If you have breast cancer, your doctor may prescribe Faslodex for you.

It’s a prescription drug that’s used in some cases to treat certain forms of breast cancer in adult females.* The forms include:

To learn more about these conditions and how Faslodex is used to treat them, see the “What is Faslodex used for?” section below.

* In this article, we use the term “female” to refer to someone’s sex assigned at birth. For information about the difference between sex and gender, see this article.

Faslodex basics

Faslodex comes as a liquid inside prefilled syringes. You’ll receive doses of Faslodex from a healthcare professional. They’ll inject the drug into your buttocks.

Faslodex contains the active drug fulvestrant. It’s a type of hormone therapy. Faslodex is also available as a generic drug called fulvestrant.

In this article, we describe how Faslodex is given, as well as its uses, side effects, and more.

Like most drugs, Faslodex may cause mild or serious side effects. The lists below describe some of the more common side effects that Faslodex may cause. These lists don’t include all possible side effects.

Keep in mind that side effects of a drug can depend on:

  • your age
  • other health conditions you have
  • other medications you may be taking

Your doctor or pharmacist can tell you more about the potential side effects of Faslodex. They can also suggest ways to help reduce side effects.

Mild side effects

Here’s a list of some of the mild side effects that Faslodex can cause. To learn about other mild side effects, talk with your doctor or pharmacist, or read Faslodex’s prescribing information.

Mild side effects of Faslodex that have been reported include:

Mild side effects of many drugs may go away within a few days or a couple of weeks. But if they become bothersome, talk with your doctor or pharmacist.

* For more information on this side effect, see the “Side effect focus” section below.

Serious side effects

Serious side effects from Faslodex can occur, but they aren’t common. If you have serious side effects from Faslodex, call your doctor right away. However, if you think you’re having a medical emergency, you should call 911 or your local emergency number.

Serious side effects of Faslodex that have been reported include:

* For more information on this side effect, see the “Side effect focus” section below.

Side effect focus

Learn more about some of the side effects Faslodex may cause.

Pain or other side effects at Faslodex injection sites

Pain or other side effects, such as nerve damage, may occur at Faslodex injection sites. (An injection site is the area of your body where the drug is injected.) Pain was a common side effect in studies of Faslodex.

Faslodex is usually injected into the muscle in each of your buttocks. In rare cases, Faslodex injections may cause nerve damage. The damage can occur if the injection affects your sciatic nerve. This is a large nerve that runs from your spine, through your buttock, and down the back of your leg.

What might help

Talk with your doctor if you have bothersome pain after receiving Faslodex injections. If you have weakness, tingling, or numbness around the injection site, be sure to talk with them right away. These could be symptoms of nerve damage.

Hair loss

Hair loss may occur with Faslodex treatment. In studies, hair loss was more common when Faslodex was used along with other breast cancer drugs than when Faslodex was used alone.

What might help

Talk with your doctor about ways to manage hair loss while using Faslodex.

Your doctor may suggest you use a cooling cap. This product lessens blood flow to your scalp, which can lower the amount of Faslodex that reaches your hair follicles (sacs under your skin that hold the roots of your hair). This may help reduce hair loss due to the drug.

Headache

Some people may have headaches while using Faslodex. This was a common side effect in studies of the drug.

What might help

You may be able to ease a headache. Try applying a heating pad or ice pack to your head for about 5 to 10 minutes several times a day. You may also get relief from a hot bath or shower.

Talk with your doctor or pharmacist about over-the-counter medications that may help with headaches. These drugs include ibuprofen (Advil, Motrin) and acetaminophen (Tylenol). Your doctor or pharmacist can tell you if it’s safe to take these medications with Faslodex.

Allergic reaction

Some people may have an allergic reaction to Faslodex. Although an allergic reaction wasn’t reported in clinical studies of Faslodex, it can still happen.

