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Biopharma markets tend to settle on two leading drugs
New therapeutic areas typically end up with two leading drugs, because breakthroughs rarely happen in isolation and payer economics make it hard for later entrants to displace the first pair. Sleuth’s January 2025 map shows nine illustrative drug duopolies across neuroscience, oncology and other therapeutic areas, from Leqembi and Kisunla in Alzheimer’s disease to Mounjaro/Zepbound and Wegovy/Ozempic in obesity and type 2 diabetes. Five forces explain the pattern: first-mover advantages, pharmacy benefit manager (PBM) economics, late entrants’ retreat into niche segments, near-simultaneous scientific discovery and incumbents’ follow-on innovation.
Nine duopolies span neuroscience, oncology and other areas
Each pair on the map carries a sell-side peak sales estimate as of January 2025:
- Neuroscience: in Alzheimer’s disease, Leqembi (Eisai and Biogen, $6 billion) and Kisunla (Lilly, $4 billion); in depression, Vraylar (AbbVie, $5 billion) and Caplyta (Johnson & Johnson, $4.5 billion); in tardive dyskinesia, Ingrezza (Neurocrine, $3.5 billion) and Austedo (Teva, $3 billion).
- Oncology: among TROP2 ADCs, Trodelvy (Gilead, $5 billion) and Dato-DXd (AstraZeneca and Daiichi Sankyo, $2 billion); among BCMA CAR-T therapies for multiple myeloma, Carvykti (Legend and Johnson & Johnson, $5 billion) and anito-cel (Arcellx and Gilead, $4.5 billion); among PD-1 inhibitors, Keytruda (Merck, $30 billion) and Opdivo (Bristol Myers Squibb, $8 billion).
- Other areas: in obesity and type 2 diabetes, Mounjaro/Zepbound (Lilly, $70 billion) and Wegovy/Ozempic (Novo Nordisk, $45 billion); in geographic atrophy, Izervay (Astellas, $2 billion) and Syfovre (Apellis, $1.5 billion); in ophthalmology, Eylea (Regeneron, $9 billion) and Vabysmo (Roche, $8 billion).
One pair was still forming: anito-cel remained investigational when Gilead completed its acquisition of Arcellx in April 2026.
The pattern holds from a $1.5 billion geographic atrophy drug to a $70 billion obesity franchise.
First movers and PBMs both reward the incumbent
As long as they are not building market awareness from scratch, first movers have a large advantage: a clear path to new prescriptions and early mindshare, patients who rarely switch once well controlled, and the chance to build the most comprehensive long-term clinical dataset. Most commercial assets also end up with big pharma, which has the relationships and sales engines to run global launches.
PBMs generally prefer incumbents too. First movers capture the most volume while competitors are few, and that volume is sticky. Manufacturers use it to secure preferred formulary status, big pharma can bundle contracts across its portfolio, and a novel drug with little competition can command a premium list price (WAC), which raises the dollar rebate the PBM receives.
So even an equally effective, lower-priced entrant can lose, because without volume the PBM makes more money on the higher-priced incumbent. Sleuth’s analysis of how indication selection dictates commercial strategy works through the same rebate logic.
Late entrants settle for niches, and parallel discovery supplies the second leader
Because of these payer dynamics and other barriers to entry, many late-to-market assets target narrower segments, such as patients refractory to the first movers. That offers an easier path to initial volume but concedes the frontline population, and market leadership, to the incumbents, unless a follow-on entrant proves head-to-head superiority.
The second leader usually arrives early because breakthroughs rarely happen in isolation. This multiple-discovery effect, combined with fast followers that pivot quickly toward new innovations, is why at least two major players typically emerge in a new therapeutic area.
Discovery tends to produce a pair of leaders, and payer economics tend to keep the field from growing much beyond it.
Incumbents keep extending their lead
First movers rarely rest on their advantage. They run many follow-on studies to expand into new indications, find synergistic combinations and improve dosing and convenience. Keytruda is the extreme case: by September 2023, ClinicalTrials.gov listed 1,251 recruiting or active studies involving pembrolizumab, as Sleuth’s Keytruda case study shows. Keytruda’s 2025 sales of $31.7 billion already topped the map’s $30 billion peak estimate.
A challenger has to beat the profile the incumbent will have after years of follow-on data, not the one it launched with.
Duopoly pairs, owners and sell-side peak sales estimates are as of January 2025. The framework is general; later developments are dated in the text and were checked through September 2026.
Frequently asked questions about biopharma duopolies
What are examples of drug duopolies?
Sleuth’s January 2025 map lists nine, including Leqembi and Kisunla in Alzheimer’s disease, Trodelvy and Dato-DXd among TROP2 ADCs, Keytruda and Opdivo among PD-1 inhibitors, and Mounjaro/Zepbound and Wegovy/Ozempic in obesity and type 2 diabetes.
Why do PBMs favor incumbent drugs?
Incumbents have the most volume, and stable patients rarely switch. Manufacturers use that volume to win preferred formulary status, and a higher list price raises the dollar rebate, so a PBM can earn more from a higher-priced incumbent than from an equally effective, cheaper entrant.
Why do new therapeutic areas usually produce two leaders?
Breakthroughs tend to happen in parallel and fast followers pivot quickly, so at least two major players typically emerge. First-mover advantages, PBM economics and late entrants’ retreat into niche segments then limit how many succeed beyond that.
