What the label lists and what reports show
Entecavir side effects
Entecavir's FDA label: “In adults, the most common adverse reactions (≥3%, all severity grades) are headache, fatigue, dizziness, and nausea.” FAERS holds 11,608 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 drug resistance (403 reports).
- Generic listed
- Boxed warning
Check it at the source: the entecavir FDA label on DailyMed (effective November 6, 2019, E.R. Squibb & Sons, L.L.C.); 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 BARACLUDE?BARACLUDE may cause serious side effects. See “What is the most important information I should know about BARACLUDE?” The most common side effects of BARACLUDE include: • headache • tiredness • dizziness • nausea Tell your healthcare provider if you have any side effect that bothers you or that does not go away. These are not all the possible side effects of BARACLUDE. For more information, ask your healthcare provider or pharmacist. Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.
Source: FDA drug label, E.R. Squibb & Sons, L.L.C., effective November 6, 2019 (SPL set 046e61c9-9298-4b2e-b76e-b26b81fecd20), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsIn adults, the most common adverse reactions (≥3%, all severity grades) are headache, fatigue, dizziness, and nausea.
Table 3: Clinical Adverse Reactions a of Moderate-Severe Intensity (Grades 2‑4) Reported in Four Entecavir Clinical Trials Through 2 Years
| Body System/ Adverse Reaction | BARACLUDE 0.5 mg n=679 | Lamivudine 100 mg n=668 | BARACLUDE 1 mg n=183 | Lamivudine 100 mg n=190 |
|---|---|---|---|---|
| Any Grade 2–4 adverse reaction a | 15% | 18% | 22% | 23% |
| Diarrhea | <1% | 0 | 1% | 0 |
| Dyspepsia | <1% | <1% | 1% | 0 |
| Nausea | <1% | <1% | <1% | 2% |
| Vomiting | <1% | <1% | <1% | 0 |
| Fatigue | 1% | 1% | 3% | 3% |
| Headache | 2% | 2% | 4% | 1% |
| Dizziness | <1% | <1% | 0 | 1% |
| Somnolence | <1% | <1% | 0 | 0 |
| Insomnia | <1% | <1% | 0 | <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, continuedThe following adverse reactions are discussed in other sections of the labeling: • Exacerbations of hepatitis after discontinuation of treatment [see Boxed Warning, Warnings and Precautions (5.1) ]. • Lactic acidosis and severe hepatomegaly with steatosis [see Boxed Warning, Warnings and Precautions (5.3) ]. • In adults, the most common adverse reactions (≥3%, all severity grades) are headache, fatigue, dizziness, and nausea. The adverse reactions observed in pediatric patients were consistent with those observed in adults. (6.1) To report SUSPECTED ADVERSE REACTIONS, contact Bristol-Myers Squibb at 1-800-721-5072 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. 6.1 Clinical Trial 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. Clinical Trial Experience in Adults Compensated Liver Disease Assessment of adverse reactions is based on four studies (AI463014, AI463022, AI463026, and AI463027) in which 1720 subjects with chronic hepatitis B virus infection and compensated liver disease received double-blind treatment with BARACLUDE 0.5 mg/day (n=679), BARACLUDE 1 mg/day (n=183), or lamivudine (n=858) for up to 2 years.
Source: FDA drug label, E.R. Squibb & Sons, L.L.C., effective November 6, 2019 (SPL set 046e61c9-9298-4b2e-b76e-b26b81fecd20), via openFDA; the full label on DailyMed
What do FAERS reports show?
11,608 reports list entecavir among the medicines taken, each a report of something that happened, not proof the medicine caused it; 1,880 are coded as a death and 4,431 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, 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?
- Entecavir: 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