Lilly's Mounjaro overtakes Keytruda as the world's best-selling drug
Mounjaro's $8.7 billion quarter edged past Keytruda's $7.9 billion, a shift that shows how much US spending now flows to diabetes and weight-loss drugs.
Eli Lilly's Mounjaro generated $8.7 billion in the first quarter of 2026, moving past Merck's Keytruda, which posted $7.9 billion, to become the world's best-selling medication [1]. It is the first time a diabetes and weight-loss medicine has held that position, and it ends a run at the top for Keytruda that began in the first quarter of 2023 [1].
Keytruda, a cancer therapy, took the top spot in early 2023 by displacing AbbVie's Humira, an autoimmune disorder drug [1].
Mounjaro and Lilly's weight-loss drug Zepbound use the same active ingredient, tirzepatide [1]. Counting both together, Lilly's tirzepatide products generated $36.5 billion in 2025, compared with $31.6 billion for Keytruda that year, so Lilly was already selling more than Merck on that combined basis before the first-quarter comparison [1].
Analysts had predicted for years that Lilly's drugs would be among the best-selling medicines of all time, even though they reached the market after Novo Nordisk's Ozempic and Wegovy [1].
Lilly's sales have continued to climb even as copycat medicines were launched during shortages, and despite pressure from the Trump administration's affordability push that pressed on prices in the GLP-1 market [1].
Why it matters for patients
The ranking is based on revenue, which measures how much the health care system spends on a drug, not how well it works for any one person. Mounjaro is a diabetes drug, Zepbound is a weight-loss drug with the same ingredient, and Keytruda is a cancer therapy, so the table compares products used for very different conditions [1].
The size of these numbers helps explain why these medicines get so much attention from insurers, employers and government programs. The report notes that copycat versions appeared during shortages and that an affordability push pressured GLP-1 prices, two forces that can affect what patients are offered and what they pay [1].
How much of Mounjaro's $8.7 billion came from diabetes use rather than other uses has not been reported [1]. Nor is it disclosed how much of the combined tirzepatide total came from Zepbound versus Mounjaro [1].
What happens next
Both companies report earnings quarterly, and the next round of figures will show whether Mounjaro holds the top position or Keytruda retakes it [1]. Whether the copycat supply and the price pressure described in the report change those totals has not been reported [1]. Lilly and Merck have not disclosed dates for their next quarterly reports in this account [1].
Sources
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