Symptoms of a mild allergic reaction can include:

  • skin rash
  • itchiness
  • flushing (temporary warmth, redness, or deepening of skin color)

A more severe allergic reaction is rare, but possible. Symptoms of a severe allergic reaction can include swelling under your skin, typically in your eyelids, lips, hands, or feet. They can also include swelling of your tongue, mouth, or throat, which can cause trouble breathing.

Call your doctor right away if you have an allergic reaction to Faslodex. But if you think you’re having a medical emergency, call 911 or your local emergency number.

Your doctor will explain how Faslodex will be given to you. They’ll also explain how much you’ll be given and how often. Below are commonly used dosages, but the dosage you receive will be determined by your doctor.

Receiving Faslodex

Faslodex comes as a liquid inside prefilled syringes. You’ll receive the drug as an injection into a muscle. A healthcare professional will give you the injections. You won’t give yourself injections of Faslodex.

Faslodex injection site

Faslodex is injected into the muscle in each of your buttocks.

Dosage

The usual dosage of Faslodex is 500 milligrams (mg). This is given as two injections of 250 mg, with one injection given into each gluteal muscle.

Here’s the typical dosing schedule for Faslodex. Your first three Faslodex doses are given on day 1, day 15, and day 29 during the first month. After that, you’ll receive Faslodex injections once a month.

Receiving Faslodex with other drugs

Your doctor may have you use Faslodex together with other breast cancer treatments. This is often done to help treat breast cancer more effectively.

Your doctor may prescribe treatment in addition to Faslodex when your cancer becomes advanced or is metastatic. (“Advanced” means cancer that has spread to areas of your body near your breast or the lymph nodes in your armpit. “Metastatic” means the cancer has spread outside of areas near your breast or the lymph nodes in your armpit.)

Whether your doctor prescribes additional treatment depends on the specific type of breast cancer you’re using Faslodex to treat.

Examples of other drugs your doctor may prescribe along with Faslodex include:

If you have questions about using Faslodex with other medications, talk with your doctor.

Questions about receiving Faslodex

Below are some questions that are often asked about Faslodex treatment.

  • What if I miss a dose of Faslodex? If you miss an appointment to receive your Faslodex injection, contact your doctor’s office right away. They’ll work with you to reschedule your appointment.
  • Will I need to use Faslodex long term? You may need to use Faslodex long term. But if your cancer worsens or you’re unable to tolerate the side effects of the drug, your doctor may stop your treatment. They’ll recommend the length of time that’s right for you to use Faslodex.
  • Should I take Faslodex with food? You can take Faslodex with or without food. But your doctor may have you use the drug together with other cancer drugs that should be taken with food. Talk with your doctor to find out if you should take your cancer treatments with food.
  • How long does Faslodex take to work? It can take several doses for Faslodex to begin treating your breast cancer. You probably won’t notice the drug working in your body. But your doctor will order tests to check whether Faslodex is working for you.
Questions for your doctor

You may have questions about Faslodex and your treatment plan. It’s important to discuss all your concerns with your doctor.

Here are a few tips that might help guide your discussion:

  • Before your appointment, write down questions such as:
    • How will Faslodex affect my body, mood, or lifestyle?
  • Bring someone with you to your appointment if doing so will help you feel more comfortable.
  • If you don’t understand something related to your condition or treatment, ask your doctor to explain it for you.

Remember, your doctor and other healthcare professionals are available to help you. They want you to get the best care possible. So, don’t be afraid to ask questions or offer feedback on your treatment.

Find answers to some commonly asked questions about Faslodex.

How effective is Faslodex?

Faslodex is effective for treating certain types of breast cancer. To learn how Faslodex performed in clinical studies, see the drug’s prescribing information.

If you have questions about the effectiveness of Faslodex, talk with your doctor.

How does Faslodex work? And how long does it stay in your system after it’s been injected?

The drug Faslodex works by affecting a hormone called estrogen. (How a drug works is called its mechanism of action.)

Estrogen can stimulate cancer cells, which may cause breast cancer. Faslodex reduces the activity of estrogen and helps prevent it from stimulating cancer cells.

