Lilly launched Prozac in the 1980s, starting a psychiatric franchise that is now generic
Lilly's Prozac is now a generic medicine, while the company's revenue today leans on tirzepatide, which supplied 56% of its 2025 sales [1].
Eli Lilly brought fluoxetine to the U.S. market under the brand name Prozac, a treatment for major depressive disorder that became one of the company's best-known products and a foundation of its psychiatric franchise [1].
Lilly's own company history dates the launch to 1986 [1]. Some published accounts place the U.S. launch in 1988; that two-year difference has not been reconciled publicly. Prozac was one of three psychiatric drugs that gave Lilly commercial success, alongside Cymbalta (duloxetine), launched in 2004, and the antipsychotic Zyprexa (olanzapine), launched in 1996 [1]. All three are now off patent and are manufactured by other companies as generic drugs [1].
By 2000, Prozac was reported to account for roughly a quarter of Lilly's revenue. That figure is not broken out in the company information cited here, and Prozac does not appear among the products Lilly lists as its main revenue drivers today [1]. For scale, Lilly reported $65.18 billion in revenue for 2025, with operating income of $26.30 billion and net income of $20.64 billion [1].
Lilly's business now looks different. Its largest product by revenue is tirzepatide, sold as Mounjaro for type 2 diabetes and Zepbound for weight loss and obstructive sleep apnea, which accounted for 56% of 2025 revenue [1]. Other top sellers include abemaciclib (Verzenio) at 9%, dulaglutide (Trulicity) at 7%, ixekizumab (Taltz) at 6% and empagliflozin (Jardiance) at 5% [1]. In 2024, 67% of revenue came from the United States, 18% from Europe, 3% from Japan and 3% from China [1].
Lilly's history with GLP-1 drugs runs back two decades. The company brought exenatide to market in 2005, the first GLP-1 receptor agonist, and later added tirzepatide, which acts on both GIP and GLP-1 receptors [1]. In November 2025, Lilly became the first health care company to reach a $1 trillion market capitalization [1].
Why it matters for patients
Prozac's path shows how brand-name drugs typically age. After patents expire, other manufacturers can sell the same molecule as a generic, and fluoxetine, duloxetine and olanzapine are all in that category now [1]. Whether today's GLP-1 drugs follow a similar timeline is a separate question: patent terms, formulations and litigation are not addressed in the company information cited here, so no date for a generic GLP-1 has been disclosed.
The revenue mix also shows how concentrated Lilly's current business is. More than half of 2025 revenue came from a single molecule, tirzepatide [1], which is sold only under the brand names Mounjaro and Zepbound. Concentration at that level means manufacturing capacity, supply decisions and pricing for one drug reach a very large share of the company's sales.
For patients, the practical difference between the Prozac era and the GLP-1 era is structural. Fluoxetine is now made by other companies as a generic [1], while tirzepatide is available only under Lilly's brand names. What Lilly spent to develop or launch Prozac, and what it charged for the drug, are not disclosed in the information cited here.
Sources
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