Revenue

12 Months Ended

Dec. 31, 2025

Revenue from Contract with Customer [Abstract]

Revenue

Note 5: Revenue

Product Revenue

Revenue by product are summarized as follows:

	For the Years Ended December 31,
	2025						2024						2023
(In millions)	United States		Rest of World		Total		United States		Rest of World		Total		United States		Rest of World		Total
Multiple Sclerosis:
TECFIDERA	$	168.5	$	511.2	$	679.7	$	169.2	$	797.9	$	967.1	$	263.1	$	749.4	$	1,012.5
VUMERITY	651.2		95.6		746.8		538.6		89.4		628.0		512.1		64.2		576.3
Total Fumarate	819.7		606.8		1,426.5		707.8		887.3		1,595.1		775.2		813.6		1,588.8
AVONEX	482.9		212.6		695.5		451.3		256.2		707.5		536.7		274.3		811.0
PLEGRIDY	104.9		145.2		250.1		111.4		149.1		260.5		126.2		168.5		294.7
Total Interferon	587.8		357.8		945.6		562.7		405.3		968.0		662.9		442.8		1,105.7
TYSABRI	965.0		700.4		1,665.4		920.0		795.0		1,715.0		997.9		879.0		1,876.9
FAMPYRA(1)	—		1.4		1.4		—		71.7		71.7		—		90.5		90.5
Subtotal: Multiple Sclerosis	2,372.5		1,666.4		4,038.9		2,190.5		2,159.3		4,349.8		2,436.0		2,225.9		4,661.9
Rare Disease:
SPINRAZA	625.5		921.3		1,546.8		625.7		947.5		1,573.2		610.5		1,130.7		1,741.2
SKYCLARYS(2)	310.6		209.9		520.5		301.1		81.4		382.5		55.9		—		55.9
QALSODY(3)	30.1		56.8		86.9		20.9		11.5		32.4		5.8		0.1		5.9
Subtotal: Rare Disease	966.2		1,188.0		2,154.2		947.7		1,040.4		1,988.1		672.2		1,130.8		1,803.0
Biosimilars:
BENEPALI	—		453.2		453.2		—		479.1		479.1		—		438.8		438.8
IMRALDI	—		190.2		190.2		—		213.1		213.1		—		222.1		222.1
FLIXABI	—		52.6		52.6		—		63.2		63.2		—		77.4		77.4
BYOOVIZ	13.0		19.4		32.4		23.0		13.6		36.6		29.2		2.5		31.7
TOFIDENCE	0.7		—		0.7		1.1		—		1.1		—		—		—
Subtotal: Biosimilars	13.7		715.4		729.1		24.1		769.0		793.1		29.2		740.8		770.0
Other:
ZURZUVAE	195.1		—		195.1		72.2		—		72.2		1.6		—		1.6
Other(4)	0.4		1.7		2.1		2.8		7.5		10.3		2.4		7.8		10.2
Subtotal: Other	195.5		1.7		197.2		75.0		7.5		82.5		4.0		7.8		11.8
Total product revenue, net	$	3,547.9	$	3,571.5	$	7,119.4	$	3,237.3	$	3,976.2	$	7,213.5	$	3,141.4	$	4,105.3	$	7,246.7

(1) Effective January 1, 2025, our collaboration and license agreement for FAMPYRA global commercialization rights was terminated.

(2) SKYCLARYS became commercially available in the E.U. during the first quarter of 2024.

(3) QALSODY became commercially available in the E.U. during the second quarter of 2024.

(4) Other includes FUMADERM and ADUHELM.

We recognized revenue from two wholesalers accounting for 28.0% and 15.8% of gross product revenue in 2025, 25.9% and 13.4% of gross product revenue in 2024 and 27.0% and 9.9% of gross product revenue in 2023, respectively.

As of December 31, 2025, two wholesale distributors individually accounted for approximately 25.4% and 15.2% of net accounts receivable associated with our product sales, as compared to 27.2% and 11.7% as of December 31, 2024, respectively.

