Key points
- Tamoxifen is a tablet that blocks the female hormone oestrogen; it is used to treat hormone receptor-positive breast cancer (after surgery or in disease that has spread) and to lower the risk of cancer in high-risk women [1].
- About 5 years of tamoxifen roughly halved the chance of the cancer coming back in the first 4 years and cut deaths from breast cancer by about a third over 15 years [2].
- Continuing it to 10 years (instead of 5) lowered recurrences and deaths further [3].
- The most common side effects: hot flushes, vaginal discharge or bleeding, nausea and swelling [1].
- The drug label carries an important warning about womb cancer, stroke and blood clots in the lung; report any unusual vaginal bleeding to your doctor straight away [1].
What is this drug and how does it work?
For physicians
Tamoxifen is an "oestrogen agonist/antagonist" known by the brand names Nolvadex and Soltamox (the oral solution). It was first approved in the United States in 1977 [1].
The growth of many breast cancers depends on the hormone oestrogen. Tamoxifen competes with oestrogen for binding to the oestrogen receptor and so reduces the growth signal that oestrogen gives to breast cancer cells [1]. This is why the drug works only in cancers that have oestrogen receptors; in oestrogen receptor-negative breast cancer, tamoxifen has little effect on recurrence or death [2].
Unlike aromatase inhibitors, which are used only after the menopause, tamoxifen does not stop oestrogen production and is used in women before and after the menopause and in men with metastatic breast cancer [1]. Its oestrogen-like effect on the womb explains the increased risk of womb cancer [1].
Which cancers is it used for?
Your doctor may prescribe this drug for:
- Early oestrogen receptor-positive breast cancer [1, 2, 3]
- Oestrogen receptor-positive breast cancer that has spread [1]
- Ductal carcinoma in situ [1]
- Women at high risk of breast cancer [1, 4]
Whether it suits you depends on the type and stage of your cancer and your test results. Details of each use are in the section for doctors.
For physicians
| Cancer | Treatment setting | Key evidence |
|---|---|---|
| Early oestrogen receptor-positive breast cancer | Adjuvant treatment after surgery; also lowers the risk of cancer in the other breast [1] | EBCTCG meta-analysis of 20 trials: in ER-positive disease, about 5 years of tamoxifen reduced the recurrence rate ratio in years 0 to 4 to 0.53 and cut breast cancer deaths by about a third [2]. Continuing to 10 years in ATLAS reduced recurrence (617 vs 711 recurrences) [3]. |
| Oestrogen receptor-positive metastatic breast cancer | Treatment of advanced disease in women and men [1] | In premenopausal women, survival with tamoxifen was similar to ovarian removal or ovarian irradiation (HR for death 1.00); in men, an objective response of about 50% has been reported [1]. |
| Ductal carcinoma in situ (DCIS) | Lowers the risk of invasive cancer after surgery and radiotherapy [1] | NSABP B-24 trial: a 43% reduction in invasive breast cancer (44 vs 74 cases; RR 0.57) [1]. |
| Women at high risk of breast cancer | Lowers the incidence of breast cancer (chemoprevention) [1] | NSABP P-1 trial of 13,388 women: a 49% reduction in the risk of invasive breast cancer, especially oestrogen receptor-positive tumours [4]. |
The decision to use tamoxifen for prevention or DCIS should be made after discussing its benefits and serious risks with a doctor [1].
How it is taken and dose
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Treatment regimens and doses: index3 regimens
- Tamoxifen is taken as a tablet or an oral solution (Soltamox). Swallow the tablet whole with water or a non-alcoholic drink; you can take it with or without food. Taking it at the same time every day helps you remember [5].
- If you have been prescribed the oral solution, measure each dose only with the measuring cup supplied with the medicine [1].
- Your doctor decides how long treatment lasts; depending on its purpose it is usually several years. Never stop the medicine without talking to your doctor [1].
- If you forget a dose, take it as soon as you remember; but if it is nearly time for the next dose, skip the missed one. Never take two doses together [1].
- Before starting: exclude pregnancy in women of childbearing potential; baseline CBC and liver tests; assess any history of thromboembolism; with pre-existing hyperlipidaemia, triglycerides and cholesterol [1].
- Interactions: anastrozole or letrozole, strong CYP3A4 inducers, warfarin (contraindicated in DCIS and risk reduction) and strong CYP2D6 inhibitors; details in the section Interactions, pregnancy and precautions [1].
- Kidney and liver: the FDA label sets no renal or hepatic dose adjustment.
- Monitoring during treatment: periodic CBC (including platelets) and liver tests; periodic triglycerides and cholesterol with pre-existing hyperlipidaemia; an annual gynaecological examination and prompt investigation of any abnormal vaginal bleeding (routine endometrial sampling in asymptomatic women has shown no benefit); assessment of any visual disturbance (cataract, retinopathy); with bone metastases, hypercalcaemia in the first weeks (stop the drug in severe cases) [1].
