What does tamoxifen do?

Some breast cancers use oestrogen signals to receive growth instructions. Tamoxifen attaches to oestrogen receptors in breast tissue and interferes with that signal. It is an oral endocrine medicine, so it works throughout the body rather than only at the site of a tumour.

Doctors may use it after treatment for hormone-sensitive breast cancer, for certain advanced cancers, or to reduce the chance of breast cancer in selected people with increased risk. Its role depends on menopausal status, cancer features, previous treatment, and other medicines.

Take tamoxifen exactly as prescribed and keep a consistent routine. Do not stop it or double a missed dose without guidance. Tell the oncology team about antidepressants, blood thinners, supplements, pregnancy plans, and any new medicine because interactions can affect treatment.

Possible effects include hot flushes, night sweats, vaginal symptoms, mood changes, and menstrual changes. A clinician can suggest practical ways to manage them and decide whether another approach is appropriate. Read more about [Tamoxifen](/materials/tamoxifen/) and [Hormone Therapy for Cancer](/treatments/systemic-therapy/hormone-therapy-for-cancer/).

Contact your care team promptly for unusual vaginal bleeding, new pelvic pain, a breast change, or symptoms that are difficult to manage. Seek urgent medical help for sudden chest pain, breathlessness, coughing blood, or one-sided leg swelling and pain, which can signal a clot.

Ask why tamoxifen is recommended for your tumour or risk profile, how long the planned course is, which symptoms need review, and whether your current medicines interact with it. If prevention is the goal, ask about [Risk-Reducing Endocrine Therapy](/treatments/risk-reduction-and-prevention/risk-reducing-endocrine-therapy/).