Tamoxifen

Pronunciation: ta-MOX-i-fen.

Generic name
tamoxifen
Drug class
Selective estrogen receptor modulator (SERM); antineoplastic agent
Form
Tablet (10 mg, 20 mg); oral solution also available in some markets (e.g. Soltamox in the US)
Route
Oral
Legal status
Prescription-only

Availability and supply rules vary by country

Trade names by country: United States · United Kingdom · Canada · Australia · New Zealand

Australia: Nolvadex / Nolvadex-D (AstraZeneca); Tamoxifen Sandoz and other generics (4) · Full directory

What tamoxifen is and how it works

Tamoxifen is a hormone-blocking medicine (a selective estrogen receptor modulator) used to treat hormone-receptor-positive breast cancer, and in some countries also to lower the risk of developing breast cancer in women who do not have it but are at high risk. It works by blocking the effect of estrogen on breast tissue. (1)

Tamoxifen's real, serious risks depend heavily on WHY it is being taken. When used to treat existing breast cancer, its benefits are considered to outweigh its risks. When used to reduce breast cancer risk in a woman who does not have cancer, or after treatment for DCIS, it carries a specific FDA boxed warning for uterine cancer, stroke, and blood clots in the lungs -- discuss this distinction, and what applies to your own situation, with your clinician.

Mechanism of action: how tamoxifen works

Tamoxifen is a selective estrogen receptor modulator (SERM) that competitively binds to estrogen receptors, producing tissue-selective effects: antagonist activity in breast tissue (the basis for its anticancer effect) but partial agonist activity in other tissues such as the endometrium (the basis for its endometrial-cancer risk) and bone. Its active metabolite, endoxifen, is formed via CYP2D6, which is why CYP2D6-inhibiting medicines can reduce its effectiveness. (2) (3)

What tamoxifen is used for

Treatment of breast cancer (adjuvant and metastatic)

Used to treat hormone-receptor-positive breast cancer, including adjuvant treatment after surgery and radiation for early-stage disease, and treatment of locally advanced or metastatic disease. Approved for this use in all markets reviewed. (1) (3) (5)

Risk reduction after DCIS (ductal carcinoma in situ)

Used after lumpectomy and radiation for DCIS to reduce the risk of invasive breast cancer developing later. This is one of the two settings covered by tamoxifen's FDA boxed warning. (1)

Breast cancer risk reduction in high-risk women without cancer

Used in the United States, United Kingdom, and Australia to reduce the risk of developing breast cancer in women assessed as being at high (or, in Australia, moderate-to-high) risk. This use is NOT approved in Canada, and the New Zealand product reviewed for this dossier does not list it either -- this is a genuine difference between markets, not an oversight. (1) (2) (4) (3)

Before taking tamoxifen

Do not take / not appropriate for

  • Do not take tamoxifen if you are pregnant, or could become pregnant without using effective, non-hormonal contraception -- tamoxifen must not be given during pregnancy, and women are advised to avoid pregnancy during treatment and for nine months after stopping. (all countries) (1) (3) (5)
  • Do not take tamoxifen if you have a known hypersensitivity to it or any ingredient in the tablet. (all countries) (1) (3)
  • If tamoxifen is being used for breast cancer risk-reduction (prevention) or after DCIS -- not for treating existing cancer -- do not take it if you have a history of blood clots in the legs or lungs (deep vein thrombosis or pulmonary embolism), a history of stroke, or you are taking a coumarin-type anticoagulant (such as warfarin). (United States, United Kingdom, Australia (where the prevention indication is approved)) (1) (2)
  • Do not take tamoxifen together with anastrozole. (United Kingdom) (2)

Tell your clinician about

  • Whether tamoxifen is being prescribed to treat existing breast cancer, or to reduce future risk -- the balance of risks and benefits, and the boxed-warning content that applies, differs between these uses.
  • Any personal or family history of blood clots, stroke, or endometrial (uterine) cancer.
  • Any abnormal vaginal bleeding, before starting and at any point during treatment.
  • Whether you are pregnant, could become pregnant, or are breastfeeding.
  • All other medicines, especially anticoagulants, other breast cancer medicines such as anastrozole, or medicines listed as CYP2D6 inhibitors (such as paroxetine, fluoxetine, or bupropion).
  • Any personal or family history of conditions affecting heart rhythm (QT prolongation) or low blood potassium/magnesium.
  • Any history of cataracts or other eye problems.
(1) (2) (3)

