The most common side effects with Enhertu (which may affect more than 1 in 5 people) are nausea (feeling sick), tiredness, vomiting, alopecia (hair loss), constipation, decreased appetite, anaemia (low levels of red blood cells), neutropenia (low levels of neutrophils, a type of white blood cell that fights infection), diarrhoea, muscle and bone pain, increased levels of certain liver enzymes (transaminases), thrombocytopenia (low levels of blood platelets which can lead to bleeding and bruising) and leucopenia (low levels of white blood cells).

The most common serious side effects are neutropenia, anaemia, nausea, tiredness, leucopenia, lymphopenia, vomiting, thrombocytopenia, hypokalaemia (low blood potassium levels which can cause weakness, muscle cramps, tingling and heart rhythm disturbance), diarrhoea, pneumonia, neutropenia with fever, dyspnoea (difficulty breathing), decreased appetite, increased levels of certain liver enzymes, increased blood levels of the enzyme alkaline phosphatase, dyspnoea (difficulty breathing), weight loss, reduced ejection fraction (a measure of how well the heart pumps blood) and interstitial lung disease (disorders causing scarring in the lungs).

The frequency and seriousness of side effects that can occur with Enhertu depend on the type of cancer that is being treated.

For the full list of side effects and restrictions of Enhertu, see the package leaflet.