What the label lists and what reports show
Fostamatinib side effects
Fostamatinib's FDA label: “The most common adverse reactions (≥5% and more than placebo) are diarrhea, hypertension, nausea, respiratory infection, dizziness, ALT/AST increased, rash, abdominal pain, fatigue, chest pain and neutropenia.” FAERS holds 7,695 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 (1,053 reports).
- No generic listed
Check it at the source: the fostamatinib FDA label on DailyMed (effective November 5, 2025, Rigel Pharmaceuticals, 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 TAVALISSE?See " What is the most important information I should know about TAVALISSE? " The most common side effects of TAVALISSE include: nausea dizziness respiratory infection rash tiredness chest pain stomach (abdomen) pain These are not all the side effects of TAVALISSE. For more information, ask your healthcare provider or pharmacist. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
Source: FDA drug label, Rigel Pharmaceuticals, Inc., effective November 5, 2025 (SPL set 21149cc3-049b-43e2-b141-c9499160556c), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsThe most common adverse reactions (≥5% and more than placebo) are diarrhea, hypertension, nausea, respiratory infection, dizziness, ALT/AST increased, rash, abdominal pain, fatigue, chest pain and neutropenia.
Table 3: Incidence of Common (≥ 5%) Adverse Reactions from Double-Blind Clinical Studies (FIT 1 and FIT 2)
| Reaction | Mild % | Moderate % | Severe % | TOTAL % | Mild % | Moderate % | Severe % | TOTAL % |
|---|---|---|---|---|---|---|---|---|
| Diarrhea Includes diarrhea and frequent bowel movement. | 21 | 10 | 1 | 31 | 13 | 2 | 0 | 15 |
| Hypertension Includes hypertension, blood pressure (BP) increased, BP diastolic abnormal,… | 17 | 9 | 2 | 28 | 10 | 0 | 2 | 13 |
| Nausea | 16 | 3 | 0 | 19 | 8 | 0 | 0 | 8 |
| Dizziness | 8 | 2 | 1 | 11 | 6 | 2 | 0 | 8 |
| ALT increased | 5 | 6 | 0 | 11 | 0 | 0 | 0 | 0 |
| AST increased | 5 | 4 | 0 | 9 | 0 | 0 | 0 | 0 |
| Respiratory infection Includes upper respiratory tract infection, respiratory tract… | 7 | 4 | 0 | 11 | 6 | 0 | 0 | 6 |
| Rash Includes rash, rash erythematous and rash macular. | 8 | 1 | 0 | 9 | 2 | 0 | 0 | 2 |
| Abdominal pain Includes abdominal pain, and abdominal pain upper. | 5 | 1 | 0 | 6 | 2 | 0 | 0 | 2 |
| Fatigue | 4 | 2 | 0 | 6 | 0 | 2 | 0 | 2 |
| Chest pain | 2 | 3 | 1 | 6 | 2 | 0 | 0 | 2 |
| Neutropenia Includes neutropenia and neutrophil count decreased. | 3 | 2 | 1 | 6 | 0 | 0 | 0 | 0 |
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 important adverse reactions, that can become serious are described elsewhere in the labeling: Hypertension [ see Warnings and Precautions (5.1) ] Hepatotoxicity [ see Warnings and Precautions (5.2) ] Diarrhea [ see Warnings and Precautions (5.3) ] Neutropenia [ see Warnings and Precautions (5.4) ] The most common adverse reactions (≥5% and more than placebo) are diarrhea, hypertension, nausea, respiratory infection, dizziness, ALT/AST increased, rash, abdominal pain, fatigue, chest pain and neutropenia. ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact Rigel Pharmaceuticals, Inc. at 1-800-983-1329 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. TAVALISSE was studied in two randomized, double-blind, placebo-controlled trials that were identical in design. The data described below reflect exposure to TAVALISSE in 102 patients with chronic ITP who had received one or more prior ITP treatment(s). Groups were stratified with respect to splenectomy and severity of thrombocytopenia. Patients randomized to the TAVALISSE arm received 100 mg orally twice daily. …
Source: FDA drug label, Rigel Pharmaceuticals, Inc., effective November 5, 2025 (SPL set 21149cc3-049b-43e2-b141-c9499160556c), via openFDA; the full label on DailyMed
What do FAERS reports show?
7,695 reports list fostamatinib among the medicines taken, each a report of something that happened, not proof the medicine caused it; 463 are coded as a death and 1,695 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 18 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?
- Fostamatinib: 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