Less common side effects


Different hormonal therapies have different side effects.

Find out more about:

Side effects of tamoxifen

Rare side effects of tamoxifen include an increased risk of:

  • blood clots
  • stroke
  • changes in vision.

Tamoxifen can also cause changes to the lining of the womb (uterus) and in rare cases has been associated with an increased risk of cancer of the uterus.

It’s important to see a doctor immediately if any new or unusual symptoms develop, in particular:

  • irregular vaginal bleeding
  • chest pain
  • warmth, pain, swelling or tenderness in an arm or leg.

Irregular vaginal bleeding doesn’t mean that a woman has cancer of the uterus but it’s important to be examined by a doctor to be sure.

It’s important to balance the risk of these rare side effects against the fact that anti-oestrogens lower the risk of breast cancer coming back and dying from breast cancer. Tamoxifen may have some other benefits in addition to treating breast cancer, including reducing the risk of osteoporosis and lowering cholesterol levels.

Side effects of aromatase inhibitors

Side effects of aromatase inhibitors include:

  • pain in bones or joints (arthralgia)
  • an increased risk of osteoporosis, which may increase the risk of bone fractures.

Doctors may measure a woman’s bone density before prescribing an aromatase inhibitor if she is at increased risk of osteoporosis. Calcium and vitamin D tablets may be recommended for women taking an aromatase inhibitor. Treatments are available that can improve bone strength.

A painkiller such as paracetamol can be helpful for women who experience pain in the bones or joints.

Long-term side effects of aromatase inhibitors are still being studied. For example, studies are investigating the effects of aromatase inhibitors on memory, concentration and heart disease.

Side effects of ovarian treatments

Surgery to remove the ovaries or radiotherapy to the ovaries causes permanent menopause. Women who have these treatments can no longer have children naturally.

Drugs that stop the ovaries from working also cause menopause, but this usually only lasts while taking the drugs. However, the effects of these drugs may be permanent if a woman is close to her natural menopause when she starts treatment.

Side effects of progestins

Treatment with progestins may increase a woman’s appetite, which means she might put on weight. Other possible side effects include muscle cramps and slight vaginal bleeding (spotting).