What should you know about tamoxifen 40 mg?

Tamoxifen 40 mg is a higher prescribed strength that should be used only when your oncology clinician has selected it for your plan. Tamoxifen acts on oestrogen receptors, so it can be useful when breast cancer cells are hormone-sensitive or when endocrine treatment is being used for risk reduction. The strength on your label reflects an individual treatment decision, not a general target for everyone.

A clinician may choose a particular strength after considering the diagnosis, treatment goal, other medicines, and how your body responds. A larger number on the label does not mean the medicine is automatically more suitable or that a lower strength is ineffective. Never combine tablets or alter them to create a different dose unless the prescriber has given clear instructions. See [Tamoxifen](/materials/tamoxifen/) for medicine background and [Hormone Therapy for Cancer](/treatments/systemic-therapy/hormone-therapy-for-cancer/) for context.

Read the pharmacy label each time and take the prescribed amount at the instructed time. Keep the medicine away from children and do not share it. Tell your team about antidepressants, blood thinners, supplements, and any planned operation before making changes. Record missed doses and side effects so the clinician can decide whether the plan needs adjustment. Preventive use is discussed in [Risk-Reducing Endocrine Therapy](/treatments/risk-reduction-and-prevention/risk-reducing-endocrine-therapy/).

Seek emergency care for sudden breathing difficulty, chest pain, coughing blood, or a leg that becomes painful and swollen. Report unexpected vaginal bleeding, new pelvic pain, vision disturbance, intense headache, or jaundice promptly. Do not wait for a routine appointment if symptoms are severe, sudden, or worsening.

Ask why 40 mg was chosen, whether the tablets should be taken together, and what to do if one is missed. Clarify interaction checks, monitoring, expected side effects, and the safest way to contact the oncology team outside clinic hours.