December 9, 2023

Eli Lilly on Thursday announced that its new experimental weight-loss drug caused clinical trial patients with obesity to lose up to 22.5% of their body weight, or more than 50 pounds.

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Clinical trial results

In a recent study, Eli Lilly’s experimental obesity drug—a weekly injection called tirzepatide—helped clinical trial patients lose roughly one-fifth of their body weight.

When Eli Lilly’s SURMOUNT-1 trial began, the study’s 2,539 participants weighed 231 pounds and had a BMI of 38, on average. Most of the participants did not qualify for bariatric surgery, which is reserved for people with a BMI higher than 40, or those with a BMI from 35 to 40 who also have sleep apnea or Type 2 diabetes. 

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For the 72-week trial, participants who received the two highest doses of the drug and followed a diet and exercise program lost an average of about 52 pounds. In comparison, participants who followed the same diet and exercise plan with a placebo lost just five pounds on average.

At the end of the trial, participants who received the high doses of tirzepatide weighed, on average, about 180 pounds with a BMI just under 30—results that far surpass those typically seen in weight-loss medication trials, where diet, exercise, and obesity drugs typically yield closer to 10% weight loss. This level of weight loss is typically seen only in surgical patients, the New York Times reports.

Because obesity is a chronic medical condition, patients would need to take tirzepatide for a lifetime.

According to Louis Aronne, director of the comprehensive weight control program at Weill Cornell Medical Center and the principal investigator for the study, some participants even lost enough weight to fall into the normal range.

Notably, participants seemed to tolerate the drug well, which is a key characteristic in a field where negative side effects often cause people to stop taking drugs, the Washington Post reports.

A spokesperson for Eli Lilly said the company does not yet have a public timeline for seeking FDA approval for tirzepatide.

However, if the results hold up in additional trials and the drug receives FDA approval, many experts believe it could make a sizable impact in the market, and have significant growth potential, the Post reports.


While the company has not yet submitted the trial data for publication in a peer-reviewed medical journal or presented them in a public setting, the initial results amazed many medical experts.

Lee Kaplan, an obesity expert at the Massachusetts General Hospital who was not involved in the trial or development of tirzepatide, said that the drug’s effect “appears to be significantly better than any other anti-obesity medication that is currently available in the U.S.” The results, he added, are “very impressive.”

Another popular anti-obesity drug, semaglutide, which released last year by Novo Nordisk, resulted in average weight loss of around 15% of body weight.

Separately, Sekar Kathiresan, CEO of Verve Therapeutics, who has no ties to Eli Lilly or the drug, wrote in a tweet, “Wow (and a double Wow!)” According to Kathiresan, drugs like Eli Lilly’s are “truly going to revolutionize the treatment of obesity!!!”

“Obesity is a chronic disease that often does not receive the same standard of care as other conditions, despite its impact on physical, psychological and metabolic health, which can include increased risk of hypertension, heart disease, cancer and decreased survival,” Aronne said.

“Tirzepatide delivered impressive body weight reductions in SURMOUNT-1, which could represent an important step forward for helping the patient and physician partnership treat this complex disease,” he added. (Oshin, The Hill, 4/28; Kolata, New York Times, 4/28; Jarvis, Washington Post, 4/29)


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