Tirzepatide, currently approved to treat type 2 diabetes under the name Mounjaro, is taken once a week as an injection.
Eli Lilly said its trial was conducted over a period of 72 weeks on just over 900 overweight or obese participants with type 2 diabetes.
Those who received the highest dosage lost an average of 15.7 percent of their body weight, or 34.4 pounds (15.6 kilograms), the company said, with the most common side effects being mild to moderate gastrointestinal issues such as nausea and diarrhea.
The Indiana-based company said it plans to complete its submission to US authorities "in the coming weeks" and expects "regulatory action as early as late 2023".
Results from a prior clinical trial on obese and overweight participants who did not have diabetes, published in a scientific journal in June 2021, showed an even greater weight loss – around 21 percent.
Like other drugs which have recently become popular for weight loss, tirzepatide mimics the gastrointestinal hormone GLP-1, activating receptors in the brain involved in appetite regulation.
Though Mounjaro has only been approved in the United States since May 2022 for diabetes treatment, some doctors have already been prescribing it to patients for weight loss.
Many specialists view the GLP-1 analogues as a game-changer, as they lead to much greater weight loss than the drugs available until now.
With 40 percent of Americans estimated to be obese, it also represents a potential financial boon for the pharmaceutical industry.
According to Morgan Stanley, the global market for obesity treatments could be worth $54 billion by 2030.
Novo Nordisk is already marketing its weight loss drug Wegovy – which uses another GLP-1-mimicking chemical called semaglutide – in the United States, where it has been approved by the Food and Drug Administration (FDA) to treat obesity since June 2021.
Ozempic, the Danish company's diabetes drug, which also uses semaglutide, has recently experienced periodic supply shortages, after it went viral on social media for its weight loss effects.
Many in the United States also cannot access the drug at the moment due to its high cost – about $1,000 a month and often not covered by insurance.
Experts are concerned that people who are not clearly overweight are using it to lose a few pounds.
The drugs are also designed to be taken over a long period of time, with risks of regaining the weight lost once treatment is stopped.