8 October 2025

Beware weight-loss drug statistics

The details are more complex than pharma’s pitch suggests

The clinic I’ve joined in Canada holds frequent lunchtime meetings with pharmaceutical sales representatives (PSRs). I gave up meeting PSRs in the UK years ago – regular contact alters doctors’ prescribing behaviour, and not usually for the better. It has posed a dilemma: do I refuse to attend, coming across to new colleagues as a member of the awkward squad, or do I go along and try to withstand the promotional buffeting? I’ve squared the circle by treating it as an opportunity, David Attenborough-like, to study PSRs at close quarters in their natural habit.

It’s easy to see where pharma senses the current pots of gold are. Nigh on half the lunches over the five months since I arrived have been with PSRs promoting GLP-1 receptor agonists (Ozempic, Wegovy, Mounjaro et al) for obesity and type-2 diabetes.

Our epidemics of obesity and type-2 diabetes are being driven by socio-economic forces: the industrialisation of food production and retail; the decline in childhood physical activity; the time- and money-poverty of deprived or just-about-managing lives. There are genetic susceptibilities, certainly, but this is squarely an environmental catastrophe. But that’s not where pharma wants the conversation to go.

These conditions must be categorised as “diseases”, something for drugs, not government policies, to solve. Type-2 diabetes has long been thought of in those terms, and there is a concerted effort to move weight problems on to the same turf with a new mantra: “Obesity is a chronic, relapsing disease.” And “chronic” and “relapsing” imply the need for ongoing treatment. We’re sliding rapidly from two-year trials showing that GLP-1s produce temporary weight loss to a narrative that patients must stay on them for life.

What pharma needs desperately to justify the idea of lifelong treatment is evidence that GLP-1-induced weight loss brings actual clinical benefits. The Select study, published in 2023, detected a reduction in non-fatal heart attacks (MIs) in overweight patients with established cardiovascular disease who were treated with Wegovy for three years. When extolling this, PSRs cite relative risk (RR) – the percentage change in an outcome. Presented like this, the results from Select appear arresting: there was a 28 per cent reduction in non-fatal MI. A simple take-home message to lodge in busy doctors’ minds: Wegovy prevents heart disease.

All medications also cause harm, though, and when discussing these, PSRs flip to talking in terms of absolute risk (AR). For example, Select found a 0.8 per cent increase in absolute risk of hip, thigh and pelvic fractures in females. But what’s a 0.8 per cent risk of harm set against a 28 per cent chance of benefit?

This is a sleight of statistics. RR and AR are as comparable as apples and oranges. Present the data the other way around and the AR reduction for non-fatal heart attacks in Select was just 1 per cent. And the RR for breaking a hip in female patients – a condition with a 20 per cent mortality – shot up by 400 per cent. A 1 per cent chance of benefit set against a 400 per cent risk of harm doesn’t sound such a game-changer.

A different way of expressing drug effects is through the “number needed to treat” (NNT) and the “number needed to harm” (NNH). In Select, the NNT was 100: 100 patients had to be dosed up on Wegovy for three years for one to avoid a non-fatal MI; 99 got no such benefit. Conversely, with side effects ranging from nausea and vomiting through to hip fractures, kidney injury, acute gallbladder disease, allergic reactions and more, only 12 patients had to be given the drug for one to come to harm.

The evidence to date suggests GLP-1s may cause patients and the NHS more problems than they solve, but you wouldn’t suspect that from the marketing. The Health Secretary, Wes Streeting, appears to have been taken in: at the recent Labour Party Conference he endorsed widespread GLP-1 use. Politicians, just as much as doctors, must learn to treat pharmaceutical promotion with a healthy dose of scepticism.

[Further reading: Bereaved families demand the government changes “perverse” scrutiny of stillbirths]