Patients who took Eli Lilly’s obesity drug Zepbound (tirzepatide) regained weight after stopping treatment, according to a study released by the drugmaker Monday.

Full results from Lilly’s SURMOUNT-4 study were published in The Journal of the American Medical Association and found that participants randomized to placebo following the 36 week lead-in period experienced mean weight regain of 14% at 88 weeks.

Meanwhile, those who continued with the drug for another 52 weeks experienced an additional 5.5% weight reduction.

The results were published less than a week after the drug, which was approved to treat obesity by the Food and Drug Administration in early November, was made available at pharmacies nationwide.

The FDA previously approved tirzepatide to treat type 2 diabetes in 2022 and Lilly has sold and marketed the drug under the brand name Mounjaro.

In a press release accompanying the study’s findings, Lilly sought to underscore the evolving science behind treating obesity and the factors that affect weight loss.

“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, PhD, SVP of product development at Lilly, in a statement. “However, studies like SURMOUNT-4 show that continued therapy can help people living with obesity maintain their weight loss.”

Lilly’s stock finished the day down more than 2% hours after the study results were published.

Lilly is engaged in a competitive, high-stakes battle with Novo Nordisk and other pharma rivals seeking to dominate the popular weight-loss market with a bevy of GLP-1 drugs. 

Outside of their weight loss capabilities, this class of drugs has also shown the potential to improve heart health and reduce the chances of major cardiovascular events, according to multiple studies.

Widespread interest among consumers has led to off-label use of Mounjaro as well as rival GLP-1 products Ozempic and Wegovy, contributing to shortages throughout the end of 2022 and the entirety of 2023, with more expected through 2024.

Still, the products have been solid revenue generators for drugmakers looking for promising treatments in a post-COVID world.

During Q3, Mounjaro generated more than $1.4 billion in revenue for Lilly and the company’s revenue increased 37% year-over-year.