> Western Medicines > Tamoxifen

What is Tamoxifen for?

Tamoxifen belongs to a class of medications called anti-oestrogen. It works by blocking the action of oestrogen hormone within the body. It is used to treat breast cancer and infertility in women caused by ovulation problems (the process of egg production and release). It is also used to prevent breast cancer in high risk individuals and to prevent gynaecomastia (abnormal enlargement of male breast) in men receiving long-term Bicalutamide treatment. Doctors may sometimes prescribe Tamoxifen for other conditions related to oestrogen levels in the body.

How to use it?

Tamoxifen is available as a tablet which is taken by mouth. You may take Tamoxifen with or without food.


Treatment of breast cancer
20 mg daily.


Prevention of breast cancer in women at high risk
20 mg daily for 5 years.


Anovulatory infertility
Initially 20 mg daily on days 2, 3, 4 and 5 of the menstrual cycle. If necessary, increase to 40 mg then 80 mg daily in subsequent menstrual cycles. If menstrual cycles are irregular, start the initial course on any day, with subsequent courses starting 45 days later, or on day 2 of the next cycle if menstruation occurs.


Gynaecomastia (antiandrogen-induced)
20 mg once weekly.

What are the side effects of Tamoxifen?

Common side effects of Tamoxifen include dizziness, tiredness, eyesight problems, headache, nausea, vomiting, diarrhoea, constipation, changes in taste, muscle or joint pain, hot flushes, and hair loss.

Who should not take Tamoxifen?

  • People allergic to Tamoxifen or any component of the formulation
  • Patients with a history of deep vein thrombosis or pulmonary embolism
  • Patients who are currently taking Anastrozole

Pharmacist Tips:

  • This medication can cause problems with your eyesight. Avoid driving or operating machinery until you know how you respond to Tamoxifen.
  • You will need regular blood tests, liver function tests, breast or eye examination during Tamoxifen treatment. Your doctor may order other tests too.
  • Avoid pregnancy during treatment and at least for 2 months after the final dose. If necessary, use an effective non-hormonal barrier method such as condoms.
  • Continue taking Tamoxifen even when you feel well.
  • Report to your doctor immediately if you experience menstrual irregularities, unusual vaginal bleeding or pelvic pain.

Common dosing schedule:

  • Tamoxifen is usually taken once daily. Try to take it at the same time each day.

This schedule is for reference only, adjustments may be made according to individual needs.


Some common medications Tamoxifen may interact with:

Tamoxifen may interact with many other medications. Please notify your doctor or pharmacist if you are taking the above medication, dosage adjustments might be needed.

Where to buy Tamoxifen in Hong Kong?

In Hong Kong, Tamoxifen is a prescription only medicine, and requires a prescription from a doctor to be purchased in a pharmacy. It can also be obtained from doctors. To find a pharmacy near you, refer to the list of pharmacies (“Authorized Sellers of Poisons”) from the Hong Kong Department of Health.


For more information about drug names and ingredients, you can visit Hong Kong’s Drug Office at https://www.drugoffice.gov.hk

Need more information?

For detailed information about the use of Tamoxifen in children, pregnancy and breastfeeding, and for questions about drug interactions, please check with your pharmacist or doctor.

Disclaimer: our goal is to provide you with the most relevant drug information and common dosage for Hong Kong. This information does not constitute medical advice. For specific treatment recommendations and advice, always discuss with your doctor or pharmacist, and follow the instructions included with your specific medicine.

Brands in Hong Kong
Available dosage
  • 10mg / 20mg (Tablets)
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