Understanding side effects experienced by women prescribed hormone therapy (SWITCH)

Thousands of women with breast cancer are prescribed hormone therapy, but many stop taking it because of side effects—and the specific brand they receive may be making things worse. This study addresses a gap in knowledge: whether switching between different brands of the same hormone therapy affects how well patients tolerate the drug and whether they stick with treatment. Currently, patients may be given different brands at different times due to pharmacy stock or prescribing changes, but no one has systematically tracked whether these switches cause new or worsening side effects. The research will follow a nationwide cohort of breast cancer patients over nine months, collecting self-reported side effects, adherence levels, and any brand changes. In-depth interviews with a subset of patients will explore their personal experiences. If this research succeeds, it could change how hormone therapies are prescribed and dispensed. The NHS and other healthcare systems might standardise brand continuity, or flag patients at risk of side effects from a switch. This would directly improve quality of life for breast cancer patients and reduce the number who abandon a life-saving treatment due to avoidable discomfort. It could also inform pharmacy supply chains and procurement policies, ensuring that brand changes are minimised or managed more carefully.