Eli Lilly has passed Merck to become the maker of the world’s top-selling medicine, ending Keytruda’s long hold on the title. Merck had claimed the leading position since 2023.
Lilly reported that tirzepatide, sold as Mounjaro for type 2 diabetes and Zepbound for obesity, generated $10.1 billion in third-quarter sales. This brings its year-to-date total to $24.8 billion. Merck, meanwhile, said Keytruda earned $8.1 billion in the same period, reaching $23.3 billion for the year so far.
Tirzepatide reached the top at an unusually fast pace. It was approved for diabetes in 2022 and for obesity in 2023. Keytruda, by comparison, became the world’s best-selling drug nine years after approval.
Analysts surveyed by Visible Alpha expect tirzepatide to reach $32.2 billion in sales this year, slightly ahead of Keytruda’s projected $31.8 billion.
Why Tirzepatide Is So Popular
Demand for GLP-1-based drugs is rising rapidly, and tirzepatide has stood out because of how it works. The medicine activates two hormone receptors — GIP and GLP-1 — which help improve insulin response, slow digestion, reduce appetite, and increase feelings of fullness. This dual action is one reason patients often see strong improvements in both blood sugar and weight.
Clinical studies show that tirzepatide can lead to double-digit percentage weight loss, significant drops in HbA1c, and improvements in cholesterol and inflammation levels. Lilly recently reported that the drug reduced the risk of heart-failure-related events by 38% in a major study. Long-term data also suggest that tirzepatide may lower the chance of developing type 2 diabetes in people with prediabetes.
These results have helped Lilly gain an edge over Novo Nordisk, the maker of Ozempic and Wegovy. Although Novo reached the market earlier, many experts now view tirzepatide as the most effective option for weight loss.
Competition Intensifies
The rivalry in the obesity-drug market continued on Thursday when Novo announced a takeover bid for biotech company Metsera. The move came only a month after Metsera said it planned to be acquired by Pfizer, showing how aggressive the competition has become.
Safety and Side Effects
Despite its strong performance, tirzepatide has side effects. The most common problems are nausea, vomiting, diarrhea, and constipation, especially at higher doses. Patients using other diabetes drugs may experience low blood sugar. There are also warnings about possible risks of pancreatitis, gallbladder issues, and certain thyroid tumors, though long-term data are still limited. Because the medicine is injected weekly, some people report mild injection-site reactions.
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