What the label lists and what reports show
Trastuzumab emtansine side effects
Trastuzumab emtansine's FDA label: “The most common adverse reactions (≥ 25%) with KADCYLA were fatigue, nausea, musculoskeletal pain, hemorrhage, thrombocytopenia, headache, increased transaminases, constipation and epistaxis.” FAERS holds 8,382 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 fatigue (757 reports).
- No generic listed
- Boxed warning
Check it at the source: the trastuzumab emtansine FDA label on DailyMed (effective April 1, 2026); the FDA FAERS public dashboard.
What does the label list?
From the label: adverse reactionsThe most common adverse reactions (≥ 25%) with KADCYLA were fatigue, nausea, musculoskeletal pain, hemorrhage, thrombocytopenia, headache, increased transaminases, constipation and epistaxis.
Table 3 Adverse Reactions Occurring in ≥ 10% of Patients on the KADCYLA Treatment Arm in the EMILIA Trial Grouped terms were used for the following Adverse Reactions: Thrombocytopenia: thrombocytopenia, platelet count…
| Reaction | All Grades (%) | Grade 3 – 4 (%) | All Grades (%) | Grade 3 – 4 (%) |
|---|---|---|---|---|
| Thrombocytopenia | 31 | 15 | 3.3 | 0.4 |
| Anemia | 14 | 4.1 | 11 | 2.5 |
| Nausea | 40 | 0.8 | 45 | 2.5 |
| Constipation | 27 | 0.4 | 11 | 0 |
| Diarrhea | 24 | 1.6 | 80 | 21 |
| Vomiting | 19 | 0.8 | 30 | 4.5 |
| Abdominal pain | 19 | 0.8 | 18 | 1.6 |
| Dry Mouth | 17 | 0 | 4.9 | 0.2 |
| Stomatitis | 14 | 0.2 | 33 | 2.5 |
| Fatigue | 36 | 2.5 | 28 | 3.5 |
| Pyrexia | 19 | 0.2 | 8 | 0.4 |
| Asthenia | 18 | 0.4 | 18 | 1.6 |
| Transaminases increased | 29 | 8.0 | 14 | 2.5 |
| Hypokalemia | 10 | 2.7 | 9 | 4.7 |
| Musculoskeletal pain | 36 | 1.8 | 31 | 1.4 |
| Arthralgia | 19 | 0.6 | 8 | 0 |
| Myalgia | 14 | 0.6 | 3.7 | 0 |
| Headache | 28 | 0.8 | 15 | 0.8 |
| Peripheral neuropathy | 21 | 2.2 | 14 | 0.2 |
| Dizziness | 10 | 0.4 | 11 | 0.2 |
| Insomnia | 12 | 0.4 | 9 | 0.2 |
| Epistaxis | 23 | 0.2 | 8 | 0 |
| Cough | 18 | 0.2 | 13 | 0.2 |
| Dyspnea | 12 | 0.8 | 8 | 0.4 |
| Rash | 12 | 0 | 28 | 1.8 |
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: Hepatotoxicity [See Warnings and Precautions (5.1) ] Left Ventricular Dysfunction [See Warnings and Precautions (5.2) ] Embryo-Fetal Toxicity [See Warnings and Precautions (5.3) ] Pulmonary Toxicity [See Warnings and Precautions (5.4) ] Infusion-Related Reactions, Hypersensitivity Reactions [See Warnings and Precautions (5.5) ] Hemorrhage [See Warnings and Precautions (5.6) ] Thrombocytopenia [See Warnings and Precautions (5.7) ] Neurotoxicity [See Warnings and Precautions (5.8) ] Metastatic Breast Cancer The most common adverse reactions (≥ 25%) with KADCYLA were fatigue, nausea, musculoskeletal pain, hemorrhage, thrombocytopenia, headache, increased transaminases, constipation and epistaxis. ( 6.1 ) Early Breast Cancer The most common adverse reactions (≥ 25%) with KADCYLA were fatigue, nausea, increased transaminases, musculoskeletal pain, hemorrhage, thrombocytopenia, headache, peripheral neuropathy, and arthralgia. To report SUSPECTED ADVERSE REACTIONS, contact Genentech at 1-888-835-2555 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. …
Source: FDA drug label, Genentech, Inc., effective April 1, 2026 (SPL set 23f3c1f4-0fc8-4804-a9e3-04cf25dd302e), via openFDA; the full label on DailyMed
What do FAERS reports show?
8,382 reports list trastuzumab emtansine among the medicines taken, each a report of something that happened, not proof the medicine caused it; 1,156 are coded as a death and 2,153 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, 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 emtansine: 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