Tamoxifen (Oral)

Tamoxifen is regularly prescribed as part of the drug therapy used to treat and prevent hormone-receptor-positive breast cancer in both men and women, It works to reduce the risk of returning or new cancers by as much as 50%.


Tamoxifen (also sold as Nolvadex) was approved and licensed by the U.S. Food and Drug Administration (FDA) in 1998, and has become a useful tool in the treatment of hormone-receptor-positive breast cancer. Tamoxifen won't work on hormone-receptor-negative breast cancer.

It works by blocking the actions of the female hormone estrogen. This is clinically useful as some types of aggressive breast cancers rely on this hormone for growth. Since its approval the versatile drug has been used in the successful treatment of millions of women and men.

Because Its action has a hormonal basis (which also explains why it only works on certain types of breast cancer) it is often the first hormonal therapy medicine choice for postmenopausal women, as well as premenopausal women. It is regularly prescribed for women with a diagnosis and treatment plan for ductal carcinoma in situ (DCIS) that is hormone receptor-positive.

Tamoxifen is also useful in cases where women with women with hormone-positive breast cancer are found to have tumours that have spread to other parts of the body. In these cases there is clinical evidence that using tamoxifen can often help slow or stop the growth of the cancer, and might even shrink some tumors. This is one of the reasons for its regular prescription on a long-term basis to large number of women..

There are a number of additional reasons why Tamoxifen can be a good choice in the treatment of breast cancer. It has a number of health benefits for regular users, or those which take the medication over a long-term period. For example, it activates estrogen's ability to positively affect bone and liver cells. In this particular case, this means it can help protect women's bones and cut their bone loss after the menopause.

For early- stage breast cancer, this drug is mainly used for women who have not yet gone through menopause. (If you have gone through menopause, aromatase inhibitors are usually used instead.) It can also be a good choice for postmenopausal women who struggle with other medications that work as an aromatase inhibitor.

Condition(s) treated

  • Breast cancer

Type of medicine

  • Selective estrogen receptor modulators (SERMs)

Side Effects

There are a wide range of side effects to be considered when taking this medication although many people take it regularly without any negative impacts. However, it is very important to be aware of possible side effects and report significant ill-effects to your physician to see if there are better options for you. Some of these side effects can be very serious.

An increased risk of other kinds of cancer is an important factor for both you and your prescribing physician to consider. Evidence from clinical trials has shown Tamoxifen increases the chance of cancer of the uterus (womb) in some women taking it.

We also know that tamoxifen may cause cancer or other problems of the uterus (womb) in women. It also causes liver cancer in rats. In addition, tamoxifen has been reported to cause cataracts and other eye problems. Discuss these possible effects with your doctor. Finally, among the highly serious side effects - Tamoxifen may cause blockages to form in a vein, lung, or brain.

People taking Tamoxifen have also reported they have suffered hot flushes, nausea, cramps in their legs, aching muscles, hair thinning, headaches, and a numb or tingling feeling in the skin. Some men have aksi reported that they have lost either their sexual interest or ability while taking this drug.

These are more low-risk side effects and, while they should be reported, they are not thought to create serious cause for concern. There are a number of other serious symptoms that should be reported with urgency. These include changes in the your vision (for example, if it becomes blurry), any pain around the eye, if you feel you are suddenly easy to bruise or notice changes in the way you bleed.

Other points of concern include mental or mood changes, swelling or accumulation of fluid around your ankles or feet. Finally, unusual tiredness should also be reported and investigated.

The side effects at the most serious end of the scale are any stomach or abdominal pain, ongoing and persistent nausea or vomiting, if you notice that your urine is very dark, or sins of problems with your liver such as yellowing eyes or a look of yellow on your skin. You should also remain vigilant for other signs of infection, such as a fever or persistent sore throat).

The most commonly reported side effects of this drug are that women may find they have missed, or irregular periods and the amount of urine they produce can fall. People may also report a feeling of warmth, noisy breathing, redness of the upper body, skin changes, swelling, weight gain or loss and a white or brownish unusual vaginal discharge.