An analysis of the change in reserves for discounts and allowances is summarized as follows:

	As of December 31, 2025
(In millions)	Discounts		Contractual Adjustments		Returns		Total
Balance, December 31, 2024	$	162.7	$	880.8	$	48.1	$	1,091.6
Current provisions relating to sales in current year	832.4		2,773.1		31.9		3,637.4
Adjustments relating to prior years	2.2		(83.4)		0.7		(80.5)
Payments/credits relating to sales in current year	(728.3)		(1,905.8)		(1.7)		(2,635.8)
Payments/credits relating to sales in prior years	(153.3)		(618.6)		(30.0)		(801.9)
Balance, December 31, 2025	$	115.7	$	1,046.1	$	49.0	$	1,210.8

	As of December 31, 2024
(In millions)	Discounts		Contractual Adjustments		Returns		Total
Balance, December 31, 2023	$	173.3	$	857.1	$	31.6	$	1,062.0
Current provisions relating to sales in current year	824.2		2,687.5		23.6		3,535.3
Adjustments relating to prior years	8.0		(38.7)		14.2		(16.5)
Payments/credits relating to sales in current year	(670.9)		(1,989.7)		(0.6)		(2,661.2)
Payments/credits relating to sales in prior years	(171.9)		(635.4)		(20.7)		(828.0)
Balance, December 31, 2024	$	162.7	$	880.8	$	48.1	$	1,091.6

	As of December 31, 2023
(In millions)	Discounts		Contractual Adjustments		Returns		Total
Balance, December 31, 2022	$	153.8	$	857.7	$	23.5	$	1,035.0
Current provisions relating to sales in current year	735.6		2,720.1		19.0		3,474.7
Adjustments relating to prior years	(0.4)		(38.4)		19.2		(19.6)
Payments/credits relating to sales in current year	(572.9)		(1,944.8)		(2.1)		(2,519.8)
Payments/credits relating to sales in prior years	(142.8)		(737.5)		(28.0)		(908.3)
Balance, December 31, 2023	$	173.3	$	857.1	$	31.6	$	1,062.0

The total reserves above, which are included in our consolidated balance sheets, are summarized as follows:

	As of December 31,
(In millions)	2025		2024
Reduction of accounts receivable	$	210.4	$	154.1
Component of accrued expense and other	1,000.4		937.5
Total revenue-related reserves	$	1,210.8	$	1,091.6

Revenue from Anti-CD20 Therapeutic Programs

Revenue from anti-CD20 therapeutic programs is summarized in the table below. For purposes of this footnote, we refer to RITUXAN and RITUXAN HYCELA collectively as RITUXAN.

	For the Years Ended December 31,
(In millions)	2025		2024		2023
Royalty revenue on sales of OCREVUS	$	1,414.9	$	1,339.5	$	1,266.2
Biogen's share of pre-tax profits in the U.S. for RITUXAN, GAZYVA and LUNSUMIO	420.2		392.0		409.4
Other revenue from anti-CD20 therapeutic programs	25.5		18.4		14.0
Total revenue from anti-CD20 therapeutic programs	$	1,860.6	$	1,749.9	$	1,689.6

Approximately 18.8%, 18.1% and 17.2% of our total revenue in 2025, 2024 and 2023, respectively, was derived from our collaboration arrangements with Genentech. For additional information on our collaboration arrangements with Genentech, please read Note 19, Collaborative and Other Relationships, to these consolidated financial statements.

Alzheimer's Collaboration Revenue

Alzheimer's collaboration revenue consists of our 50.0% share of LEQEMBI product revenue, net and cost of sales, including royalties, as we are not the principal. We began recognizing Alzheimer's collaboration revenue upon the accelerated approval of LEQEMBI in the U.S. during the first quarter of 2023.

For the years ended December 31, 2025 and 2024, we recognized Alzheimer's collaboration revenue of approximately $177.7 million and $59.9 million, respectively, within our consolidated statements of income. For the year ended December 31, 2023, our share of LEQEMBI product revenue, net, was fully offset by our share of cost of sales, including royalties, resulting in a zero net impact to Alzheimer's collaboration revenue within our consolidated statements of income.

For additional information on our collaboration arrangements with Eisai, please read Note 19, Collaborative and Other Relationships, to these consolidated financial statements.

Contract Manufacturing, Royalty and Other Revenue

Contract manufacturing, royalty and other revenue is summarized as follows:

	For the Years Ended December 31,
(In millions)	2025		2024		2023
Contract manufacturing revenue	$	679.4	$	592.1	$	848.2
Royalty and other revenue	53.5		60.5		51.1
Total contract manufacturing, royalty and other revenue	$	732.9	$	652.6	$	899.3

Contract Manufacturing Revenue

Contract manufacturing revenue primarily reflects amounts earned under contract manufacturing agreements with our strategic customers and batches of LEQEMBI related to our collaboration with Eisai.

Royalty and Other Revenue

Royalty and other revenue primarily reflects royalty revenue on biosimilar products from our license arrangements with Samsung Bioepis and royalties we receive from net sales on products related to patents that we have out-licensed.

For additional information on our license arrangements with Samsung Bioepis and our collaboration arrangements with Eisai, please read Note 19, Collaborative and Other Relationships, to these consolidated financial statements.