Not only was there a new injectable formula that helped patients to lose up to 24 per cent of body weight in one trial, but the San Diego conference heard of fast progress towards pills that could work as effectively as the Danish group’s Wegovy and Ozempic. The overweight and obese, or at least those that can afford such pills, now have hope.

In the future, obesity might become a chronic condition that can be treated with tablets, as statins and blood pressure drugs have reduced heart attack risk for millions. It will not only be those including Elon Musk, who can pay Wegovy’s US list price of $16,000 per year, who will benefit. Take semaglutide, reduce your appetite, burn more energy and voilà!

But medicines come with health warnings, inscribed in small print on the leaflets contained inside packets, and this generation of medicines will need them. Treatments that mimic the GLP-1 hormone and use allied mechanisms to reduce obesity are having quick results but we cannot yet be certain of their long-term impact. Here are three warnings to consider.

First, they will be expensive for years to come. Many cardiovascular drugs are off patent and cheap enough for insurers and healthcare systems to cover at scale. But diabetes and obesity medicines are early in that journey — Wegovy will be protected until 2032 in the US — and pharma companies are expert at extending exclusivity.

Nor are they meant to be taken for only a short period. Obese people often rebound to their former weights when they cease treatments and diet regimens. The British NHS has placed a two-year limit on injectables as obesity treatments, but what happens then? Pharma companies are preparing for a battle to keep on getting paid.

Investors believe they will win: Morgan Stanley this week suggested that pills will attract people put off by injections, and global obesity drug sales could exceed $50bn by 2030. The number of TikTok videos recounting weight loss stories, and cases of people taking them who are overweight rather than obese, support this view.

Second, no one can be sure how safe long-term obesity treatments will prove to be. Most of the known side effects are modest, if unpleasant — it is common to feel sick — but there are reasons for caution. The Wegovy leaflet warns of thyroid cancer risk, and Pfizer’s shares fell this week after a trial found that one pill it was developing might be unsafe.

There is a chequered history of obesity pills that apparently produced miraculous results later being banned, going back to the amphetamine craze of the 1960s and “fen-phen”, a combination weight loss therapy that the US Food and Drug Administration ordered off the market in 1997. Several other medicines have since gone through the same cycle of hype and failure.

It may be different this time: Wegovy is approved in both the US and Europe, and many other medicines with known side effects (including statins) remain on the market. But the new obesity pills have only passed mid-stage trials, and the ultimate test will come after launch, when more of the world’s 1.3bn people with diabetes or obesity use them.

Third, losing weight is not equivalent to becoming healthier. Many people want to get thinner to look and feel better, which is a fair motive, but the medical purpose of treatment is to make them less prone to illness, from strokes to cancers. That is why doctors prescribe Wegovy, at least in theory.

Ania Jastreboff, director of Yale University’s obesity research centre and lead author on one of this week’s trials, is enthusiastic about the drugs, calling it a “transformational time” for her field when we spoke this week. But she added that “we have to think about how to maximise patients’ health” when treating obesity.

That means ensuring that they consume enough nutrients as their appetites lessen, and they exercise to build muscles. Being lighter has its own benefits — it reduces the strains on joints, for example — but letting drugs do all the work is not enough, appealing though it may be. This is less a moral point than a medical one: you have to make some health changes yourself.

These warnings do not mean we should spurn Wegovy and the other treatments that are coming, including the likely approval of Eli Lilly’s diabetes drug Mounjaro to treat obesity. Having worked so long in the pharmaceutical wilderness in terms of effective treatment, doctors have sound scientific reasons to make the most of a new opportunity.

But when the pent-up demand for a solution to obesity meets an eager pharma industry, there are pitfalls. That has happened repeatedly before and it could occur again. If miracle pills always met their promises, the world would already be healthier.

john.gapper@ft.com

This story originally appeared on: Financial Times - Author:John Gapper