For physicians
Standard doses (FDA label)
Adjuvant treatment of breast cancer
Early oestrogen receptor-positive breast cancer; lowering the risk of cancer in the other breastCycle length: Daily, continuously
Early oestrogen receptor-positive breast cancer; lowering the risk of cancer in the other breast
Before prescribing: Prescribing notes| Drug | Dose | Route | Schedule |
|---|---|---|---|
| Tamoxifen | 20 mg | Oral (tablet or solution; 10 mL of solution = 20 mg) | Once a day |
Doses above 20 mg a day give no additional clinical benefit [1].
Metastatic breast cancer
Oestrogen receptor-positive metastatic disease (adults)Cycle length: Daily, continuously
Oestrogen receptor-positive metastatic disease (adults)
Before prescribing: Prescribing notes| Drug | Dose | Route | Schedule |
|---|---|---|---|
| Tamoxifen | 20 to 40 mg a day | Oral (tablet or solution; 10 mL of solution = 20 mg) | Doses above 20 mg are divided into a morning and an evening dose |
[1]
DCIS and risk reduction in high-risk women
DCIS after surgery and radiotherapy; women at high risk of breast cancerCycle length: Daily, continuously
DCIS after surgery and radiotherapy; women at high risk of breast cancer
Before prescribing: Prescribing notes| Drug | Dose | Route | Schedule |
|---|---|---|---|
| Tamoxifen | 20 mg | Oral (tablet or solution; 10 mL of solution = 20 mg) | Once a day |
Contraindicated in these two uses: need for warfarin or a history of deep vein thrombosis or pulmonary embolism. Boxed warning for these uses: uterine malignancies, stroke and pulmonary embolism (some fatal) [1].
Doses follow the trial protocol, guideline or official drug label (source given in the notes of each regimen). Before prescribing, check blood counts, renal and hepatic function, drug interactions and the patient’s condition, and adjust the dose according to the drug label.
Side effects
The most common side effects:
- Hot flushes in most women [1].
- Vaginal discharge, irregular periods, nausea, swelling and skin changes [1].
- Mood changes, dizziness, headache, thinning hair and vaginal dryness [1].
- In cancer that has spread, bone or tumour pain sometimes gets worse for a while in the first weeks [1].
- In men: lower sex drive and erection problems [1].
For physicians
| Side effect | Tamoxifen | Placebo |
|---|---|---|
| Hot flushes | 64% | 48% |
| Fluid retention | 32% | 30% |
| Vaginal discharge | 30% | 15% |
| Nausea | 26% | 24% |
| Irregular periods | 25% | 19% |
| Weight loss of more than 5% | 23% | 18% |
| Skin changes | 19% | 15% |
Source: FDA label [1]. In the NSABP P-1 prevention trial, hot flushes were reported in 80% (vs 68% with placebo) and vaginal discharge in 55% (vs 35%) [1].
In metastatic breast cancer, bone or tumour pain and a temporary "flare" of the disease sometimes occur in the first weeks of treatment and usually settle quickly [1]. Other reported side effects include mood changes, depression, dizziness, headache, thinning hair and vaginal dryness [1]. In men, loss of libido and impotence have sometimes led to stopping the drug [1].
Serious side effects
These side effects are less common but serious; if you notice any sign of them, tell your team early:
- Womb cancer (uncommon but serious): report any unusual vaginal bleeding straight away, even after stopping the medicine [1].
- A blood clot: pain or swelling in one calf, or shortness of breath and sudden chest pain [1].
- Stroke: sudden weakness or numbness on one side of the body, or trouble speaking or seeing [1].
- Liver damage, cataracts and eye problems; regular liver tests and eye checks are needed [1].
- For most patients with breast cancer, the benefit of the medicine is far greater than these risks [1].
For physicians
Boxed warning: uterine malignancies, stroke and pulmonary embolism are serious and sometimes fatal adverse effects of tamoxifen. The incidence per 1000 woman-years in the P-1 trial (high-risk women) was: endometrial adenocarcinoma 2.20 vs 0.71 with placebo, uterine sarcoma 0.17 vs 0.04, stroke 1.43 vs 1.00 and pulmonary embolism 0.75 vs 0.25 [1]. In high-risk women and women with DCIS these risks should be discussed before starting; for most patients who have breast cancer, the benefit outweighs these risks [1].
- Uterus: any abnormal vaginal bleeding in a current or past user should be investigated promptly, and an annual gynaecological examination is recommended; routine endometrial sampling in asymptomatic women has shown no benefit [1].
- Blood clots: the risk of deep vein thrombosis and pulmonary embolism is increased, and higher when given with chemotherapy [1].
- Liver: changes in liver enzymes and, rarely, fatty liver, cholestasis, hepatitis, hepatic necrosis and liver cancer have been reported; periodic liver tests are needed [1].
- Blood: low platelets, low white cells or anaemia may occur; periodic blood counts are recommended [1].
- Eyes: cataracts and other eye problems (corneal changes, reduced colour perception, retinopathy) have been reported [1].
- Hypercalcaemia: may occur in the first few weeks in patients with bone metastases [1].
