What the label lists and what reports show
Casimersen side effects
Casimersen's FDA label: “The most common adverse reactions (incidence >20% and at least 5% higher than placebo) were upper respiratory tract infection, cough, pyrexia, headache, arthralgia, and oropharyngeal pain.” FAERS holds 851 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 poor venous access (102 reports).
- No generic listed
Check it at the source: the casimersen FDA label on DailyMed (effective January 9, 2026, Sarepta Therapeutics, Inc.); the FDA FAERS public dashboard.
What does the label list?
From the label: adverse reactionsThe most common adverse reactions (incidence >20% and at least 5% higher than placebo) were upper respiratory tract infection, cough, pyrexia, headache, arthralgia, and oropharyngeal pain.
Table 1. Adverse Reactions Occurring in at Least 20% of Patients Treated with AMONDYS 45 and at a Rate at Least 5% More Frequently than in the Placebo Group in Study 1
| Adverse Reaction | AMONDYS 45 30 mg/kg Once Weekly (n = 57) % | Placebo (n = 31) % |
|---|---|---|
| Upper Respiratory Tract Infections | 65 | 55 |
| Cough | 33 | 26 |
| Pyrexia | 33 | 23 |
| Headache | 32 | 19 |
| Arthralgia | 21 | 10 |
| Oropharyngeal Pain | 21 | 7 |
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 described elsewhere in the labeling: Hypersensitivity reactions [see Warnings and Precautions ( 5.1 )] The most common adverse reactions (incidence >20% and at least 5% higher than placebo) were upper respiratory tract infection, cough, pyrexia, headache, arthralgia, and oropharyngeal pain. ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact Sarepta Therapeutics, Inc. at 1-888-SAREPTA (1-888-727-3782) 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 clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice. In the AMONDYS 45 clinical development program, 76 patients received at least one intravenous dose of AMONDYS 45 (30 mg/kg). All patients were male and had genetically confirmed Duchenne muscular dystrophy. Age at study entry was 7 to 20 years (mean 9.9 years). Most (88%) patients were White, and 9% were Asian. AMONDYS 45 was studied in a double-blind, placebo-controlled study (Study 1). …
Source: FDA drug label, Sarepta Therapeutics, Inc., effective January 9, 2026 (SPL set e9e5fd44-eeda-4580-bba1-a734828bbcc3), via openFDA; the full label on DailyMed
What do FAERS reports show?
851 reports list casimersen among the medicines taken, each a report of something that happened, not proof the medicine caused it; 10 are coded as a death and 119 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 21 reactions below, 5 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?
- Casimersen: 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