Novo's news lifted shares in Europe's second-most valuable listed company after Louis Vuitton by more than 17% to record highs. They have now surged almost 165% over the past two years.

The results of the late-stage trial may help persuade insurers in the US and health authorities in Europe to cover the cost of Wegovy, which is $1,300 (€1,185) a month in the US, for a wider range of patients.

US law classifies weight-loss treatments as lifestyle drugs. Novo said the eagerly-awaited study results, which have not been peer reviewed, showed patients on Wegovy had a 20% lower incidence of heart attack, stroke or death from heart disease compared to those on a placebo. 

That is significantly better than the 15% to 17% expected by investors and analysts.

The study, called Select, involved 17,500 overweight or obese people with a history of heart disease aged 45 years or older with no prior history of diabetes. It started almost five years ago to test if the weekly injection has medical benefits.

The results will likely stir debate about whether the long-term medical benefits are enough to reduce the overall burden on healthcare systems and the cost of treating heart disease in overweight and obese people.

"I suspect that medical claims savings from this are years away," said Dr Jeff Levin-Scherz, a consultant at Willis Towers Watson, which advises employers on benefits. He said the drugs at best may prove to be cost-effective in terms of improving patients' lives, rather than lowering their total cost of care.

Large US companies who manage their employees' healthcare benefits and traditionally covered weight-loss treatments have scaled back due to spiralling costs.

Still, the landmark trial data shows Wegovy has "the potential to change how obesity is regarded and treated", said Martin Holst Lange, executive vice president for development at Novo, in the statement. 

Novo said it expected to file for regulatory approvals of a label indication expansion for the weekly injection in the EU and the US this year. 

More than half a dozen companies, from Pfizer and Amgen, are working on weight-loss therapies similar to Wegovy, hoping for a slice of a market estimated to be worth as much as $100bn by the end of the decade.

The weekly injection makes patients feel full for longer and leads to an average weight loss of about 15% when combined with changes to diet and exercise. It belongs to a class of drugs known as GLP-1 agonists, originally developed to treat type 2 diabetes. 

Eli Lilly is expected to receive a US weight-loss approval for its similar drug, Mounjaro, later this year. Lilly's shares rose nearly 16%. 

• Reuters