Eli Lilly said on Wednesday patients taking its obesity drug Zepbound lost 47% more weight than those who were given Novo Nordisk's Wegovy in the first large, head-to-head trial of the highly in-demand rival medicines.

In the 751-person trial, Zepbound helped patients lose an average of 20.2% of their weight after 72 weeks compared to 13.7% for the group treated with Wegovy, Lilly said.

Participants were either obese or overweight and had an additional related health issue such as obstructive sleep apnea or heart disease. None of the trial subjects had diabetes.

The data comparing the wildly popular medicines shows for the first time that when trial parameters are exactly the same, Lilly's drug is more effective for weight loss.

U.S. approvals for the medicines was based on separate trials in which Zepbound helped patients lose more than 22% of their overall weight after 72 weeks, while Wegovy led to a 15% weight loss after 68 weeks.

Doctors had been prescribing these drugs based on whichever was available to patients at the pharmacy given intermittent supply shortages.

The most common side effects for both the drugs were related to the gastrointestinal system and were generally mild-to-moderate in severity, Lilly said.

The results may persuade insurers in the U.S. and cost-conscious health authorities in Europe to give preferential coverage to Zepbound over Wegovy, as health authorities in Britain considered doing earlier this year before approving Lilly's drug.

An analysis of health records and other data published by the medical journal JAMA Internal Medicine earlier this year showed Zepbound led to faster and greater weight loss than Wegovy.

U.S.-based Lilly and Danish rival Novo Nordisk have been in a race to get their obesity drugs approved to treat other ailments to help improve acceptance by insurers and governments.

Wegovy was approved in the US as a treatment for heart disease in March, while Zepbound is expected to be given the green light as a treatment for obstructive sleep apnea.

Both drugs are sold in the U.S. under different brand names - Novo's Ozempic and Lilly's Mounjaro - to treat Type 2 diabetes.