See also Warning section.

Before using trastuzumab emtansine, tell your doctor or pharmacist if you are allergic to it; or to any trastuzumab deruxtecan, trastuzumab emtansine, trastuzumab, or trastuzumab-hyaluronidase products; or if you have any other allergies. This product may contain inactive ingredients which can cause allergic reactions or other problems. Talk to your pharmacist for more details.

Before using this medication, tell your doctor or pharmacist your medical history, especially of: previous cancer treatments (including radiation therapy to the chest), current infection, heart disease, high blood pressure, lung problems, previous severe reaction to monoclonal antibody treatment, liver disease (including a rare liver condition called nodular regenerative hyperplasia).

Trastuzumab emtansine can make you more likely to get infections or may make current infections worse. Stay away from anyone who has an infection that may easily spread (such as chickenpox, COVID-19, measles, flu). Talk to your doctor if you have been exposed to an infection or for more details.

Tell your health care professional that you are using trastuzumab emtansine before having any immunizations/vaccinations. Avoid contact with people who have recently received live vaccines (such as flu vaccine inhaled through the nose).

To lower the chance of getting cut, bruised, or injured, use caution with sharp objects like razors and nail cutters, and avoid activities such as contact sports.

This drug may make you dizzy. Alcohol or marijuana (cannabis) can make you more dizzy. Do not drive, use machinery, or do anything that needs alertness until you can do it safely. Limit alcoholic beverages. Talk to your doctor if you are using marijuana (cannabis).

Before having surgery, tell your doctor or dentist about all the products you use (including prescription drugs, nonprescription drugs, and herbal products).

Older adults may be more sensitive to the side effects of this drug, especially heart problems (such as heart failure).

Tell your doctor if you are pregnant or plan to become pregnant. You should not become pregnant while using trastuzumab emtansine. Trastuzumab emtansine may harm an unborn baby. Your doctor should order a pregnancy test before you start this medication. Women using this medication should ask about reliable forms of birth control during treatment and for 7 months after the last dose. Men using this medication should ask about reliable forms of birth control during treatment and for 4 months after the last dose. If you or your partner becomes pregnant, talk to your doctor right away about the risks and benefits of this medication.

It is unknown if this drug passes into breast milk. Because of the possible risk to the infant, breastfeeding is not recommended while using this drug and for 7 months after the last dose. Consult your doctor before breastfeeding.