What the label lists and what reports show
Trastuzumab side effects
Trastuzumab's FDA label: “Most common adverse reactions (≥ 5%) are headache, diarrhea, nausea, and chills.” FAERS holds 70,268 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 (6,872 reports).
- No generic listed
- Boxed warning
Check it at the source: the trastuzumab FDA label on DailyMed (effective May 29, 2026, Genentech, Inc.); the FDA FAERS public dashboard.
What does the label list?
From the label: adverse reactionsMost common adverse reactions (≥ 5%) are headache, diarrhea, nausea, and chills.
Table 3: Adverse Reactions (≥1%) in HERA (All Grades) The incidence of Grade 3 or higher adverse reactions was <1% in both arms for each listed term.
| Adverse Reactions | Herceptin (n = 1678) % | Observation (n = 1708) % |
|---|---|---|
| Headache | 10 | 3 |
| Paresthesia | 2 | 0.6 |
| Arthralgia | 8 | 6 |
| Back pain | 5 | 3 |
| Myalgia | 4 | 1 |
| Bone pain | 3 | 2 |
| Muscle spasm | 3 | 0.2 |
| Nasopharyngitis | 8 | 3 |
| Urinary tract infection | 3 | 0.8 |
| Diarrhea | 7 | 1 |
| Nausea | 6 | 1 |
| Vomiting | 3.5 | 0.6 |
| Constipation | 2 | 1 |
| Dyspepsia | 2 | 0.5 |
| Upper abdominal pain | 2 | 1 |
| Pyrexia | 6 | 0.4 |
| Peripheral edema | 5 | 2 |
| Chills | 5 | 0 |
| Asthenia | 4.5 | 2 |
| Influenza-like illness | 2 | 0.2 |
| Cough | 5 | 2 |
| Influenza | 4 | 0.5 |
| Dyspnea | 3 | 2 |
| URI | 3 | 1 |
| Rhinitis | 2 | 0.4 |
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 greater detail in other sections of the label: Cardiomyopathy [see Warnings and Precautions (5.1) ] Infusion Reactions [see Warnings and Precautions (5.2) ] Embryo-Fetal Toxicity [see Warnings and Precautions (5.3) ] Pulmonary Toxicity [see Warnings and Precautions (5.4) ] Exacerbation of Chemotherapy-Induced Neutropenia [see Warnings and Precautions (5.5) ] Adjuvant Breast Cancer Most common adverse reactions (≥ 5%) are headache, diarrhea, nausea, and chills. ( 6.1 ) Metastatic Breast Cancer Most common adverse reactions (≥ 10%) are fever, chills, headache, infection, congestive heart failure, insomnia, cough, and rash. ( 6.1 ) Metastatic Gastric Cancer Most common adverse reactions (≥ 10%) are neutropenia, diarrhea, fatigue, anemia, stomatitis, weight loss, upper respiratory tract infections, fever, thrombocytopenia, mucosal inflammation, nasopharyngitis, and dysgeusia. ( 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.
Source: FDA drug label, Genentech, Inc., effective May 29, 2026 (SPL set 492dbdb2-077e-4064-bff3-372d6af0a7a2), via openFDA; the full label on DailyMed
What do FAERS reports show?
70,268 reports list trastuzumab among the medicines taken, each a report of something that happened, not proof the medicine caused it; 8,319 are coded as a death and 20,178 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 22 reactions below, 13 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?
- Trastuzumab: 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