How to take tamoxifen

  • Taken by mouth, once daily or in divided doses, as directed by your prescriber.
  • Swallow tablets whole; do not stop taking tamoxifen or change your dose without talking to your clinician first, even if you feel well.
  • For early-stage breast cancer treatment and for risk-reduction/DCIS use, courses are typically planned for around 5 years -- your clinician will confirm the intended duration for your situation.
  • Attend all scheduled gynaecological check-ups and blood tests, and report any unusual vaginal bleeding promptly.
(1) (3)

Procedures and treatment changes

Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1) (2) (3) (4) (5)

Missed dose

If you miss a dose, take the next usual dose as soon as you remember. Do not take two doses at the same time to make up for a missed one.

Overdose

Seek urgent medical attention if you think too much tamoxifen has been taken. Reported overdose effects include hot flushes, nausea, vomiting, and vaginal bleeding; there is no specific antidote, and treatment is symptomatic. Contact your regional poison control centre for guidance in a suspected overdose. (3)

Side effects

Side effects and their urgency vary; report severe, persistent, or concerning symptoms.

Hot flushes and menopause-like symptoms.

What to notice: Hot flushes and menopause-like symptoms.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (3)

Vaginal discharge or bleeding, and changes to the menstrual cycle in premenopausal women.

What to notice: Vaginal discharge or bleeding, and changes to the menstrual cycle in premenopausal women.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (2) (5)

Nausea.

What to notice: Nausea.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (3)

Fluid retention.

What to notice: Fluid retention.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (3)

Serious warnings

Signs of uterine (endometrial) cancer or other endometrial changes — boxed_warning

Symptoms: Abnormal vaginal bleeding (including between periods, heavier-than-normal bleeding, or bleeding after menopause), changes in vaginal discharge, or new lower abdominal pain or pressure.

Action: Contact your clinician promptly for investigation -- this warning applies specifically to tamoxifen used for breast cancer risk-reduction (prevention) or after DCIS, per the FDA boxed warning and Health Canada's Serious Warnings and Precautions box, both based on real trial data showing increased uterine cancer risk in that setting. (1) (3) (5)

Signs of stroke — boxed_warning

Symptoms: Sudden weakness or numbness (especially on one side of the body), trouble speaking or understanding speech, sudden vision changes, or a sudden severe headache.

Action: Seek emergency medical help immediately. This risk is part of the FDA boxed warning for tamoxifen used in the breast cancer risk-reduction (prevention) or DCIS setting. (1) (3)

Signs of a blood clot in the lungs (pulmonary embolism) or legs (deep vein thrombosis) — boxed_warning

Symptoms: Sudden shortness of breath, chest pain that worsens with breathing, coughing up blood, or new swelling, pain, warmth, or redness in one leg.

Action: Seek emergency medical help immediately. This risk is part of the FDA boxed warning for tamoxifen used in the breast cancer risk-reduction (prevention) or DCIS setting, and is also flagged as a general thromboembolism risk (a two- to three-fold increase) across tamoxifen use more broadly. (1) (2)

Signs of vision changes (retinopathy or keratopathy) — high caution

Symptoms: Blurred vision lasting more than 2 weeks, or a change in colour vision.

Action: Report to your clinician for referral to an ophthalmologist. If tamoxifen is stopped promptly, vision usually returns to normal. (5)

Signs of a severe skin reaction — emergency

Symptoms: Widespread rash, blistering or peeling skin, or sores in the mouth, eyes, or genitals.

Action: Seek emergency medical help immediately and tell them you are taking tamoxifen -- Stevens-Johnson syndrome and toxic epidermal necrolysis have been reported, and a clinician will advise on stopping treatment. (2)

Interactions

  • Coumarin-type anticoagulants (such as warfarin) -- tamoxifen can significantly increase the anticoagulant effect; prothrombin time should be monitored closely. (1)
  • CYP2D6-inhibiting medicines (such as paroxetine, fluoxetine, and bupropion) can reduce the levels of tamoxifen's active form (endoxifen) and should be avoided where possible. (2)
  • Letrozole -- tamoxifen reduces letrozole plasma concentration. (1)
  • Rifampin and aminoglutethimide can reduce tamoxifen levels. (1)
  • Chemotherapy (cytotoxic agents) can further increase the risk of blood clots when combined with tamoxifen. (1) (5)
  • Anastrozole should not be combined with tamoxifen. (2)
  • Other medicines that prolong the QT interval can add to tamoxifen's own QT-prolonging effect. (2)

