What the label lists and what reports show
Baloxavir marboxil side effects
Baloxavir marboxil's FDA label: “Table 4 displays the most common adverse events (regardless of causality assessment) reported in at least 1% of adult and adolescent subjects who received XOFLUZA at the recommended dose in Trials T0821, T0831, and T0832.” FAERS holds 2,301 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 diarrhoea (136 reports).
- No generic listed
Check it at the source: the baloxavir marboxil FDA label on DailyMed (effective December 15, 2025, Genentech, Inc.); the FDA FAERS public dashboard.
What does the patient leaflet say about side effects?
From the patient leaflet: What are the possible side effects of XOFLUZA?XOFLUZA may cause serious side effects, including: Allergic reactions. Get emergency medical help right away if you develop any of these signs or symptoms of an allergic reaction: trouble breathing skin rash, hives or blisters swelling of your face, throat or mouth dizziness or lightheadedness The most common side effects of XOFLUZA for treatment of the flu in adults and adolescents (12 years of age and older) include: diarrhea bronchitis nausea sinusitis headache The most common side effects of XOFLUZA for treatment of the flu in children (5 years of age to less than 12 years of age) include: vomiting diarrhea XOFLUZA is not effective in treating or preventing infections other than influenza. Other kinds of infections can appear like flu or occur along with flu and may need different kinds of treatment. […]
Source: FDA drug label, Genentech, Inc., effective December 15, 2025 (SPL set e49e1a61-1b7c-4be5-ac84-af6240b511e7), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsTable 4 displays the most common adverse events (regardless of causality assessment) reported in at least 1% of adult and adolescent subjects who received XOFLUZA at the recommended dose in Trials T0821, T0831, and T0832.
Table 4 Incidence of Adverse Events Occurring in at Least 1% of Adult and Adolescent Subjects Receiving XOFLUZA in the Acute Uncomplicated Influenza Trials T0821, T0831, and T0832
| Adverse Event | XOFLUZA (N=1,440) | Placebo (N=1,136) |
|---|---|---|
| Diarrhea | 3% | 4% |
| Bronchitis | 3% | 4% |
| Nausea | 2% | 3% |
| Sinusitis | 2% | 3% |
| Headache | 1% | 1% |
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, continuedAdverse events reported in at least 1% of adult and adolescent influenza subjects treated with XOFLUZA included diarrhea (3%), bronchitis (3%), nausea (2%), sinusitis (2%), and headache (1%). ( 6.1 ) Adverse events reported in at least 5% of pediatric subjects (5 to < 12 years) treated with XOFLUZA included vomiting (5%) and diarrhea (5%). To report SUSPECTED ADVERSE REACTIONS, contact Genentech at 1-888-835-2555 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. The overall safety profile of XOFLUZA is based on data from 2,079 subjects, 5 years of age and older in 5 controlled clinical trials who received XOFLUZA. Of these subjects, 1,943 were adults and adolescents (≥ 12 years of age) and 136 were in the pediatric age group (5 to < 12 years of age) [see Clinical Studies (14) ]. …
Source: FDA drug label, Genentech, Inc., effective December 15, 2025 (SPL set e49e1a61-1b7c-4be5-ac84-af6240b511e7), via openFDA; the full label on DailyMed
What do FAERS reports show?
2,301 reports list baloxavir marboxil among the medicines taken, each a report of something that happened, not proof the medicine caused it; 136 are coded as a death and 449 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 19 reactions below, 9 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?
- Baloxavir marboxil: 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