The list of possible side effects extends even further to the less common examples of

stomach cramps, black stools, bleeding gums, bone pain, feeling down. hair loss, headaches, irritability, genital itching and mild nausea or vomiting. The last points mentioned here are skin rashes, pelvic discomfort, trouble concentrating or sleeping and unusual bleeding.

As with all medication there is also the possibility of a serious allergic reaction to the active ingredients. The signs of this would include a developing rash, any itching or swelling of parts of the body - in particular around the face or tongue and episodes of, severe dizziness. In the most serious cases the person may also have trouble breathing. All of these situations require immediate medical attention.


The exact dose of tamoxifen that's needed to be prescribed will depend on the condition being treated. It may take several months of drug therapy for the effect of the medication to be apparent and your dosage may need ot be adjusted duing this period to be as effective as possible.

The usual adult dose given to people with a diagnosis of metastatic breast is

20 to 40 mg orally. If the prescription is for more than 20 mg in total then this should be split into divided to doses to be taken throughout the day (often morning and evening.)

If that patient has a diagnosis of DCIS, then Tamoxifen is usually prescribed at 20 mg orally daily for the five years that follow the patient's breast surgery and radiation treatment. The preferred dose is also 20 mg orally daily for five years if the treatment need is to reduce the incidence of breast cancer in women at high risk.

If tamoxifen is being administered as treatment of node-positive breast cancer in postmenopausal women after mastectomy, axillary dissection, and breast irradiation then the usual adult dose is 10 mg orally two to three times a day for five years.

If the patient has received a terminal diagnosis than tamoxifen may be given as part of palliative treatment to improve quality of life but not treat the condition. In these cases the usual adult dose will be from 10 to 20 mg orally twice a day.

Despite some contraindications, there are some situations where tamoxifen may be administered to children. These include McCune-Albright Syndrome and precocious puberty. in these cases girls aged two to ten years old with McCune-Albright Syndrome could take 20 mg of tamoxifen once a day. This should be continued for up to a year.

If this medication is being administered in the treatment of precocious puberty then the dose is the same.

It is important that Tamoxifen is taken regularly in order to get the most benefit. This means you must take care to get your prescription refilled before you run out.


Tamoxifen should not be taken alongside the groups of drugs which work by inhibiting the action of the enzyme CYP2D6. That's because these medications interfere with the way this drug is broken down by the body and metabolised. The concern is that, in combination, these drugs mean lower blood levels of the active ingredient in Tamoxifen.

In particular, anyone taking Tamoxifen should avoid:

  • antidepressants that act as selective serotonin reuptake inhibitors (SSRIs) or selective
  • noradrenergic reuptake inhibitors (SNRIs)¬†- paroxetine, fluoxetine, bupropion, and duloxetine
  • antipsychotics¬†- thioridazine, perphenazine, and pimozide
  • cardiac drugs - quinidine and ticlopidine
  • medications for infectious disease¬†- terbinafine and quinidine
  • cinacalcet.

It's also important that you talk to your doctor before using tamoxifen alongside soy products. That's because there is a suggestion that soy can trigger the growth of breast cancer tumours and undermine the health-promoting impacts of Tamoxifen.


There are a wide range of issues to consider and discuss with your prescribing health professional before taking tamoxifen. Your doctor or pharmacist needs to know if you already know you are allergic to this treatment, or any other allergies you already know you have. These could be triggered by inactive ingredients in tamoxifen so you need to provide as much information as possible for your own health.

There are also a number of pre-existing health conditions which would indicate that tamoxifen is not suited to you. If you are taking the drug to try and cut your risk of breast cancer, or if your cancer diagnosis is limited to the milk ducts, then you need to be particularly careful.

The risks here are where you have a history of blood clots (such as, deep vein thrombosis, pulmonary embolism or stroke). Any condition which requires treatment with a "blood thinner" (such as warfarin) should also be carefully discussed. In some cases it may mean this is not the best drug for you.