- Severe skin reactions (such as Stevens-Johnson syndrome) and hypersensitivity reactions including angioedema have been reported after marketing [1].
When should I call my doctor?
If you have any of these symptoms, contact your doctor straight away or go to an emergency department [1]:
- Abnormal vaginal bleeding, irregular periods, a change in vaginal discharge, or pain or pressure in the pelvis (even after stopping the medicine)
- Sudden chest pain, shortness of breath or coughing up blood
- Pain, tenderness or swelling in one or both calves
- Sudden weakness, numbness or tingling of the face, arm or leg, especially on one side of the body; sudden confusion, trouble speaking, sudden trouble seeing, loss of balance or a sudden severe headache
- Any change in your vision
- Swelling of the face, lips or tongue, or a severe skin reaction
Interactions, pregnancy and precautions
- Interaction with aromatase inhibitors: tamoxifen should not be taken with anastrozole or letrozole; the combination with anastrozole was no better than tamoxifen alone, and tamoxifen lowers the blood levels of these drugs [1].
- Warfarin: its anticoagulant effect may increase markedly; in breast cancer treatment, clotting tests should be monitored carefully, and in DCIS and preventive use, combined use is contraindicated [1].
- Some medicines (such as the antibiotic rifampicin) lower the amount of tamoxifen and should not be taken with it [1].
- Some antidepressants (such as paroxetine) may weaken tamoxifen; this is not yet clear. If you take an antidepressant, tell your doctor. Talk to your doctor before starting any antidepressant [1].
- Pregnancy: tamoxifen can harm an unborn baby. Use an effective non-hormonal method of contraception during treatment and for 2 months after the last dose (the pill, patch, implant or hormonal IUD are not suitable) [1]. Tamoxifen does not always cause infertility, even if your periods have become irregular [1].
- Breastfeeding: do not breastfeed during treatment and for 3 months after the last dose [1].
- Blood fats: in people with high blood fats, monitoring of triglycerides and cholesterol may be needed [1].
- Tamoxifen may make a T4 (thyroid) test result look high without a truly overactive thyroid [1].
Frequently asked questions
How many years should I take tamoxifen?
As adjuvant treatment after surgery, the drug label recommends 5 to 10 years [1]. In a large study, continuing the medicine to 10 years rather than stopping at 5 years further reduced recurrence and death from breast cancer, although the risk of womb cancer also rose slightly (about one more woman in every 100) [3]. Your doctor decides the right length based on your risk of recurrence.
Does tamoxifen cause womb cancer?
The risk of womb cancer rises with tamoxifen but is still low; each year about 2 in every 1000 women taking tamoxifen develop it [1]. Tell your doctor about any unusual bleeding from the womb. The most important steps are reporting any abnormal vaginal bleeding straight away and having an annual gynaecological examination [1].
Are hot flushes normal with tamoxifen?
Yes. Hot flushes are the most common side effect; about two in every 3 women have them [1]. If they are troublesome, talk to your doctor and do not stop the medicine on your own.
I have been through the menopause; why does my doctor suggest an aromatase inhibitor instead of tamoxifen?
In postmenopausal women with hormone receptor-positive breast cancer, a review of all the studies showed that 5 years of tablets such as letrozole or anastrozole, compared with 5 years of tamoxifen, slightly lowers deaths from breast cancer over 10 years and causes less womb cancer, but more bone fractures [6]. The choice between the two depends on your menopausal status, bone health and other conditions.
Is taking tamoxifen to prevent breast cancer right for me?
Tamoxifen is approved to lower risk in high-risk women, and in a large study it roughly halved the risk of breast cancer [4]. But because of the risk of blood clots, stroke and womb cancer, you should not take it for prevention if you have had a blood clot or need warfarin [1]. This decision should be made after a careful assessment of your risk.
Scientific evidence
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Key studies
3 itemsBreast Cancer, Version 4.2026, NCCN Clinical Practice Guidelines In Oncology
Pan-Asian adapted ESMO Clinical Practice Guidelines for the diagnosis, treatment and follow-up of patients with early breast cancer
Adjuvant Abemaciclib Plus Endocrine Therapy for Hormone Receptor-Positive, Human Epidermal Growth Factor Receptor 2-Negative, High-Risk Early Breast Cancer: Results From a Preplanned monarchE Overall Survival Interim Analysis, Including 5-Year Efficacy Outcomes
Related cancer types
References
6 referencesShow all references, 4 with a study cardClose the reference list
Numbers in the text, such as [1], refer to these sources. Sources with a “Study card” button are summarised in the site’s evidence library.
- 1
- 2
- 3
- 4
- 5Tamoxifen citrate tablets — Prescribing Information and Medication Guide
- 6Aromatase inhibitors versus tamoxifen in early breast cancer: patient-level meta-analysis of the randomised trials
This page is based on reputable scientific sources and was last updated on 28 October 2026. The content of this website is for educational and informational purposes only and does not replace consultation, diagnosis or treatment by a specialist physician. Consult your treating physician about any treatment decision.
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