentially, yes, and that is part of the concern. Weight and blood sugar can improve even as overall diet quality slips, so two people losing the same amount of weight might be on very different nutritional paths. Without routine checks on diet and nutrient levels, services focused mainly on the scales would miss it entirely.
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