Growth drugs race a patent cliff
- Amgen's 6 key growth drivers made up 70% of Q1 2026 sales and grew 24% in aggregate.
- Prolia and XGEVA fell 32% year over year to $1.1 billion as copycat biologic drugs entered the market.
- Management raised 2026 revenue guidance to $37.1 billion to $38.5 billion after a strong first quarter.
- MariTide is the big pipeline swing, with new Phase 3 studies testing 8-week or 12-week dosing after weekly obesity drugs.
- The IRS dispute is bigger now because the agency is also auditing the 2016 to 2018 tax years.
New drugs must outrun Prolia
Amgen is in a handoff year. Older bone drugs Prolia and XGEVA are losing protection, and biosimilars, which are copycat versions of complex biologic drugs, are now taking share. In Q1 2026, that franchise dropped 32% year over year to $1.1 billion.
The good news is that the rest of the portfolio is doing real work. Amgen said its 6 key growth drivers made up 70% of sales in Q1 2026 and grew 24% in aggregate. That helped management raise full-year 2026 revenue guidance to $37.1 billion to $38.5 billion and non-GAAP EPS guidance to $21.70 to $23.10.
The stock still has a balanced setup. Repatha, EVENITY, TEZSPIRE, rare disease drugs, oncology drugs, and biosimilars can keep the company growing. But the company must prove that Prolia and XGEVA erosion will not eat too much of that growth.
MariTide could change the story if it works. Amgen is testing whether people can switch from weekly obesity injections to MariTide given every 8 or 12 weeks. That convenience could matter, but the study still has to show the drug can compete on weight loss, safety, and staying power.
Patents, factories, and drug sales
Amgen makes money by selling prescription medicines to wholesalers, distributors, and health systems. Most products are biologics, which are drugs made from living cells. They are hard to copy, but once patents expire, biosimilars can pressure both volume and price.
The moat comes from research skill, patents, clinical data, and large-scale biologic manufacturing. A drug company also needs payer access, which means insurance plans and government programs must agree to cover the medicine at a usable price.
The model can break in three main ways. A major drug can lose exclusivity faster than expected. A pipeline drug can fail in trials. Or payers and governments can force lower net prices, which is already a risk for Otezla under Medicare price setting beginning in 2027.
Amgen is also trying a more direct model in the U.S. AmgenNow started with Repatha at a monthly price of $239, aiming to make access simpler and more affordable for patients.
What sells, what could grow
Repatha
Repatha is a cholesterol-lowering drug and one of Amgen's strongest growth drivers. It had $876 million in Q1 2026 sales, up 34% year over year.
EVENITY
EVENITY treats osteoporosis and is helping offset the Prolia decline. It had $562 million in Q1 2026 sales, up 27% year over year.
UPLIZNA
UPLIZNA is part of Amgen's rare disease push. It had $262 million in Q1 2026 sales, up 188% year over year.
TEPEZZA
TEPEZZA treats thyroid eye disease and came with the Horizon deal. It had $490 million in Q1 2026 sales, up 29% year over year.
Prolia and XGEVA
These denosumab bone drugs are still large, but they are now the main headwind. Combined sales were $1.1 billion in Q1 2026, down 32% year over year.
Biosimilars
Amgen also sells biosimilars, which are lower-cost versions of complex biologic drugs. This business helps diversify sales as some of Amgen's own older drugs face biosimilar competition.
MariTide
MariTide is Amgen's late-stage obesity drug candidate. New Phase 3 studies will test switching from weekly obesity drugs to an every 8-week or 12-week schedule.
One reported segment, many drug lines
Amgen reports as one human therapeutics segment. The mix below uses Q1 2026 product sales color from management: 6 key growth drivers at about 70% of sales and the rest of the portfolio at about 30%.
What could break the thesis
Prolia and XGEVA erosion
High impact · High oddsThe denosumab franchise is already shrinking after loss of exclusivity. Prolia and XGEVA sales fell 32% year over year in Q1 2026, and management expects faster erosion through the rest of 2026 as multiple biosimilars launch globally.
Bigger IRS tax dispute
High impact · Medium oddsAmgen is waiting for a U.S. Tax Court decision on its 2010 to 2015 IRS dispute, expected no earlier than the second half of 2026. The risk grew in April 2026 when the IRS also issued a draft notice for the 2016 to 2018 tax years with similar profit allocation claims.
MariTide disappoints
High impact · Medium oddsMariTide is the largest pipeline swing because obesity is a huge market and current leaders dose weekly. A less frequent schedule could help, but only if the drug shows strong weight loss, clean safety, and good patient persistence.
Tavneos regulatory overhang
Medium impact · Medium oddsThe FDA requested a voluntary withdrawal of TAVNEOS in January 2026, and Amgen contested the request. That creates uncertainty for a drug acquired through ChemoCentryx and adds noise to the rare disease story.
Drug pricing pressure
Medium impact · High oddsGovernment and commercial payers keep pushing for lower net prices. Otezla was selected for Medicare price setting beginning in 2027, which Amgen expects to cause further net selling price declines.
In one breath
What is Amgen known for?
Amgen is known for biologic medicines used in bone disease, cancer, heart disease, rare disease, inflammation, and other serious illnesses. Its major current growth products include Repatha, EVENITY, UPLIZNA, TEPEZZA, TEZSPIRE, oncology drugs, and biosimilars.
Why are Prolia and XGEVA a problem for Amgen?
Prolia and XGEVA lost key protection and now face biosimilar competition. Their combined Q1 2026 sales fell 32% year over year to $1.1 billion, and management expects faster erosion during the rest of 2026.
What is MariTide?
MariTide is Amgen's late-stage obesity drug candidate. Amgen is studying whether patients can switch from weekly obesity injections to MariTide on an every 8-week or 12-week schedule.
What is the biggest legal risk for Amgen?
The biggest legal risk is the IRS tax dispute over profit allocation between the United States and Puerto Rico. The 2010 to 2015 case is waiting for a U.S. Tax Court decision, and the IRS is now also auditing the 2016 to 2018 tax years.