Fulvestrant (Faslodex®)

Fulvestrant is a hormonal therapy drug used to treat advanced breast cancer. It’s best to read this with our information about breast cancer.

Fulvestrant is given as injections into the muscle (intramuscular) in the buttocks. You usually have it as an outpatient. Your cancer doctor or nurse will tell you how often you will have it.

Like all hormonal therapy drugs, fulvestrant can cause side effects. Some of these can be serious. It is important to read the detailed information below so that you know what to expect. The effects of hormonal therapy vary from person to person. Your healthcare team can tell you more and give you advice on how to manage any side effects.

Tell your doctor or nurse straight away if you feel unwell or have severe side effects, including any we do not mention here. If you need medical attention for any reason other than cancer, always tell the healthcare staff that you are having this treatment.

How fulvestrant works

Fulvestrant is a hormonal therapy drug. It is used to treat advanced breast cancer.

Hormones are substances produced naturally in your body. They act as chemical messengers and help control the activity of cells and organs. Hormonal therapies are drugs that affect how hormones are made or how they work in the body.

Many breast cancers need the hormone oestrogen to grow. This is called oestrogen-receptor positive (ER positive) breast cancer. These cancers have receptors (proteins) on the breast cancer cells. The receptors let hormones, such as oestrogen, attach to the cell.

Fulvestrant blocks the receptors and stops oestrogen reaching the cancer cells. This slows down or stops the cancer cells from growing. Fulvestrant also reduces the number of receptors on the breast cancer cells.

When fulvestrant is given

Fulvestrant is used to treat breast cancer that has spread. It is given to treat breast cancer in women who have been through the menopause. Sometimes it is given to treat breast cancer in men. It is usually given if other hormonal therapies have stopped controlling the cancer.

Your cancer doctor or nurse will explain how long you should take fulvestrant for. You usually have it for as long as it is effective in controlling the cancer.

How fulvestrant is given

You are given fulvestrant as two injections into muscle (intramuscular), one in each buttock. The injections are given one after the other. Each one takes 1 to 2 minutes.

You have the injections once a month. You have one extra dose two weeks after the first dose. You can have the injections at the hospital or they can be given at your GP surgery by your GP or practice nurse. If you are not able to visit the surgery, a district nurse may give you the injection at home.

If you sometimes delay an injection by a day or two it will not make much difference. But it is important to make sure you have your injections every month as prescribed.

Possible side effects of fulvestrant

We explain the most common side effects of fulvestrant here. We also include some rarer side effects. You may get some of the side effects we mention, but you are very unlikely to get all of them. If you are having other drugs as well, you may have some side effects that we do not list here.

You will see a doctor or nurse regularly while you have this treatment. Always tell your doctor or nurse about the side effects you have. They can prescribe drugs to help control some side effects and give you advice about managing them.

More information about this drug

We are not able to list every side effect for this treatment here, particularly the rarer ones. For more detailed information you can visit the electronic Medicines Compendium (eMC).

Allergic reaction

Sometimes fulvestrant can cause an allergic reaction. Signs of a reaction can include:

  • a rash
  • feeling itchy
  • wheezing
  • shortness of breath
  • swelling of your face or lips
  • feeling unwell. 

Tell your doctor or nurse straight away if you have any of these symptoms. If you develop any of these symptoms after you get home, contact the hospital straight away on the numbers you have been given or go to the nearest accident and emergency department.

Feeling or being sick, and losing your appetite

Let your doctor or nurse know if you are feeling or being sick. Your doctor can prescribe drugs to control this. We have more information about coping with a poor appetite that may help too.

Injection site

You may have some pain, redness and swelling around the area that was injected. Let your doctor know if this happens. Painkillers may help.

Tiredness and lack of energy

When you start taking fulvestrant, you may feel tired or sleepy or feel that you have no energy. Try to pace yourself until this improves. It is important to balance having enough rest with being physically active. Even regular short walks will help you to feel less tired. If you feel sleepy, do not drive or operate machinery.

