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What the label lists and what reports show

Viltolarsen side effects

Viltolarsen's FDA label: “The most common adverse reactions (incidence ≥15% in patients treated with VILTEPSO) were upper respiratory tract infection, injection site reaction, cough, and pyrexia.” FAERS holds 165 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 pyrexia (20 reports).

  • No generic listed

Check it at the source: the viltolarsen FDA label on DailyMed (effective July 16, 2025, NS Pharma, Inc.); the FDA FAERS public dashboard.

What does the label list?

From the label: adverse reactions

The most common adverse reactions (incidence ≥15% in patients treated with VILTEPSO) were upper respiratory tract infection, injection site reaction, cough, and pyrexia.

Table 1: Adverse Reactions Reported in ≥10% of DMD Patients Treated with VILTEPSO 80 mg/kg Once Weekly (Pooled Studies 1 and 2)

Adverse Reaction* Upper respiratory tract infection includes the following terms: upper respiratory tract… ** Injection site reaction includes the following terms: injection site bruising,… VILTEPSO 80 mg/kg Once Weekly (n=16) %
Upper respiratory tract infection63
Injection site reaction25
Cough19
Pyrexia19
Contusion13
Arthralgia13
Diarrhea13
Vomiting13
Abdominal pain13
Ejection fraction decreased13
Urticaria13

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, continued

The most common adverse reactions (incidence ≥15% in patients treated with VILTEPSO) were upper respiratory tract infection, injection site reaction, cough, and pyrexia. ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact NS Pharma at 1-866 NSPHARM (1-866-677-4276) 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 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 clinical trials with VILTEPSO, 32 patients have been exposed to VILTEPSO once weekly, ranging between 40 mg/kg (0.5 times the recommended dosage) and 80 mg/kg (the recommended dosage), including 16 patients treated for greater than 12 months and 8 patients treated for greater than 24 months as part of an ongoing open-label extension study. All patients were male and had genetically confirmed DMD. Study 1 was a multicenter, 2-period, dose-finding study conducted in the United States and Canada in males 4 years to less than 10 years of age on a stable corticosteroid regimen for at least 3 months. During the initial period (first 4 weeks) of Study 1, patients were randomized (double-blind) to VILTEPSO or placebo. …

Source: FDA drug label, NDA212154 (Nippon Shinyaku), as published by NS Pharma, Inc., effective July 16, 2025 (SPL set 1ffff9a8-6d6a-4dcb-8493-1b6cc3a5d123), via openFDA; the full label on DailyMed

What do FAERS reports show?

165 reports list viltolarsen among the medicines taken, each a report of something that happened, not proof the medicine caused it; 7 are coded as a death and 40 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 22 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.

The 25 most reported reactions

  • Pyrexia (named in the label)20
  • Vomiting (named in the label)12
  • Illness11
  • Pneumonia8
  • Weight Increased8
  • Malaise7
  • Covid-196
  • Product Dose Omission Issue (a use or a product term, not a reaction)6
  • Cough (named in the label)5
  • Fall5
  • Off Label Use (a use or a product term, not a reaction)5
  • Sars-Cov-2 Test Positive5
  • Abdominal Discomfort4
  • Chest Pain4
  • Diarrhoea (named in the label)4
  • Influenza4
  • Nausea4
  • Upper Respiratory Tract Infection (named in the label)4
  • Adverse Event3
  • Anger3
  • Anxiety3
  • Blood Triglycerides Increased3
  • Catheter Site Infection3
  • Death (an outcome recorded in the report)3
  • Dyspnoea3

Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms

What next?

Viltolarsen: the full record
label, generics, price, shortages, recalls
Side effects hub
the most reported medicines and reactions