What the label lists and what reports show
Tofersen side effects
Tofersen's FDA label: “The most common adverse reactions ( ≥ 10% of patients treated with QALSODY and greater than placebo) were pain, fatigue, arthralgia, cerebrospinal fluid white blood cell increased, and myalgia.” FAERS holds 503 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 (52 reports).
- No generic listed
Check it at the source: the tofersen FDA label on DailyMed (effective November 13, 2024, Biogen Inc.); the FDA FAERS public dashboard.
What does the label list?
From the label: adverse reactionsThe most common adverse reactions ( ≥ 10% of patients treated with QALSODY and greater than placebo) were pain, fatigue, arthralgia, cerebrospinal fluid white blood cell increased, and myalgia.
Table 1: Adverse Drug Reactions That Occurred in At Least 5% of Patients Treated with QALSODY and at >5% Higher Frequency Than Placebo
| Reaction | Adverse Reaction QALSODY 100 mg (n = 72) % | Study 1 Part C Placebo (n = 36) % |
|---|---|---|
| Pain | 42 | 22 |
| Fatigue | 17 | 6 |
| Arthralgia | 14 | 6 |
| CSF white blood cell increased | 14 | 0 |
| Myalgia | 14 | 6 |
| CSF protein increased | 8 | 3 |
| Musculoskeletal stiffness | 6 | 0 |
| Neuralgia | 6 | 0 |
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 clinically significant adverse reactions are discussed elsewhere in the labeling: Myelitis and/or Radiculitis [see Warnings and Precautions ( 5.1 )] Papilledema and Elevated Intracranial Pressure [see Warnings and Precautions ( 5.2 )] Aseptic Meningitis [see Warnings and Precautions ( 5.3 )] The most common adverse reactions ( ≥ 10% of patients treated with QALSODY and greater than placebo) were pain, fatigue, arthralgia, cerebrospinal fluid white blood cell increased, and myalgia. (Section 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact Biogen at 1-877-725-7639 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 QALSODY cannot be directly compared to rates in clinical trials of other drugs and may not reflect the rates observed in practice. The safety of QALSODY 100 mg was evaluated in 147 patients with SOD1-ALS. The median patient exposure was 119.4 weeks (range from 4 to 212 weeks). QALSODY was evaluated in the placebo-controlled Study 1 and in the open label extension Study 2. In Study 1 Part C, approximately 43% were female; 57% were male; 64% were White and 8% were Asian. The mean age at entry in Study 1 Part C was 49.8 years (range from 23 to 78 years). …
Source: FDA drug label, Biogen Inc., effective November 13, 2024 (SPL set 81356b45-1cb7-4eef-88ea-e44cc18b47c5), via openFDA; the full label on DailyMed
What do FAERS reports show?
503 reports list tofersen among the medicines taken, each a report of something that happened, not proof the medicine caused it; 105 are coded as a death and 128 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, 7 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?
- Tofersen: the full record
- label, generics, price, shortages, recalls
- Report a side effect to the FDA
- MedWatch
- Side effects hub
- the most reported medicines and reactions