Sounds like 'ta-mox-e-fen'

Key points about tamoxifen

  • Tamoxifen is used to treat some types of breast cancer.
  • Tamoxifen is also called Genox.
  • Find out how to take it safely and possible side effects.
blue unaunahi tile generic

Tamoxifen is used to treat some types of breast cancer. Some breast cancers need the female hormone, oestrogen, to grow. Tamoxifen slows the growth of the cancer by blocking the effects of oestrogen in the breast.

Tamoxifen can be used both in women who have not yet gone through the menopause, and in women who have had menopause. It can also be taken by men who have breast cancer. It belongs to a group of medicines known as non-steroidal anti-oestrogens. Read more about breast cancer

In New Zealand, tamoxifen is available as tablets (10 mg and 20 mg).

  • The usual dose of tamoxifen is 20 mg once a day.
  • Tamoxifen is a long-term treatment; you may have to take it for several years.
  • Always take your tamoxifen exactly as your doctor has told you. The pharmacy label on your medicine will tell you how much to take, how often to take it, and any special instructions.

  • Timing: Take tamoxifen at the same time each day, either in the morning or the evening. You can take tamoxifen with or without food. If you have nausea (feeling sick), try taking tamoxifen with food or just before bed.
  • Missed dose: If you forget to take your dose, take it as soon as you remember. But, if it is nearly time for your next dose, just take the next dose at the right time. Do not take double the dose.
  • Keep taking tamoxifen regularly. Do not stop taking tamoxifen suddenly; speak to your doctor before stopping.

  • Do you have problems with your periods (menstruation)?
  • Have you had a stroke, deep vein thrombosis (DVT) or a blood clot in your lungs?
  • Are your pregnant or breastfeeding?
  • Are you taking any other medicines, including medicines you can buy without a prescription, such as herbal and complementary medicines?

If any of these apply, it’s important that you tell your doctor or pharmacist before you start tamoxifen. Sometimes a medicine isn’t suitable for a person with certain conditions, or it can only be used with extra care.

Like all medicines, tamoxifen can cause side effects, although not everyone gets them. Often side effects improve as your body gets used to the new medicine.

Hot flushes and sweats

This is quite common when you are taking tamoxifen. Hot flushes and sweats may improve after the first few months. You can try to reduce this effect by not smoking, reducing alcohol and avoiding hot drinks containing caffeine, such as tea and coffee. Try to dress in layers, so you can remove clothes as needed, and wear clothes made from natural fabrics, such as cotton. If hot flushes are troubling you, tell your doctor or nurse. There are some medicines that can help to reduce flushes.

Increased risk of blood clots

Taking tamoxifen increases your risk of getting blood clots in your leg (deep vein thrombosis or DVT) or your lung (called pulmonary embolism). Blood clots can be harmful. If you have any of the following symptoms, get medical attention immediately:

  • signs of blood clots in the leg such as pain, redness, heat and swelling of the calf, leg or thigh
  • signs of a blood clot in the lung such as shortness of breath, tightness in the chest or an unexplained cough or if you cough up blood.

Also, let your doctor know if:

  • you are planning a long-distance plane, car or train journey. Long periods of being inactive can increase your risk of developing blood clots. You may be advised to wear compression stockings (below-knee stockings that apply gentle pressure to help blood flow). These must be correctly fitted so get advice from a pharmacist or other healthcare professional.
  • you need to have surgery. This also increases your risk of getting blood clots. You may need to stop taking tamoxifen a few days before and after the surgery.

Other side effects

Side effects What should I do?
  • Nausea (feeling sick) or vomiting
  • Try taking tamoxifen with food or just before bed
  • Dizziness, headache 
  • These may go away with time
  • Feeling tired
  • Sleep problems 
  • Weight gain
  • These may go away with time
  • Tell your doctor if troublesome
  • Do not drive if you feel tired or dizzy
  • Heavy bleeding during your periods (heavier or more painful than usual), or unusual bleeding between your periods.
  • Tamoxifen can affect the lining of the womb 
  • Tell your doctor or call Healthline 0800 611 116 
Did you know that you can report a side effect to a medicine to CARM (Centre for Adverse Reactions Monitoring)? Report a side effect to a product(external link)

Tamoxifen may interact with a few medications and herbal supplements, so check with your doctor or pharmacist before starting tamoxifen or before starting any new medicines or supplements.

Medsafe Consumer Information Sheet
Genox(external link)
Tamoxifen Sandoz(external link)

  1. Tamoxifen(external link) New Zealand Formulary

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Credits: Sandra Ponen, Pharmacist. Healthify is brought to you by Health Navigator Charitable Trust.

Reviewed by: Angela Lambie, Pharmacist, Auckland

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