What the label lists and what reports show
Trastuzumab deruxtecan side effects
Trastuzumab deruxtecan's FDA label: “The most common adverse reactions (≥20%), including laboratory abnormalities, in patients with: HER2-Positive, HER2-Low, and HER2-Ultralow Breast Cancer, HER2-Mutant NSCLC, and HER2-Positive (including IHC 3+) […]” FAERS holds 10,021 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 nausea (1,219 reports).
- No generic listed
- Boxed warning
Check it at the source: the trastuzumab deruxtecan FDA label on DailyMed (effective May 15, 2026); the FDA FAERS public dashboard.
What does the patient leaflet say about side effects?
From the patient leaflet: What is the most important information I should know about ENHERTU?ENHERTU can cause serious side effects, including: Lung problems that may be severe, life-threatening or that may lead to death. If you develop lung problems your healthcare provider may treat you with corticosteroid medicines. Tell your healthcare provider right away if you get any of the following signs and symptoms: cough trouble breathing or shortness of breath fever other new or worsening breathing symptoms (such as chest tightness, wheezing) Low white blood cell count (neutropenia). Low white blood cell counts are common with ENHERTU and can sometimes be severe. Your healthcare provider will check your white blood cell counts before starting ENHERTU and before starting each dose. Tell your healthcare provider right away if you develop any signs or symptoms of an infection or have fever or chills during treatment with ENHERTU. Heart problems that may affect your heart's ability to pump blood. Your healthcare provider will check your heart function before starting treatment with ENHERTU and during treatment if needed. Tell your healthcare provider right away if you get any of the following signs and symptoms: new or worsening shortness of breath coughing feeling tired swelling of your ankles or legs irregular heartbeat sudden weight gain dizziness or feeling light-headed loss of consciousness Your healthcare provider will check you for these side effects during your treatment with ENHERTU. Your healthcare provider may reduce your dose, delay treatment or completely stop treatment with ENHERTU if you have severe side effects. Harm to your unborn baby. Tell your healthcare provider right away if you become pregnant or think you might be pregnant during treatment with ENHERTU. […]
Source: FDA drug label, Daiichi Sankyo Inc., effective May 15, 2026 (SPL set 7e67e73e-ddf4-4e4d-8b50-09d7514910b6), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsThe most common adverse reactions (≥20%), including laboratory abnormalities, in patients with: HER2-Positive, HER2-Low, and HER2-Ultralow Breast Cancer, HER2-Mutant NSCLC, and HER2-Positive (including IHC 3+) […]
Table 8: Common Adverse Reactions (≥10% All Grades or ≥2% Grades 3 or 4) in Patients Treated with ENHERTU in Combination with Pertuzumab in DESTINY-Breast09
| Reaction | All Grades % | Grade 3-4 % | All Grades % | Grades 3-4 % |
|---|---|---|---|---|
| Nausea | 75 | 5 | 34 | 0.3 |
| Diarrhea | 64 | 8 | 62 | 6 |
| Vomiting | 46 | 2.4 | 18 | 0.5 |
| Constipation | 33 | 0.3 | 12 | 0 |
| Abdominal pain Including abdominal discomfort, abdominal pain, abdominal pain lower,… | 23 | 0.3 | 13 | 0 |
| Stomatitis Including aphthous ulcer, mouth ulceration, oral mucosal eruption, and… | 16 | 1.3 | 17 | 1.3 |
| Dyspepsia | 12 | 0 | 6 | 0 |
| Fatigue Including asthenia, fatigue, lethargy, and malaise. | 53 | 8 | 42 | 2.1 |
| Pyrexia | 16 | 0 | 18 | 1.0 |
| Alopecia | 48 | 0 | 53 | 0.5 |
| Rash Including rash, rash macular, rash maculo-papular, rash pruritic, and rash pustular. | 17 | 0.3 | 22 | 0.3 |
| Pruritus | 11 | 0 | 11 | 0.3 |
| Upper respiratory tract infection Including Influenza, Influenza like illness,… | 33 | 1.6 | 30 | 0.5 |
| COVID-19 | 28 | 0.3 | 22 | 0.3 |
| Decreased appetite | 32 | 2.4 | 18 | 0.8 |
| Hypoalbuminemia | 11 | 0.3 | 8 | 0.3 |
| Decreased weight | 30 | 3.1 | 11 | 0.8 |
| Musculoskeletal pain Including back pain, bone pain, muscle spasms, musculoskeletal chest… | 24 | 1 | 33 | 0.3 |
| Headache Including headache and migraine. | 19 | 0.3 | 14 | 0 |
| Dysgeusia | 13 | 0 | 9 | 0 |
| Dizziness | 12 | 0.3 | 10 | 0 |
| Cough | 17 | 0.3 | 13 | 0 |
| Interstitial lung disease Interstitial lung disease includes chronic obstructive… | 12 | 0 | 1 | 0 |
| Dry eye | 11 | 0 | 6 | 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 significant adverse reactions are described elsewhere in the labeling: Interstitial Lung Disease/Pneumonitis [see Warnings and Precautions (5.1) ] Neutropenia [see Warnings and Precautions (5.2) ] Left Ventricular Dysfunction [see Warnings and Precautions (5.3) ] The most common adverse reactions (≥20%), including laboratory abnormalities, in patients with: HER2-Positive, HER2-Low, and HER2-Ultralow Breast Cancer, HER2-Mutant NSCLC, and HER2-Positive (including IHC 3+) Solid Tumors are decreased white blood cell count, nausea, decreased hemoglobin, decreased neutrophil count, decreased lymphocyte count, fatigue, decreased platelet count, increased aspartate aminotransferase, increased alanine aminotransferase, increased blood alkaline phosphatase, vomiting, alopecia, constipation, decreased blood potassium, decreased appetite, diarrhea, and musculoskeletal pain. ( 6.1 ) HER2-Positive Early Breast Cancer are decreased hemoglobin, increased alanine aminotransferase, increased aspartate aminotransferase, decreased white blood cell count, nausea, peripheral neuropathy, diarrhea, decreased neutrophil count, alopecia, fatigue, decreased lymphocyte count, rash, musculoskeletal pain, decreased blood potassium, constipation, vomiting, stomatitis, and decreased appetite.
Source: FDA drug label, Daiichi Sankyo Inc., effective May 15, 2026 (SPL set 7e67e73e-ddf4-4e4d-8b50-09d7514910b6), via openFDA; the full label on DailyMed
What do FAERS reports show?
10,021 reports list trastuzumab deruxtecan among the medicines taken, each a report of something that happened, not proof the medicine caused it; 2,575 are coded as a death and 2,439 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 2025 (2,248, against a median of 380 a year): FAERS counts follow reporting, which news, litigation and label changes can drive, not how often a reaction happens. Of the 19 reactions below, 16 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 deruxtecan: 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