Some of the clinical research into the action of Tamoxifen found there was a clear risk of strokes, pulmonary emboli, and uterine malignancies, some of which served to be fatal. This means it is important to discuss the potential benefits versus the potential risks of this drug with your prescribing physician before you start taking it. Generally, the many benefits of taking Tamoxifen will outweigh the risks of further harm to women that already have a breast cancer diagnosis.

There are several other conditions associated with risks when taking this drug. You need to talk to your physician about whether Tamoxifen is right for you if you know you have have high cholesterol or triglycerides, or you have a limited or no ability to walk (making you immobilie). Other conditions or social factors like diabetes, high blood pressure, smoking, cataracts, or liver disease may also have an impact on how this drug works for you. This means it's important to have a full and frank conversation with your doctor about your needs and lifestyle.

It's also important to explain to your doctor or pharmacist if you are taking any additional treatments, even if these are herbal by nature. Your health professional needs full details of any products you are using, either prescription drugs or nonprescription drugs, before you agree to be scheduled for surgery. This is because these products can interact with the active ingredients in Tamoxifen and have unexpected and unwanted effects.

The other warnings around tamoxifen are that it is not recommended for use during pregnancy as there is a risk of harm to the unborn child. As such, it's important to ensure a woman has a negative pregnancy test, or is having their period, when they first start their drug treatment. Patients of childbearing age should also understand they must use a non-hormone, reliable form of contraception during their treatment, and for two months after.

There is no evidence at the current time about whether this medication passes into breast milk because this research could create a risk for infants. This means that breastfeeding is not recommended while using this drug as the possible effects have not been explored. Consult your doctor if you are committed to breastfeeding during your treatment to see if other formulations may be more suitable.

Because Tamoxifen has a blood-thinning effect you may need to stop using this medicine if you need surgery or medical tests or if you will be on bed rest.. Any doctor or surgeon who treats you should know that you are taking tamoxifen.


As with all prescribed and non-prescribed medications, tamoxifen should be kept in a cool, dry environment away from children in a tightly sealed container. It should be kept in its original box and packaging, away from excessive heat and moisture.

If you are left with excess amounts of tamoxifen then it should not be disposed of by flushing down the toilet. Instead, this medication requires special disposal to ensure that pets, children, and other people cannot consume them. It can be useful to talk to your pharmacist to find out if there are medicines take-back programs operating near you.


Tamoxifen is a popular and useful oestrogen-inhibitor which is often prescribed in the treatment of breast cancers. Its prescription is most clinically appropriate for cases where patients, either male or female, have been diagnosed with hormone-receptor-positive breast cancer which is still in the early stages but they have already had surgery (or nuclear treatments, such as chemotherapy and radiation). In these cases, it can be used to reduce the risk of the cancer coming back in the future. It is also used in more established cases where the patient is considered to have an advanced-stage disease and there is a need to manage their symptoms.

Tamoxifen also has other uses, It can be prescribed to help reduce the risk of breast cancer for persons that haven't been diagnosed with breast cancer but have a high risk of developing the disease, perhaps due to genetic or other risk factors.

The benefits of the drug for many people are that it can:

Reduce the chance of breast cancer returning in postmenopausal women by as much as 50% (from as high as 40%) and by 30% to 50% where the patient is a premenopausal woman.

  • Cut the risk of developing a new cancer in the patient's other breast by as much as 50%.
  • Help to shrink these types of breast cancer in the run-up to surgery in the hope that such surgery may be more effective. Tamoxifen can be used after surgery for as long as five to ten years and is believed to cut the chances of the condition returning.

Help to slow incidences of advanced (metastatic) hormone-receptor-positive breast cancer in women, regardless of their menopausal status.

However, alongside these clear health benefits, Tamoxifen has a long list of possible side-effects and possible interactions. It is known to act as a blood-thinner so may cause clinical complications of strokes or emboli. There are also concerns around using the drug when pregnant or breastfeeding, and the wide range of milder side effects which users may discover - such as rashes, breathing difficulties, bleeding and bruising (among others.)

Last Reviewed:
December 22, 2017
Last Updated:
April 26, 2018
Content Source: