Because people react to drugs in different ways, it is impossible to predict who is going to have side effects. Many women who take tamoxifen have no side effects at all while others will experience them. Some women find that one brand of tamoxifen causes more or less side effects than another, so if you experiencing side effects you may wish to ask your doctor if you can change to a different brand.
If side effects are severe, you may have to stop tasking the drug and a different hormonal drug may be prescribed. The commonest side effects, apart from nausea, are hot flushes and sweats, particularly at night.
Flushes and sweats; Sometimes the flushes will gradually lessen over the first few months but some women continue to have them for as long as they take tamoxifen. There are a number of self help strategies to help reduce or control hot flushes and sweats. For example, Some women find it helpful to avoid or cut down on tea, coffee, nicotine and alcohol. Evening primrose oil has been reported to be helpful in reducing sweats but it does not work for all women and it is very expensive. There are a lot of calories in Evening Primrose Oil so it may be fattening in some women. Some women have found complementary therapies have helped, and your GP may be able to give you details about obtaining these on the NHS. If you find your own therapist makes sure he or she is properly qualified and registered. If these measures do not work medical intervention may be appropriate:
An anti-depressant called venlaflexine has been used with some success but many women do not like the idea of taking an anti-depressant in the long term
Sometimes another drug called clonidine (Dixarit) can be prescribed to reduce hot flushes and sweats.
A small dose of a progesterone may be a very helpful in controlling this unpleasant side effect but this does increase the risks of blood clots and can increase the risk of weight gain and its affect of potential cancer cells is uncertain. See coping with weight gain.
If you are having very troublesome hot flushes do not hesitate to discuss alternative treatments with your doctor such as changing to an aromatase inhibitor (AI) if already on an AI trying a different brand such as arimidex, femara or aromasin.
Nausea and indigestion; Feelings of sickness (nausea) and indigestion are fairly common but can often be relieved by taking your tablet(s) with foods or milk or at night. Although mild nausea is quite common initially it usually wears off after a few weeks.
Weight gain; Weight gain can be a side effect of tamoxifen and this is sometimes due to water retention but at other times a consequence of a eating more either due to a increased appetite or mild nausea - "to settle the stomach" . See coping with weight gain.
Change in periods; Women who have not yet reached the menopause may notice their monthly periods change – they may become irregular, lighter or sometimes stop altogether. Some women also notice an increase in vaginal discharge and vulval itching.
Less common side effects include depression, tiredness and dizziness. Very rare side effect of tamoxifen includes:
Allergic reactions – this may include skin rashes
Temporary thinning of the hair
Headaches – some people affected by migraine have noticed a change in the pattern of their headaches
Thrombosis (blood clots) – pain, warmth, swelling or tenderness in an arm or leg or any chest pain must be reported to your doctor immediately
Visual problems – blurred or reduced vision is again very rare but any visual changes should be reported to your doctor
Rarely, women who are prescribed tamoxifen for advanced cancer, where there has been spread to the bones, may experience something called ‘tumour flare’ when they start taking Tamoxifen. This can cause a raised level of calcium in the blood (hypercalcaemia) with symptoms of nausea, vomiting and thirst. Often a short stay in hospital is necessary until the calcium levels have been reduced.
Tamoxifen can increase the effect of the drug warfarin, used to thin the blood in people prone to blood clots. If you are taking warfarin let your doctor know straight away.
What are the long term side effects of tamoxifen?
As tamoxifen is a relatively new drug the full long term effects of the drug are still being assessed through patient studies. In recent years there has been publicity about the long term effects of tamoxifen and its possible link with other types of cancer.
Tamoxifen studies have shown that women who take high doses of tamoxifen over a long period of time may have a slightly increased risk of developing cancer of the womb (endometrial cancer). This is very rare if the drug is taken for less than 5 years. However, this risk has to be weighted against the benefits of tamoxifen. If detected early, treatment for endometrial cancer is usually very successful.
Early warning signs are abnormal vaginal bleeding – although this is often caused by a non-cancerous condition such as a polyp. If taken for longer than 5 years, in some cancer centres women are given regular gynaecological check-ups to detect signs of endometrial cancer. An ultrasound scan, using sound waves, may be done to check for signs of endometrial cancer. An ultrasound scan, using sound waves, may be done to check for signs of change in the womb lining. A small probe is inserted into the vagina and the doctor can look at the scan on a screen. Any changes can be seen straight away. The scan is safe and only takes a few minutes.
Some studies on rats have shown a link between tamoxifen and liver cancer but this has not been proven in humans. There is little doubt that for most women the beneficial effects of tamoxifen far outweigh the risks.