Welcome to the healthier, happier world of 2030. Heart attacks and strokes are down 20%. A drop in food consumption has left more money in people’s wallets. Lighter passengers are saving airlines 100 million litres of fuel each year. And billions of people are enjoying a better quality of life, with improvements to their mental and physical health.

These are just some of the ways in which analysts forecast that the new wave of incredibly effective weight-loss drugs, known as GLP-1 agonists, might transform societies and save countries trillions of dollars in the long run. The best known is semaglutide, marketed as Ozempic for diabetes, and as Wegovy for weight loss.

It might have already started. In the United States, where 12% of adults say that they have at some stage taken GLP-1 agonists for diabetes or weight loss (see ‘Uptake of GLP-1 drugs in the United States’), media reports suggest that obesity rates are falling, although scientists caution that the data are not statistically significant (see ‘US obesity rates’). Slowing or reversing obesity trends more widely — more than half of the world’s population is expected to be overweight or have obesity by 2035 — would have myriad ripple effects.

But although scientists agree that the drugs could have huge impacts, there is a lot of uncertainty. Efforts to model the weight-loss drugs’ future impact are highly speculative for various reasons, ranging from their high costs to their long-term biological effects, and the big unknown of how people’s behaviour will change. All that has medical researchers and companies scrambling to gather more data and develop better tools to assess how weight-loss drugs might transform societies.