Fulvestrant (Faslodex)

Fulvestrant (pronounced full-vest-rant) is also called Faslodex. It is a treatment for breast cancer.

What is fulvestrant?

Fulvestrant is a hormone treatment for post menopausal Open a glossary item women with locally advanced or advanced breast cancer. You might have it with targeted cancer drugs, such as palbociclib or abemaciclib.

Sometimes it is used in pre menopausal women. In this situation, women have it with another hormone treatment called a luteinising hormone releasing hormone (LHRH) agonist and a targeted drug. 

How does fulvestrant work?

The female sex hormones oestrogen and progesterone stimulate some breast cancers to grow. These breast cancers are called hormone sensitive or hormone receptor positive.

Drugs that block the effects of these hormones can slow or stop the growth of breast cancer cells.

Fulvestrant stops oestrogen getting to the cancer cells by blocking oestrogen receptors and reducing the number of receptors the cancer cells have.  

How do you have fulvestrant?

You have fulvestrant as an injection into the muscle (intramuscular) in your bottom.

How often do you have fulvestrant?

You have fulvestrant as cycles of treatment. This means you have the drug and then a rest for your body to recover. Each cycle is 28 days (4 weeks).

On cycle 1 you have injections on day 1 and day 15.

After cycle 1 you have injections on day 1 of each cycle.

You have two injections – one into each buttock. You might have these in hospital as an outpatient, or at your GP surgery. Your doctor or practice nurse gives you the injections. Each injection takes 1 to 2 minutes.

You carry on with treatment until it stops working, and the side effects aren’t too bad.


You might have blood tests before starting treatment and during your treatment. They check your general health and might check your levels of blood cells and other substances in the blood.

What are the side effects of fulvestrant?

Side effects can vary from person to person. They also depend on what other treatment you are having. 

When to contact your team

Your doctor, nurse, or pharmacist will go through the possible side effects. They will monitor you closely during treatment and check how you are at your appointments. Contact your advice line as soon as possible if:

  • you have severe side effects 

  • your side effects aren’t getting any better

  • your side effects are getting worse

Early treatment can help manage side effects better.

We haven't listed all the side effects here. Remember it is very unlikely that you will have all of these side effects, but you might have some of them at the same time.

Common side effects

These side effects happen in more than 10 in 100 people (more than 10%). You might have one or more of them. They include:

Tiredness and weakness (fatigue)

You might feel very tired and as though you lack energy.

Various things can help you to reduce tiredness and cope with it, for example exercise. Some research has shown that taking gentle exercise can give you more energy. It is important to balance exercise with resting.

Feeling or being sick 

Feeling sick is usually mild. Anti sickness tablets can control it if you need them. Tell your doctor or nurse if you feel sick. 

Hot flushes and sweats 

We have some tips for coping with hot flushes and the possible treatments for men and women. Talk to your doctor if your hot flushes are hard to cope with. They might be able to prescribe you some medicines.

Soreness and swelling around the injection site

Tell your nurse if you notice any signs of redness or irritation around the injection site. Rarely you might have some bleeding or bruising at the injection sites.

This can last for 1 or 2 days after the injections. 

Liver changes 

You might have liver changes that are usually mild and unlikely to cause symptoms. They usually go back to normal when treatment finishes. You have regular blood tests to check for any changes in the way your liver is working.

Rarely you might have liver problems that change how well your liver is working.

Skin rash

Skin problems include a skin rash, dry skin and itching. This usually goes back to normal when your treatment finishes. Your healthcare team can tell you what products you can use on your skin to help.

Allergic reaction

You might have an allergic reaction when taking this drug. Symptoms can include a skin rash, itching, flushing, breathing problems, swelling of the face and throat, and dizziness due to low blood pressure. Rarely, some allergic reactions can be life threatening.

Tell your nurse or doctor straightaway if you notice any of these symptoms or go straight to  accident and emergency (A&E) if you have a reaction.

Musculoskeletal pain 

You might have pain in the muscles, back, bones, ligaments, tendons and nerves. Less commonly you might have pain along the sciatic nerve (Sciatica).

Occasional side effects

These side effects happen in between 1 and 10 out of every 100 people (between 1 and 10%). You might have one or more of them. They include:

  • headaches
  • loss of appetite
  • diarrhoea
  • increased risk of blood clots that can be life threatening; signs are pain, redness and swelling where the clot is. Feeling breathless can be a sign of a blood clot in the lung. Contact your advice line or doctor straight away if you have any of these.
  • urine infection – you might have smelly urine, pain when passing urine or needing to pass urine more often
  • vaginal bleeding, discharge, or a vaginal yeast infection (thrush)
  • bruising, bleeding gums or nosebleeds
  • numbness or tingling in your fingers or toes

Coping with side effects

We have more information about side effects and tips on how to cope with them.

What else do I need to know?

Other medicines, foods and drink

Cancer drugs can interact with some other medicines and herbal products. Tell your doctor or pharmacist about any medicines you are taking. This includes vitamins, herbal supplements and over the counter remedies.


This drug contains very small amounts of alcohol. This is not harmful to most people but may be harmful if you have alcohol problems.

Pregnancy and contraception

This drug may harm a baby developing in your womb. It is important not to become pregnant or father a child while you are having treatment with this drug and for 2 years afterwards. Talk to your doctor or nurse about effective contraception before starting treatment.

Loss of fertility

It is not known whether this treatment affects fertility in people. Talk to your doctor before starting treatment if you think you may want to have a baby in the future.


It is not known whether this drug comes through into the breast milk. Doctors usually advise that you don’t breastfeed during this treatment.

Treatment for other conditions 

If you are having tests or treatment for anything else, always mention your cancer treatment. For example, if you are visiting your dentist.

More information about this treatment

For further information about this treatment and possible side effects go to the electronic Medicines Compendium (eMC) website. You can find the patient information leaflet on this website.

You can report any side effect you have to the Medicines Health and Regulatory Authority (MHRA) as part of their Yellow Card Scheme.

  • Electronic Medicines Compendium 
    Accessed May 2021

  • Fulvestrant for hormone-sensitive metastatic breast cancer

    C Lee and others 

    Cochrane Database of Systematic Reviews 2017 1:CD011093

Last reviewed: 
22 Oct 2021
Next review due: 
22 Oct 2024

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