Collaborative and Other Relationships (Tables)

3 Months Ended

Mar. 31, 2026

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Co Promotion Profit Sharing Formula

Our share of the combined annual co-promotion profits for RITUXAN and LUNSUMIO in excess of $50.0 million varies upon the following events, as summarized in the table below:

After LUNSUMIO Approval until the First Threshold Date	37.5	%
After First Threshold Date until the Second Threshold Date	35.0	%
After Second Threshold Date	30.0	%

Summary of Activity Related to BAN2401 and Elenbecestat Collaboration

A summary of development and sales and marketing expense related to the LEQEMBI Collaboration is as follows:

	For the Three Months Ended March 31,
(In millions)	2026		2025
Total development expense incurred by the collaboration related to the advancement of LEQEMBI	$	69.3	$	52.6
Biogen's share of the LEQEMBI Collaboration development expense reflected in research and development expense in our condensed consolidated statements of income	34.6		26.3
Total sales and marketing expense incurred by the LEQEMBI Collaboration	169.5		177.7
Biogen's share of the LEQEMBI Collaboration sales and marketing expense reflected in selling, general and administrative expense in our condensed consolidated statements of income	84.7		88.8

Summary of activity related to the UCB collaboration

A summary of development expense related to the UCB collaboration agreement is as follows:

	For the Three Months Ended March 31,
(In millions)	2026		2025
Total UCB collaboration development expense	$	29.4	$	21.8
Biogen's share of the UCB collaboration development expense reflected in research and development expense in our condensed consolidated statements of income	14.7		10.9

Summary of Activity Related to Sage Therapeutics

A summary of development and sales and marketing expense related to the Supernus collaboration is as follows:

	For the Three Months Ended March 31,
(In millions)	2026		2025
Total Supernus collaboration development expense	$	1.2	$	2.4
Biogen's share of the Supernus collaboration development expense reflected in research and development expense in our condensed consolidated statements of income	0.6		1.2
Total sales and marketing expense incurred by the Supernus collaboration	47.5		43.5
Biogen's share of the Supernus collaboration sales and marketing expense reflected in selling, general and administrative expense and collaboration profit sharing/(loss reimbursement) in our condensed consolidated statements of income	23.7		21.7

Summary of Activity Related to Denali Therapeutics Collaboration

A summary of development expense related to the Denali collaboration is as follows:

	For the Three Months Ended March 31,
(In millions)	2026		2025
Total Denali collaboration development expense	$	10.3	$	12.8
Biogen's share of the Denali collaboration development expense reflected in research and development expense in our condensed consolidated statements of income	6.2		7.7

Summary of Activity Related to Stoke Therapeutics Collaboration

A summary of development expense related to the Stoke collaboration agreement is as follows:

	For the Three Months Ended March 31,
(In millions)	2026		2025
Total Stoke collaboration development expense	$	12.2	$	3.9
Biogen's share of the Stoke collaboration development expense reflected in research and development expense in our condensed consolidated statements of income	3.7		1.2