What the label lists and what reports show
Brincidofovir side effects
Brincidofovir's FDA label: “The most common adverse reactions (adverse events assessed as causally related by the investigator) experienced in the first 2 weeks of dosing with TEMBEXA were diarrhea and nausea.” FAERS holds 137 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 acute kidney injury (27 reports).
- No generic listed
- Boxed warning
Check it at the source: the brincidofovir FDA label on DailyMed (effective July 1, 2025, Emergent BioDefense Operations Lansing LLC); 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 TEMBEXA?TEMBEXA may cause serious side effects, including: • Liver problems. Your healthcare provider should perform blood tests to check your liver before you start taking TEMBEXA and during treatment with TEMBEXA for any signs or symptoms of liver problems. Call your healthcare provider right away if you have the following symptoms: o Stomach discomfort in the upper right side o Dark urine o Yellowing of your skin or the whites of your eyes (jaundice) • Diarrhea. Diarrhea is common in people who take TEMBEXA but can also be serious. Call your healthcare provider right away if you develop diarrhea with 4 or more stools per day over your usual daily number of stools. The most common side effects of TEMBEXA include: • Diarrhea • Nausea • Stomach pain • Vomiting TEMBEXA may cause low sperm counts and affect the ability to conceive children. […]
Source: FDA drug label, Emergent BioDefense Operations Lansing LLC, effective July 1, 2025 (SPL set 209aa94b-c613-4880-ad89-41be83d12c0a), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsThe most common adverse reactions (adverse events assessed as causally related by the investigator) experienced in the first 2 weeks of dosing with TEMBEXA were diarrhea and nausea.
Table 2: Adverse Reactions (All Grades) Reported in ≥2% of Subjects
| Adverse Reaction | TEMBEXA 200 mg N=392 % | Placebo N=208 % |
|---|---|---|
| Diarrhea a | 8 | 3 |
| Nausea | 5 | 1 |
| Vomiting b | 4 | 1 |
| Abdominal pain c | 3 | 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 clinically significant adverse reactions are described elsewhere in the labeling: • Elevations in hepatic transaminases and bilirubin [see Warnings and Precautions ( 5.2 )] • Diarrhea and other GI adverse events [see Warnings and Precautions ( 5.3 )] Common adverse reactions (occurring in at least 2% of TEMBEXA-treated subjects) were diarrhea, nausea, vomiting, and abdominal pain. ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact Emergent BioDefense Operations Lansing LLC at 1‑877-246-8472 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 safety of TEMBEXA has not been studied in patients with smallpox disease. The safety of TEMBEXA was evaluated in 392 adult subjects aged 18 to 77 years in Phase 2 and 3 randomized, placebo-controlled clinical trials. Of the subjects who received a 200 mg total weekly dose of TEMBEXA, 54% were male, 85% were White, 7% were Black/African American, 6% were Asian, and 10% were Hispanic or Latino. Twenty-one percent of subjects in the studies were age 65 or older. …
Source: FDA drug label, Emergent BioDefense Operations Lansing LLC, effective July 1, 2025 (SPL set 209aa94b-c613-4880-ad89-41be83d12c0a), via openFDA; the full label on DailyMed
What do FAERS reports show?
137 reports list brincidofovir among the medicines taken, each a report of something that happened, not proof the medicine caused it; 57 are coded as a death and 41 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, 1 is 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
Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms
What next?
- Brincidofovir: 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