Changes in the way your liver works

Fulvestrant may cause changes in the way your liver works. You are very unlikely to notice any problems but you will have regular blood tests to check your liver is working properly.

Hot flushes and sweats

These are often mild but this can vary. During a hot flush, you feel warmth in your neck and face and your skin may redden. Mild flushes can last for a few seconds or minutes. More severe flushes can last for 10 minutes or more. You may have sweats and then feel cold and clammy. Some people feel anxious or irritable during a hot flush.

There are things you can do to try to reduce hot flushes, such as cutting down on nicotine, alcohol and hot drinks with caffeine in them, like tea and coffee.

Your doctor can prescribe drugs to help reduce hot flushes.

Hot flushes may improve after the first few months.


This is usually mild. If it does not get better, your doctor can prescribe drugs to control diarrhoea. Make sure you drink at least two litres (three and a half pints) of fluids every day if you have diarrhoea.


If you have headaches, let your doctor or nurse know. They can usually be controlled with painkillers.

Back, joint or muscle pain

You may have back pain or pain in your joints or muscles. Let your doctor and nurse know if this happens. They can prescribe painkillers and give you advice. Tell them if it does not get better.

Skin rashes

You may get a mild rash. Tell your doctor or nurse if this happens. It is very important to contact your doctor straight away if you get a severe skin rash.

Urine infection

Fulvestrant can make you more likely to get a urine infection. Let your doctor know if you have pain or discomfort when you pass urine, if you need to go more often or if your urine is cloudy or smelly. Your doctor may prescribe antibiotics.

Less common side effects

Blood clots (thrombosis)

Fulvestrant slightly increases the chances of a blood clot. A clot can cause symptoms such as:

  • pain
  • redness and swelling in a leg or arm
  • breathlessness
  • chest pain. 

Contact your doctor straight away if you have any of these symptoms. A blood clot is serious but your doctor can treat it with drugs that thin the blood. Your doctor or nurse can give you more information.

Vaginal bleeding or discharge

Some women may have vaginal bleeding. If this happens it is usually in the first few weeks of treatment. Or it may happen when you change from another hormonal therapy to fulvestrant. If it continues for more than a few days tell your doctor or nurse.

Another uncommon side effect is a white vaginal discharge or sometimes vaginal thrush. Tell your doctor if you have this.

Bruising and bleeding

Fulvestrant can reduce the number of platelets in your blood. Platelets are cells that help the blood to clot. Tell your doctor if you have any bruising or bleeding you cannot explain. This includes nosebleeds, bleeding gums, blood spots or rashes on the skin.

Always let your doctor or nurse know about any side effects you have, as there are usually ways in which they can be controlled or improved.

Other information about fulvestrant

Other medicines

Some medicines, including ones you can buy in a shop or chemist, can affect fulvestrant or be harmful when you are having fulvestrant. Tell your doctor about any medicines you are taking, including over-the-counter drugs, complementary therapies and herbal drugs.

Let your doctor know if you are taking drugs that thin the blood, such as warfarin. Because fulvestrant is given by injection, it can cause some bleeding under the skin if you are taking this type of drug.


The injection contains alcohol. Tell your doctor, nurse or pharmacist if this is a problem for you. This may be harmful for people who have alcoholism.

Medical or dental treatment

If you need to go into hospital for any reason other than cancer, always tell the doctors and nurses that you are taking fulvestrant. Explain you are taking a hormonal therapy and that no one should stop or restart it without advice from your cancer doctor. Tell them the name of your cancer doctor so they can ask for advice.

Always tell your dentist you are taking fulvestrant before having any dental treatment.


Your doctor will advise you not to become pregnant or to father a child during treatment. This is because the drugs may harm a developing baby. It is important to use contraception during, and for a few months after, treatment. You can talk to your doctor or nurse about this.


Women are advised not to breastfeed during treatment and for a few months after. This is in case there is fulvestrant in their breast milk.