One way to find out how long Faslodex stays in your system is to measure its half-life. The half-life of a drug is the time it takes for half of the drug to leave your body.

The half-life for Faslodex is about 40 days. In other words, it takes about 40 days for your body to get rid of half of a dose of Faslodex.

It usually takes about four to five half-lives for a drug to leave your system. For Faslodex, this means the drug can stay in your system for up to 200 days after your last dose.

If you have other questions about how Faslodex works or how long it remains in your body, talk with your doctor or pharmacist.

Does Faslodex cause weight gain?

Weight gain wasn’t a side effect reported in studies of Faslodex.

But keep in mind that cancer often causes weight loss. So if you gain weight after you start Faslodex treatment, it could be a sign that your cancer is improving. The weight gain may not be caused by Faslodex itself.

If you experience weight gain while receiving Faslodex, talk with your doctor. They can suggest healthy ways for you to manage your weight.

Is Faslodex ever used with Xgeva or Zometa?

Yes, in some cases, your doctor may prescribe Faslodex along with (denosumab) Xgeva or (zoledronic acid) Zometa.

Xgeva is a drug that helps prevent and treat bone problems in people with cancer. You may need to use Xgeva if your breast cancer has spread into your bones.

Zometa is a drug that helps prevent bone loss.

Faslodex works by lessening the activity of estrogen in your body. A low estrogen level can lead to bone loss. So, your doctor may prescribe Faslodex together with Zometa to help prevent bone loss.

If you have questions about using Xgeva or Zometa with Faslodex, talk with your doctor.

Is Faslodex a chemotherapy drug or an aromatase inhibitor?

No, Faslodex isn’t a chemotherapy drug or an aromatase inhibitor, which is also a kind of drug. Faslodex is a type of hormone therapy.

Chemotherapy works by killing the cells in your body that multiply quickly. Although cancer cells usually multiply faster than healthy cells, some healthy cells do quickly multiply. Therefore, chemotherapy can affect both cancer cells and healthy cells.

Aromatase inhibitors work by lowering estrogen levels in your body, which helps stop breast cancer from growing. Aromatase inhibitors do this by stopping the activity of a certain enzyme (protein). The enzyme normally helps your body form estrogen.

As a type of hormone therapy, Faslodex works differently from aromatase inhibitors. For details, see “How does Faslodex work?” above.

Will I need to store Faslodex?

No, you won’t need to store Faslodex.

You’ll receive doses of Faslodex from a healthcare professional. You won’t need to store the drug at home.

Costs of prescription drugs can vary depending on many factors. These factors include what your insurance plan covers and which pharmacy you use. To find current prices for Faslodex injections in your area, visit GoodRx.com.

If you have questions about how to pay for your prescription, talk with your doctor or pharmacist. You can also visit the Faslodex manufacturer’s website to see if there are support options.

Faslodex is prescribed to treat certain kinds of breast cancer in adult females.*

Breast cancer is caused by rapidly growing breast cells. These cells can form a tumor in the breast and can also spread to other areas of the body.

Estrogen is a hormone that helps cancer cells grow. Faslodex is a type of hormone therapy that reduces the activity of estrogen in your body, which may help stop breast cancer from growing.

* In this article, we use the term “female” to refer to someone’s sex assigned at birth. For information about the difference between sex and gender, see this article.

Details on Faslodex’s uses

Faslodex is used for the following:

