Eli Lilly said Wednesday that its obesity drug Zepbound resulted in more weight loss than its main competitor. Novo Nordisk‘s Wegovy, in the first head-to-head clinical trial of weekly injections.

The results suggest that Zepbound could be a superior weight loss treatment and could help obese or overweight patients lose an average of 20.2% of their body weight, or about 50 pounds, after 72 weeks in the Phase III trial. Meanwhile, Wegovy helped people lose an average of 13.7% of their weight, or about 33 pounds, over the same period.

Eli Lilly said Zepbound resulted in 47% greater relative weight loss compared to Wegovy in the study. The company added that more than 31% of people who took Zepbound lost at least a quarter of their body weight, compared to only about 16% of people who took Wegovy who lost that much weight.

Separate studies of the drugs, as well as a recent comparative analysis of health records, have also found that Zepbound outperforms Wegovy when it comes to weight loss. A late-stage study of Zepbound showed that it helped patients lose an average of more than 22% of their weight within 72 weeks, while a separate study of Wegovy showed that it resulted in an average weight loss of 15% within 68 weeks.

But Wednesday’s data appears to be the most concrete evidence of Zepbound’s lead, as the study randomly assigned 751 patients to receive the maximum dose of either drug. The study specifically examined obese or overweight patients with at least one weight-related disease, excluding diabetes.

“Given the increased interest in anti-obesity medications, we conducted this study to help healthcare providers and patients make informed decisions about treatment choices,” said Dr. Leonard Glass, senior vice president of global medical affairs at Eli Lilly Cardiometabolic Health, in a press release.

Eli Lilly is still evaluating the results and plans to publish them in a scientific journal and present them at a medical meeting next year.

The most common adverse reactions for both drugs were gastrointestinal in nature and generally mild to moderate in severity.

Zepbound’s greater weight loss is a big advantage for Eli Lilly, which is competing with Novo Nordisk for a larger share of the booming weight-loss drug market. Some analysts expect the space to be worth $150 billion per year by the early 2030s.

Wegovy came to market about two years before Zepbound, which was approved in the United States in late 2023. Still, some analysts believe that with more years on the market, Zepbound has a good chance of becoming the best-selling drug of all time.

According to November data, data analytics firm GlobalData forecasts that Zepbound will generate $27.2 billion in annual revenue by 2030 and Wegovy will post $18.7 billion in annual revenue in the same year.

Demand far outstripped supply for Zepbound, Wegovy and their diabetes counterparts last year, forcing Eli Lilly and Novo Nordisk to pour billions into expanding their production capacity for the shots. Those efforts appear to be paying off, as the Food and Drug Administration now lists all doses of these treatments as “available” in its drug shortage database.

Still, some patients have difficulty accessing the medications due to inadequate insurance coverage for weight loss treatments in the United States. Without insurance or other savings, Zepbound and Wegovy both cost around $1,000 per month.

The treatments work differently.

Zepbound suppresses appetite and regulates blood sugar by activating two gut hormones called GIP and GLP-1. Wegovy activates GLP-1 but does not target GIP, which some researchers say may also affect how the body breaks down sugar and fat.