Pregnancy, breastfeeding, kidney/liver function, age

Pregnancy

Contraindicated. Tamoxifen must not be given during pregnancy; there have been reports of spontaneous abortion, birth defects, and fetal deaths in women who took it. Effective, non-hormonal contraception is advised during treatment and for nine months after stopping. (1) (2) (3) (4) (5)

Children

Not indicated for use in children; safety and effectiveness have not been established. (1) (2) (3) (4) (5)

Elderly

No specific dose adjustment based on age alone is described in the sources reviewed; candidates for treatment are often postmenopausal. (1) (2) (3) (4) (5)

Hepatic_impairment

Use with caution; discuss with your clinician if you have known liver problems. (1) (2) (3) (4) (5)

Renal_impairment

No specific dose adjustment is described in the sources reviewed for renal impairment alone. (1) (2) (3) (4) (5)

Source_ids

CA-HC-TEVA-TAMOXIFEN-PM-2026,US-DAILYMED-TAMOXIFEN-2026 (1) (2) (3) (4) (5)

Monitoring

Before starting

  • Confirmation of pregnancy status where relevant, and a discussion of contraception
  • Baseline gynaecological history and any history of blood clots, stroke, or endometrial cancer
  • Baseline eye examination if visual symptoms are a concern
  • ECG if there are risk factors for QT prolongation

During treatment

  • Routine gynaecological care, with prompt investigation of any abnormal vaginal bleeding.
  • Periodic blood counts, since low white cell or platelet counts have been reported.
  • Attention to any new visual symptoms.
  • ECG and electrolyte monitoring in patients with cardiac risk factors, given tamoxifen's QT-prolonging effect.
(2) (5)

Storage

Store tablets at room temperature in their original packaging, out of reach of children.

Professional information

Clinician-facing context only, sourced from the current US FDA prescribing information, UK SmPC, and Health Canada monograph for tamoxifen; verify against the current full label before prescribing.

United States / United Kingdom / Australia

Indication: Breast cancer treatment and risk-reduction/prevention

Dose summary: 20 mg daily for both treatment and risk-reduction/prevention use, typically for 5 years; doses above 20 mg given in divided doses for treatment.

Renal context: No specific renal dose adjustment described in the sources reviewed. (1) (2) (4)

Canada / New Zealand (product reviewed)

Indication: Breast cancer treatment only

Dose summary: 20-40 mg daily in a single or two divided doses; risk-reduction/prevention is explicitly not an approved indication in Canada, and not listed on the New Zealand product reviewed.

Renal context: No specific renal dose adjustment described in the sources reviewed. (3) (5)

Mechanism of action

Hepatic guidance

Use with caution in hepatic impairment; specific dose-adjustment data were not identified in the sources reviewed.

Overdose note

No specific antidote; overdose has been associated with QT-interval prolongation in the literature. Manage symptomatically; contact a poison control centre for guidance. (2) (3)

Frequently asked questions

Why does tamoxifen have a boxed warning if it's used to treat breast cancer?

The boxed warning is genuinely specific to certain uses, not all of them. It applies to tamoxifen used to reduce the risk of breast cancer in women who do not have cancer but are at high risk, and to reduce the risk of invasive cancer after treatment for DCIS. In those settings, a large clinical trial found more cases of uterine cancer, stroke, and blood clots in the lungs with tamoxifen than with placebo. The same FDA label states that when tamoxifen is used to treat existing breast cancer, its benefits outweigh these risks -- the warning is not saying tamoxifen is unsafe for cancer treatment. (1)

Is tamoxifen approved to prevent breast cancer everywhere?

No -- this genuinely differs by country. The United States, United Kingdom, and Australia have all approved tamoxifen for reducing breast cancer risk in high-risk women who do not have cancer. Canada has NOT approved this use: Health Canada's own current product monograph states directly that breast cancer prevention is not an approved indication in Canada, and tamoxifen is approved there for treatment only. The New Zealand product reviewed for this page also lists treatment only. (1) (2) (4) (3) (5)

What symptoms should I report immediately while taking tamoxifen?

