When patients stopped taking Eli Lilly's weight loss drug Zepbound, they regained much weight, according to new study results.

The study, published in the research journal JAMA, showed that participants with obesity/overweight, who stopped the weekly injection Zepbound (tirzepatide) had a substantial regain of lost weight, whereas continued treatment maintained and augmented initial weight reduction.

The study included a total of 670 participants who were randomised to continue receiving tirzepatide (Zepbound) or switch to a placebo for 52 weeks.

After 36 weeks of the maximum tolerated dose of tirzepatide (10 or 15 mg), adults with obesity or overweight (without diabetes) experienced a mean weight reduction of 20.9 per cent.

But those who switched to placebo experienced a 14 per cent weight regain and those continuing tirzepatide experienced an additional 5.5 per cent weight reduction during the 52-week double-blind period.

"Patients, providers and the public do not always understand obesity is a chronic disease that often requires ongoing treatment, which can mean that treatment is stopped once weight goals are met," said Jeff Emmick, MD, senior vice president, of product development, Lilly, in a statement.

However, the study shows "that continued therapy can help people living with obesity maintain their weight loss," he added.

Zepbound is not alone. Other weight loss drugs like Wegovy from Novo Nordisk as well as its diabetes medication Ozempic have regained weight, raising concerns among health insurers about the high costs involved with long-term coverage of the pricey drugs.

"If you look at the magnitude of the weight gain, they gain back about half the weight they had originally lost over a one-year period of time," lead study author Dr. Louis Aronne, an obesity medicine specialist and professor of metabolic research at Weill Cornell Medicine in New York City, was quoted as saying to CNN.

About 17 per cent of those who stopped Zepbound maintained at least 80 per cent of their original weight loss, the study said. Meanwhile, 9 in 10 of the people who continued Zepbound were able to maintain at least 80 per cent of the weight they lost.