What the label lists and what reports show
Nusinersen side effects
Nusinersen's FDA label: “The most common adverse reactions that occurred in at least 20% of SPINRAZA-treated patients who received Low Dose Regimen and occurred at least 5% more frequently than in control patients were: lower respiratory infection and constipation in patients with …” FAERS holds 7,655 reports naming it through July 30, 2026; the reaction reported most often, leaving out the conditions it is used for, product-use terms and outcomes, is headache (539 reports).
- No generic listed
Check it at the source: the nusinersen FDA label on DailyMed (effective March 31, 2026, Biogen Inc.); the FDA FAERS public dashboard.
What does the label list?
From the label: adverse reactionsThe most common adverse reactions that occurred in at least 20% of SPINRAZA-treated patients who received Low Dose Regimen and occurred at least 5% more frequently than in control patients were: lower respiratory infection and constipation in patients with infantile-onset SMA ( 6.1 ) pyrexia, headache, vomiting, and back pain in patients with later-onset SMA […]
Table 2. Adverse Reactions that Occurred in at Least 5% of SPINRAZA Patients and Occurred at Least 5% More Frequently or At Least 2 Times as Frequently Than in Control Patients with Infantile-Onset SMA (Study 1)
| Adverse Reactions | SPINRAZA 12 mg 1 N = 80 % | Sham-Procedure Control N = 41 % |
|---|---|---|
| Lower respiratory infection 2 | 55 | 37 |
| Constipation | 35 | 22 |
| Teething | 18 | 7 |
| Urinary tract infection | 9 | 0 |
| Upper respiratory tract congestion | 8 | 2 |
| Ear infection | 6 | 2 |
| Flatulence | 5 | 2 |
| Decreased weight | 5 | 2 |
Rows and numbers as the label prints them, under its own column headings (the first rows of a longer table where it runs on). A reaction in a trial table is not necessarily caused by the medicine, and trials differ from everyday use.
From the label: adverse reactions, continuedThe following serious adverse reactions are described in detail in other sections of the labeling: Thrombocytopenia and Coagulation Abnormalities [see Warnings and Precautions ( 5.1 )] Renal Toxicity [see Warnings and Precautions ( 5.2 )] The most common adverse reactions that occurred in at least 20% of SPINRAZA-treated patients who received Low Dose Regimen and occurred at least 5% more frequently than in control patients were: lower respiratory infection and constipation in patients with infantile-onset SMA ( 6.1 ) pyrexia, headache, vomiting, and back pain in patients with later-onset SMA ( 6.1 ) The most common adverse reactions in at least 10% of SPINRAZA-treated patients who received High Dose Regimen and occurred at least 5% more frequently than in historic matched sham-control were: pneumonia, COVID-19, pneumonia aspiration, and malnutrition in patients with infantile-onset SMA ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact Biogen at 1-844-477-4672 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. 6.1 Clinical Trials Experience Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of SPINRAZA cannot be directly compared to rates in clinical trials of other drugs and may not reflect the rates observed in practice.
Source: FDA drug label, Biogen Inc., effective March 31, 2026 (SPL set dd70cd5f-b0fc-4ba4-a5ea-89a34778bd94), via openFDA; the full label on DailyMed
What do FAERS reports show?
7,655 reports list nusinersen among the medicines taken, each a report of something that happened, not proof the medicine caused it; 790 are coded as a death and 2,369 as a hospital stay. Counts follow how widely a medicine is used and watched, and they are not a measure of how risky it is. Of the 23 reactions below, 10 are named by the same term (in US spelling) in the label's adverse reactions, warnings or patient leaflet; a reaction the label does not name may still be there under another word, and a report does not show that the medicine caused it.
Reports received each year
The 25 most reported reactions
Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms
What next?
- Nusinersen: the full record
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- Report a side effect to the FDA
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