Biosimilars Investing: The $30B Patent Cliff

You owned a stock that dropped 15% in a day because “biosimilar competition is coming,” and you had no idea what that meant or whether the fear was priced in. Most biotech investors learn about biosimilars the hard way, after the drop. The problem: you’re reacting to a headline instead of anticipating a cliff that was visible years in advance.

The solution: learn how the biosimilar pathway works and how to calculate the exclusivity clock on any biologic you own. Once you can spot the cliff, you stop being the person who sells into it.

Step 1: Stop confusing biosimilars with generics

Biosimilars are not generics. Generics copy small-molecule drugs and launch at 80-90% discounts. Biosimilars copy biologics, which are grown in living cells, not synthesized in a lab, so no two batches are identical and the copy is never exactly the same molecule. They are approved under the BPCIA (Biologics Price Competition and Innovation Act), under which the FDA requires the copy to be highly similar to the reference product with no clinically meaningful differences. Because of that complexity, a biosimilar costs $100-250 million and 7-8 years to develop, versus roughly $1-5 million and a couple of years for a generic. The result: biosimilars launch at 30-50% discounts, not 80%.

This is the key number in the guide. The originator biologic keeps 50-70% of its list price for years after biosimilar entry, which is why biologics have longer, slower-eroding revenue tails than pills. The full application-type distinction is in the BLA vs NDA guide.

Step 2: Calculate the 12-year exclusivity clock

Every biologic gets 12 years of regulatory exclusivity from its first BLA approval under the BPCIA (4 years of data exclusivity plus 8 more before a biosimilar can win approval). That’s the floor. From the approval date, you can estimate the earliest possible biosimilar entry: approval year plus 12.

The clock is the floor, not the ceiling, because patents usually extend it. But knowing the floor lets you rank which biologics in your portfolio are closest to the cliff. A biologic approved in 2016 is already past its 12-year regulatory mark and is exposed whenever the patent thicket finally cracks.

Step 3: Don’t trust the patent date, read the thicket

Patent expiries on biologics are rarely a single clean date. The originator builds a thicket of composition, formulation, and method-of-use patents, and settles with would-be biosimilar makers to delay entry.

Humira is the case study. Its core US composition patent expired in 2016, but AbbVie’s thicket of more than a hundred patents, plus settlements, held off US biosimilars until January 2023. That’s seven extra years of monopoly pricing. When the biosimilars finally arrived, they hit hard. Humira peaked at $21.2 billion in 2022 and had fallen to roughly $3 billion annualized by 2026, with US sales down 47% year over year in the second quarter of 2026. AbbVie survived because Skyrizi and Rinvoq grew to more than $8 billion in combined quarterly revenue, taking the company’s Humira dependence from 39% of revenue in 2022 to 9% in 2025. The lesson isn’t just the cliff. It’s the replacement strategy.

Step 4: Know what “interchangeable” means for pharmacy substitution

An interchangeable biosimilar is one the FDA has approved to be substituted at the pharmacy without the prescriber having to intervene, the way a generic is. It requires extra switching studies showing the patient can go back and forth without a safety or efficacy problem. Interchangeability matters because it’s what actually drives volume, and it’s what pharmacy benefit managers use to force switching. A biosimilar that isn’t interchangeable needs the doctor to write a new prescription, which slows uptake. The FDA’s Purple Book lists every approved biologic and biosimilar, including which ones are interchangeable, so you can check the competitive field for any drug in two minutes.

Step 5: Price the 2028-2031 wave into your holdings

The next wave is bigger than Humira. Keytruda, the world’s best-selling drug at $29.5 billion in 2024 (56% of Merck’s revenue), loses its core US composition-of-matter patent in 2028, putting more than $25 billion of annual revenue in the path of biosimilars, with Samsung Bioepis, Celltrion, and at least six others already in development. Opdivo at $9 billion expires the same year. Stelara’s biosimilar erosion is already underway. Dupixent, at $13 billion and growing, faces its cliff in 2031. The full exposure map is in the patent cliff M&A analysis.

When you own an originator, the question is the same one AbbVie answered: does the company have a pipeline that can replace the cliff? Merck’s Keytruda concentration is the opposite of AbbVie’s transition.

Step 6: Layer the IRA on top

Medicare drug price negotiation compounds biosimilar pressure. Biologics get 13 years before they’re eligible for negotiation, versus 9 for small molecules, and Keytruda and Opdivo are already in the 2028 negotiation round. A biologic facing both a biosimilar and a negotiated price cut is a different risk profile than one facing neither. The mechanics are in the IRA drug pricing guide.

Common mistakes

Assuming biosimilars behave like generics. They launch at 30-50% discounts, not 80%, and the originator keeps meaningful share for years. If you short a biologic expecting a generic-style collapse, you’ll be early and wrong.

Trusting the headline patent date. The thicket and the settlements are the real date. Humira’s composition patent expired in 2016 and biosimilars didn’t arrive until 2023.

Ignoring the replacement pipeline. The cliff itself isn’t the trade. Whether the company can grow through it is. AbbVie did; the next wave of companies may not.

Selling after the headline. By the time “biosimilar competition is coming” is in the news, the cliff has usually been priced for months.

Final checklist

• Biologic identified as a BLA, not an NDA (see the BLA vs NDA guide)
• 12-year exclusivity clock calculated from first approval
• Patent thicket checked (composition, formulation, method-of-use, settlements)
• Interchangeable biosimilars already approved or pending
• Replacement pipeline assessed (can the company grow through the cliff)
• IRA negotiation eligibility checked (13-year biologic clock)
• Position sized for a 15-25% drawdown on the first biosimilar headline