Biogen (BIIB) Q4 2025 earnings review
Transition Pains: MS Erosion Outpaces Growth Engines
Biogen's narrative of a successful pivot hit a speed bump in Q4. While full-year numbers met targets, the fourth quarter revealed the harsh reality of the 'Old Biogen' declining faster than the 'New Biogen' can grow. Revenue fell 7% YoY to $2.28B, driven by a sharp 14% drop in the high-margin MS franchise and a surprising 15% drop in Spinraza. While Leqembi (+54%) and Skyclarys (+30%) are growing, they are not yet large enough to offset the legacy drag. GAAP results swung to a loss due to BD charges, and 2026 guidance points to another year of revenue contraction.
🐂 Bull Case
The 'Growth Portfolio' (Leqembi, Skyclarys, Zurzuvae, Vumerity) is working. These products generated ~$800M in Q4 and grew 19% for the full year. Leqembi global sales are up 54% YoY, and Skyclarys grew 30%.
The pipeline is maturing rapidly. Litifilimab (Lupus) has breakthrough designation with data expected late 2026, and Felzartamab is advancing. The company is actively rebuilding its early-stage assets through disciplined BD.
🐻 Bear Case
The MS franchise is eroding faster than anticipated, down 14% in Q4 (vs -7% for FY25). With Tecfidera generics in Europe and Tysabri biosimilars looming, this cash cow is drying up quickly.
Spinraza revenue fell 15% YoY in Q4. While management blamed 'shipment timing,' this creates uncertainty in a competitive SMA market against oral alternatives and gene therapies.
⚖️ Verdict: ⚪
Neutral/Hold. The strategic pivot is the right move, but the timing is messy. The decline of the legacy business is currently overpowering the growth of new launches. Until Leqembi and Skyclarys achieve critical mass, top-line growth will remain elusive.
Key Themes
MS Franchise Deterioration
Decelerating. The decline in Multiple Sclerosis revenue accelerated significantly in Q4 to -14% YoY, compared to a -7% decline for the full year. Tecfidera (-15% YoY) is facing generic pressure in Europe, and Tysabri (-4% YoY) faces biosimilars. This segment still generates ~$917M/quarter, so accelerated erosion acts as a massive anchor on total company performance.
Leqembi Slow-Roll Continues
Accelerating. Leqembi recorded $134M in global in-market sales (+54% YoY). While growing, the pace is linear rather than exponential. Management highlighted the upcoming subcu maintenance approval (PDUFA May 2026) and blood-based diagnostics as keys to unlocking broader adoption, but emphasized that full reimbursement for the subcu pen won't hit until 2027.
Spinraza Shock
Reversing. Spinraza revenue dropped 15% YoY to $356M in Q4, a sharp reversal from growth seen in previous quarters (e.g., +2% in 24Q4). Management cited 'timing of shipments outside the U.S.' as the primary culprit, but admitted full-year revenue was down 2%. The high-dose regimen approval (expected April 2026) is needed to defend share against high-efficacy competitors.
Skyclarys & Postpartum Depression Expansion
Stable/Growth. Skyclarys grew 30% YoY to $133M. Zurzuvae (PPD) generated $66M in Q4, up significantly from $23M a year ago. These assets are performing well, with Skyclarys launching in new geographies. However, Skyclarys U.S. revenue ($89M) benefited from a $9M inventory build, implying some softness in Q1 2026 as this draws down.
Cost Discipline vs. BD Spend
Stable. The company remains disciplined on core OpEx (flat guidance for 2026), but GAAP earnings were crushed by $222M in IPR&D charges from Business Development (BD) deals (Vanqua, Dara, Alcyone). This signals a strategic shift: Biogen is willing to take short-term earnings hits to rebuild the early-stage pipeline, which was previously a weakness.
Other KPIs
Decelerating. Down 7% YoY, significantly worse than the FY25 average growth of +2%. This indicates the crossover point where legacy declines overtake launch growth has been hit negatively in Q4.
Decelerating. Down 42% YoY ($3.44 in 24Q4). Even excluding the $1.26 impact from BD deals, operational EPS would have been ~$3.25, still a decline. Margins were compressed by lower revenue leverage.
Stable. While lower than FY24 ($2.7B), the company retains a strong balance sheet with $4.2B in cash/marketable securities, allowing for continued BD activity and potential buybacks.
Guidance
Decelerating. FY25 ended up +2%, so guiding to a decline in FY26 confirms that the MS cliff (expected down mid-teens %) will outweigh the growth portfolio for another year.
Stable. The midpoint ($15.75) is roughly flat to slightly up vs FY25 actual ($15.28). This suggests margin management and buybacks will be used to protect earnings while the top line shrinks.
Key Questions
Spinraza Stability
Management cited 'timing of shipments' for the 15% drop in Spinraza. Was there any underlying demand erosion due to competition, and when does shipment timing normalize?
Leqembi Inflection Point
With the subcu maintenance approval expected in May 2026, do you expect a step-function change in uptake in 2H 2026, or is the reimbursement lag to 2027 going to delay the benefit?
MS Franchise Floor
With MS revenue down 14% in Q4 and guided down mid-teens for FY26, where is the floor? Are we approaching a stable base of patients on Vumerity/Tysabri, or is this a terminal decline to zero?