Sounds like 'ta-mox-e-fen'

Easy-to-read medicine information about tamoxifen – what it is, how to take tamoxifen safely and possible side effects.

Type of medicine Also called
  • Belongs to a group of medicines known as non-steroidal anti-oestrogen (use treat some types of breast cancer)
  • Genox
  • Tamoxifen Sandoz

What is tamoxifen?

  • Tamoxifen is used to treat some types of breast cancer.
  • Some breast cancers need the female hormone, oestrogen, to grow. Tamoxifen works by blocking the effects of oestrogen in the breast, and stops the cancer cells from growing.  
  • It belongs to a group of medicines known as non-steroidal anti-oestrogens.
  • Read more about breast cancer


  • The usual dose of tamoxifen is 1 tablet (20 mg) once a day.
  • Treatment with tamoxifen is usually continued for 5 years.

How to take tamoxifen

  • Take tamoxifen at the same time each day.
  • You can take tamoxifen with or without food.
  • If you have nausea (feeling sick), try taking tamoxifen with food or just before bed.
  • It is not harmful if you miss a dose of tamoxifen. If you forget to take your tablet, take it as soon as you remember that day.
  • But, if it is nearly time for your next tablet, just take the next tablet at the right time. Do not take double the amount of tablets.
  • Do not stop taking tamoxifen suddenly; speak to your doctor before stopping.

Some possible side effects

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.

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 
  • Hot flushes
  • Vaginal bleeding or discharge
  • Weight gain
  • These may go away with time.
  • Tell your doctor if troublesome.
  • Allergic reaction such as skin rash, itching, swelling of the lips, face, and mouth or difficulty breathing
  • Heavy bleeding during your periods (heavier than usual), or unusual bleeding between your periods.
  • Pain or swelling in your lower leg, or any sudden breathing problems 
  • Tell your doctor immediately or ring HealthLine.


Tamoxifen may interact with a few medications and herbal supplements, so check with your doctor or pharmacist.

Learn More

Medsafe Consumer Information Sheet
Tamoxifen Sandoz

Credits: Sandra Ponen, Pharmacist. Reviewed By: Dr Janine Bycroft, GP, Health Navigator NZ