For the first time, a drug has been shown so effective against obesity that patients may dodge many of its worst consequences, including diabetes, researchers reported.

The drug, semaglutide, made by Novo Nordisk, already is marketed as a treatment for Type 2 diabetes. In a clinical trial published in the New England Journal of Medicine, researchers at Northwestern University in Chicago tested semaglutide at a much higher dose as an anti-obesity medication.

Nearly 2,000 participants injected themselves weekly with semaglutide or a placebo for 68 weeks. Those who got the drug lost close to 15% of their body weight, on average, compared with 2.4% among those receiving the placebo.

More than a third of the participants receiving the drug lost more than 20% of their weight. Symptoms of diabetes and prediabetes improved in many patients.

Those results far exceed the amount of weight loss observed in clinical trials of other obesity medications, experts said. The drug is a "game-changer," said Dr. Robert Kushner, an obesity researcher at Northwestern University Feinberg School of Medicine, who led the study. "This is the start of a new era of effective treatments for obesity."

Dr. Clifford Rosen of Maine Medical Center Research Institute, who was not involved in the trial, said, "I think it has a huge potential for weight loss."

For decades, scientists have searched for ways to help growing numbers of people struggling with obesity. Five currently available anti-obesity drugs have side effects that limit their use.

The most effective treatment so far is bariatric surgery, which helps people lose 25-30% of body weight, on average, said Dr. Louis Aronne, an obesity researcher at Weill Cornell Medicine in New York who advises Novo Nordisk. But surgery is an invasive solution and only 1% of those who qualify go through with the procedure.

The semaglutide study confirms what scientists already know, Kushner said: Willpower is not enough. In the new trial, participants who received the placebo and diet and exercise counseling were unable to see any significant difference in their weight.

Semaglutide, which is likely to be expensive, is a synthetic version of a naturally occurring hormone that acts on appetite centers in the brain and in the gut, producing feelings of satiety. A high-dose regimen of the drug has not been studied long enough to know if it has serious long-term consequences. And it is expected that patients would have to take it for a lifetime.

Qiana Mosely, who lives in Chicago, spent years trying to lose weight with diets and drugs, but to no avail. She joined the semaglutide trial and lost 40 pounds, about 15% of her weight.