Tirzepatide passes Keytruda as world's best-selling medicine

Eli Lilly's tirzepatide has become the world's best-selling medicine. Combined sales of its two brand names — Mounjaro, approved for type 2 diabetes, and Zepbound, approved for obesity — reached $10.1 billion in the third quarter of 2025, against $8.1 billion for Merck's cancer immunotherapy Keytruda ^[1].

Lilly reported the results on October 30, 2025 ^[1][2]. For the first nine months of the year, tirzepatide sales totaled $24.8 billion, compared with $23.3 billion for Keytruda ^[1]. Merck had claimed the title of maker of the world's best-selling drug since 2023 ^[1]. The milestone belongs to the molecule across both brands, not to Zepbound on its own ^[1].

Where the money came from

In the quarter, Mounjaro brought in $6.52 billion worldwide, up 109% from the same period a year earlier. U.S. Mounjaro revenue was $3.55 billion, up 49%, while revenue outside the U.S. rose to $2.97 billion from $728.0 million a year earlier, driven mainly by volume growth ^[2].

Zepbound, which is sold for weight loss, posted $3.59 billion in worldwide revenue, almost all of it in the U.S., where sales rose 184% to $3.57 billion ^[2]. Year to date, Mounjaro has recorded $15.56 billion and Zepbound $9.28 billion ^[2].

Those two products carried Lilly's overall quarter. Total company revenue rose 54% to $17.60 billion, with worldwide volume up 62% but realized prices down 10%. In the U.S., volume rose 60% while price fell 15% ^[2]. The company raised its full-year 2025 revenue guidance to between $63.0 billion and $63.5 billion ^[2].

Lilly also said it is expanding manufacturing, announcing two new facilities in Virginia and Texas and an expansion of its existing site in Puerto Rico ^[2].

Why it matters for patients

The sales figures are one measure of how many people are now on these drugs and how quickly demand has grown. Mounjaro's revenue more than doubled year over year and Zepbound's nearly tripled ^[2], which reflects far more prescriptions being filled rather than higher prices — Lilly reported that the average price it realized per prescription fell, both in the U.S. and worldwide ^[2].

Those realized prices reflect rebates and discounts negotiated with insurers and pharmacy benefit managers, not the amount any individual patient pays. What patients actually pay at the pharmacy counter is not disclosed in these results.

The scale of the market is also driving Lilly's spending on production capacity. The company pointed to new plants in Virginia and Texas and an expanded Puerto Rico site as part of its effort to keep up with demand ^[2]. The results do not say whether that added capacity will change availability or cost for patients, and no timeline for those facilities was given.

Tirzepatide is one of two GLP-1-based medicines competing in this market. Sales figures for semaglutide, sold by Novo Nordisk as Ozempic, Wegovy and Rybelsus, do not appear in these results and were not compared here.

What happens next

Lilly said orforglipron, its experimental oral GLP-1 pill, succeeded in four Phase 3 trials across type 2 diabetes and obesity, and that it plans to submit the drug to global regulatory authorities by the end of the year for the treatment of obesity ^[2]. Whether or when that pill would reach the U.S. market has not been disclosed. Lilly also expects full-year 2025 revenue between $63.0 billion and $63.5 billion, with fourth-quarter results to come ^[2].