What the label lists and what reports show
Emicizumab side effects
Emicizumab's FDA label: “Most common adverse reactions (incidence ≥ 10%) are injection site reactions, headache, and arthralgia.” FAERS holds 12,284 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 haemorrhage (4,539 reports).
- No generic listed
- Boxed warning
Check it at the source: the emicizumab FDA label on DailyMed (effective July 11, 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 HEMLIBRA?See " What is the most important information I should know about HEMLIBRA? " The most common side effects of HEMLIBRA include: redness, tenderness, warmth, or itching at the site of injection headache joint pain These are not all of the possible side effects of HEMLIBRA. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088. […] Get medical help right away if you have any of these signs or symptoms of blood clots during or after treatment with HEMLIBRA: swelling in arms or legs pain or redness in your arms or legs shortness of breath chest pain or tightness fast heart rate cough up blood feel faint headache numbness in your face eye pain or swelling trouble seeing If aPCC (FEIBA ® ) is needed, talk to your healthcare provider in case you feel you need more than 100 U/kg of aPCC (FEIBA ® ) total. Your body may make antibodies against HEMLIBRA, which may stop HEMLIBRA from working properly. Contact your healthcare provider immediately if you notice that HEMLIBRA has stopped working for you (e.g., increase in bleeds).
Source: FDA drug label, Genentech, Inc., effective July 11, 2025 (SPL set 2483adba-fab6-4d1b-96c5-c195577ed071), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsMost common adverse reactions (incidence ≥ 10%) are injection site reactions, headache, and arthralgia.
Table 2 Adverse Reactions Reported in ≥ 5% of Patients from Pooled Clinical Trials with HEMLIBRA
| Adverse Reaction | Number of Patients n (%) (N = 391) |
|---|---|
| Injection site reaction Includes injection site bruising, injection site discomfort,… | 85 (22%) |
| Headache | 57 (15%) |
| Diarrhea | 22 (6%) |
| Arthralgia | 59 (15%) |
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 serious adverse reactions are described elsewhere in the labeling: Thrombotic Microangiopathy Associated with HEMLIBRA and aPCC [see Warnings and Precautions (5.1) ] Thromboembolism Associated with HEMLIBRA and aPCC [see Warnings and Precautions (5.2) ] Most common adverse reactions (incidence ≥ 10%) are injection site reactions, headache, and arthralgia. ( 6.1 ) 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 following adverse reactions are based on pooled data from two randomized trials in adult and adolescent patients (HAVEN 1 and HAVEN 3), one single-arm trial in adult and adolescent patients (HAVEN 4), one single-arm trial in pediatric patients (HAVEN 2), and one dose-finding trial, in which a total of 391 male patients with hemophilia A received at least one dose of HEMLIBRA as routine prophylaxis. …
Source: FDA drug label, Genentech, Inc., effective July 11, 2025 (SPL set 2483adba-fab6-4d1b-96c5-c195577ed071), via openFDA; the full label on DailyMed
What do FAERS reports show?
12,284 reports list emicizumab among the medicines taken, each a report of something that happened, not proof the medicine caused it; 393 are coded as a death and 1,944 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. Reports rose sharply in 2024 (3,633, against a median of 527 a year): FAERS counts follow reporting, which news, litigation and label changes can drive, not how often a reaction happens. Of the 21 reactions below, 6 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?
- Emicizumab: 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