Eli Lilly's experimental obesity drug tirzepatide has delivered unprecedented weight loss results in a large-scale clinical trial, with participants losing up to 22.5% of their body weight over 72 weeks. The findings, published in the New England Journal of Medicine on June 4, represent what researchers describe as a potential breakthrough in obesity treatment.
Trial Results Exceed Expectations
The phase 3 study enrolled 2,539 participants who were obese or overweight with additional health conditions such as high blood pressure, high cholesterol, or cardiovascular disease. At the study's start, participants had an average weight of 231 pounds.
Participants receiving the highest 15-milligram dose of tirzepatide lost an average of 52 pounds, representing 22.5% of their body weight. Those on the lowest 5-milligram dose lost 35 pounds on average (16% of body weight), while the 10-milligram group achieved intermediate results. In contrast, participants receiving placebo lost only 5 pounds (2.4% of body weight).
By the trial's conclusion, participants taking the highest dose had an average weight of 179 pounds, according to Eli Lilly. All participants were instructed to reduce their daily calorie intake by 500 calories throughout the study period.
Expert Response and Clinical Significance
The results have generated significant excitement among obesity specialists. Dr. Sekar Kathiresan, a cardiologist, expressed his surprise on Twitter with "Wow (and a double Wow!)" when Eli Lilly first announced the results in April.
Dr. Lee Kaplan, an obesity expert who consults for pharmaceutical companies including Eli Lilly but was not involved in this study, told The New York Times the results were "very impressive" and the drug "appears to be significantly better than any other anti-obesity medication that is currently available in the US."
Jeff Emmick, vice president of product development at Eli Lilly, noted that the results are similar to those seen in weight-loss surgery, though participants in the tirzepatide trials weren't eligible for bariatric surgery.
Drug Mechanism and Administration
Tirzepatide is a once-weekly injection belonging to a new class of medications called incretins, or gut hormones that help curb appetite and make patients feel full longer. The drug is currently under regulatory review for diabetes treatment.
The most common side effects reported in the trial were nausea, diarrhea, vomiting, and constipation.
Market Context and Regulatory Pathway
Eli Lilly CEO David Ricks described the results as a "best-case scenario" for what researchers could have hoped for. "For a long time, medications for obesity have really come up well short of what I think both doctors and patients would find impressive," Ricks told CNBC. "And we know obesity is such a driver of long-term bad outcomes ... also healthcare costs."
Market analysts told Reuters the numbers validated the buzz around tirzepatide, positioning it to be a "dominant player in the obesity market" with the "potential to be a multibillion-dollar product."
The drug's performance significantly exceeds that of currently approved obesity medications. In June 2021, the FDA approved Wegovy, a higher-dose version of Novo Nordisk's diabetes drug semaglutide, for long-term weight management. Patients taking Wegovy lose on average about 15% of their body weight.
Addressing Unmet Medical Need
Dr. Louis J. Aronne, an obesity expert at NewYork-Presbyterian/Weill Cornell Medical Center who participated in the study, emphasized the clinical importance of these findings. "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," Aronne said.
The study represents one of four trials Eli Lilly is conducting on tirzepatide. According to the CDC, 42% of adults in the United States are considered obese, highlighting the significant unmet medical need that tirzepatide could potentially address.