Report any abnormal vaginal bleeding to your clinician promptly, and seek emergency care immediately for signs of stroke (sudden weakness, numbness, trouble speaking, sudden severe headache) or a blood clot in the lungs (sudden shortness of breath, chest pain, coughing up blood) or leg (new swelling, pain, warmth, or redness). (1) (3)

Is tamoxifen available in the US, UK, Europe, Canada, Australia, and New Zealand?

Yes, tamoxifen is authorised in all six markets reviewed, mostly as a generic medicine (its original Nolvadex brand has been discontinued in several markets). In the European Union, it is authorised nationally in individual member states rather than through one single centralised EU-wide approval, consistent with it being an old, off-patent medicine. (1) (2) (3) (4) (5)

What is the mechanism of action of tamoxifen?

Tamoxifen is a selective estrogen receptor modulator (SERM) that competitively binds to estrogen receptors, producing tissue-selective effects: antagonist activity in breast tissue (the basis for its anticancer effect) but partial agonist activity in other tissues such as the endometrium (the basis for its endometrial-cancer risk) and bone. Its active metabolite, endoxifen, is formed via CYP2D6, which is why CYP2D6-inhibiting medicines can reduce its effectiveness. (2) (3)

What is the generic name of Tamoxifen?

The generic name is tamoxifen. (1) (2) (3)

What class of drug is tamoxifen?

Tamoxifen is classed as: Selective estrogen receptor modulator (SERM); antineoplastic agent. (1) (2) (3)

References

  1. TAMOXIFEN CITRATE tablets, USP -- full prescribing informationU.S. Food and Drug Administration / DailyMed (NIH), full prescribing information, tamoxifen citrate tablets, USP · United States · accessed 2026-07-30 · source 1
  2. Tamoxifen 20mg Film-Coated Tablets -- Summary of Product Characteristicselectronic medicines compendium (emc), United Kingdom -- generic tamoxifen 20 mg film-coated tablets SmPC · United Kingdom · accessed 2026-07-30 · source 2
  3. TEVA-TAMOXIFEN (tamoxifen citrate tablets) Product Monograph Including Patient Medication InformationHealth Canada product monograph, Teva Canada Limited (TEVA-TAMOXIFEN) · Canada · accessed 2026-07-30 · source 3
  4. AusPAR: Tamoxifen (Nolvadex/Nolvadex-D) -- extension of indicationsTherapeutic Goods Administration (TGA), Australia -- AusPAR and Product Information for Nolvadex/Nolvadex-D (AstraZeneca) and generic tamoxifen products · Australia · accessed 2026-07-30 · source 4
  5. TAMOXIFEN SANDOZ (tamoxifen citrate) film-coated tablets -- New Zealand Data SheetMedsafe (New Zealand regulator) -- New Zealand Data Sheet for Tamoxifen Sandoz · New Zealand · accessed 2026-07-30 · source 5

Brand names by country

Single-ingredient tamoxifen names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.

Priority countries

United States

  • SOLTAMOX20 mg0mL · mayne pharma

United Kingdom

  • Tamoxifen (generic; Nolvadex/Nolvadex-D largely discontinued as a UK brand) (2)MHRA licensed emc smpc confirmed · 10 mg, 20 mg · Multiple generic manufacturers (e.g. Wockhardt UK, Tillomed, Viatris, Aurobindo)

Canada

  • NOLVADEX-D
  • APO-TAMOX

Australia

  • Nolvadex / Nolvadex-D (AstraZeneca); Tamoxifen Sandoz and other generics (4)TGA approved confirmed treatment and risk reduction · 10 mg, 20 mg · AstraZeneca Pty Ltd; Sandoz and other generic manufacturers

New Zealand

  • Tamoxifen Sandoz (5)Medsafe registered confirmed treatment only · 10 mg, 20 mg · Sandoz New Zealand
View brands in additional countries.

European Union

Tamoxifen (generic; nationally authorised product-by-product across EU member states) (2)

This page provides general reference information about tamoxifen and is not a substitute for advice from your prescriber. Tamoxifen's risks and benefits differ significantly depending on whether it is used to treat existing breast cancer or to reduce future risk -- discuss which applies to you, and all dosing and monitoring decisions, with the clinician managing your care.

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