  • To treat advanced breast cancer that’s HR+. HR+ is short for hormone receptor-positive. With this kind ofbreast cancer, hormones cause your cancer to grow.
    • For this purpose, Faslodex is used in females who have gone through menopause and have received treatment with another hormone therapy.
  • To treat advanced breast cancer that’s HR+ and HER2-negative. “Advanced” means the cancer has spread to areas of your body near your breast or the lymph nodes in your armpit. HER2-negative is short for human epidermal growth factor receptor 2-negative. With this type of breast cancer, cancer cells don’t have HER2 proteins in them.
    • For this purpose, Faslodex is used in females who have gone through menopause and haven’t received treatment with another hormone therapy.
  • With ribociclib (Kisqali) to treat advanced or metastatic breast cancer that’s HR+ and HER2-negative. (“Metastatic” means the cancer has spread outside of areas near your breast or the lymph nodes in your armpit.)
    • For this purpose, Faslodex is used in females who have gone through menopause. The drug is used along with ribociclib (Kisqali). Faslodex can be used as a first hormone therapy or after your breast cancer has worsened after using another hormone therapy.
  • With abemaciclib (Verzenio) or palbociclib (Ibrance) to treat advanced or metastatic breast cancer that’s HR+ and HER2-negative.
    • For this purpose, Faslodex is used together with abemaciclib (Verzenio) or palbociclib (Ibrance) after your breast cancer has worsened following another hormone therapy.

Both Faslodex and anastrozole (Arimidex) are used to treat certain kinds of breast cancer in adult females.* Both drugs help stop breast cancer from growing by affecting the level of estrogen in your body.

If you’d like to learn more about these drugs, see this side-by-side comparison. You can ask your doctor for more information.

* In this article, we use the term “female” to refer to someone’s sex assigned at birth. For information about the difference between sex and gender, see this article.

The drugs Faslodex and letrozole (Femara) are both used to treat certain types of breast cancer in adult females.* Both drugs help stop the growth of breast cancer by affecting the level of estrogen in your body.

To see a detailed comparison of these drugs, check out this article. Then, talk with your doctor if you’d like to know more about these medications.

* In this article, we use the term “female” to refer to someone’s sex assigned at birth. For information about the difference between sex and gender, see this article.

Some important things to discuss with your doctor while considering Faslodex treatment include your overall health, any medical conditions you may have, and any drugs you take.

These considerations and others are described in more detail below.

Interactions

Taking medications, vaccines, foods, and other things with a certain drug can affect how the drug works. These effects are called interactions.

Before using Faslodex, be sure to tell your doctor about all medications you take, including prescription and over-the-counter types. Also describe any vitamins, herbs, or supplements you use. Your doctor or pharmacist can tell you about any interactions these items may cause with Faslodex.

Interactions with drugs or supplements

Faslodex isn’t known to interact with any drugs or supplements. The manufacturer of Faslodex didn’t look at interactions in studies of the drug.

But this doesn’t mean interactions can’t happen with Faslodex. Your doctor or pharmacist can tell you more about interactions that may occur with use of Faslodex.

Other interactions

Faslodex can cause the estrogen levels in your blood to appear higher than they are.

Your doctor may need to check your estrogen levels while you’re using Faslodex. To do this, they’ll usually order a saliva or urine test instead of a blood test. Saliva and urine tests for estrogen aren’t likely to be affected by Faslodex.

Warnings

Faslodex may not be right for you if you have certain medical conditions or other factors that affect your health. Talk with your doctor about your health history before you take Faslodex. Factors to consider include those in the list below.

Bleeding problems. Before starting Faslodex treatment, tell your doctor if you have any bleeding problems. This includes having low levels of platelets (a type of red blood cell that helps your blood clot). You may also have a higher risk of bleeding if you take blood thinners such as warfarin (Jantoven).

Bleeding is a possible side effect of Faslodex. So, if you already have bleeding problems, you may have a higher risk for this side effect while using the drug. Your doctor will watch you closely for bleeding during your treatment. Or they may prescribe a medication other than Faslodex.

Liver problems. Before using Faslodex, talk with your doctor about any liver problems you have, such as liver disease. Liver problems can increase the level of Faslodex in your body, which can raise your risk for side effects. Your doctor will usually inject a lower dose of Faslodex than usual if you have liver problems.

Allergic reaction. If you’ve had an allergic reaction to Faslodex or any of its ingredients, you shouldn’t take Faslodex. Ask your doctor what other medications are better options for you.

Faslodex and alcohol

It should be safe to drink alcohol during your Faslodex treatment. But keep in mind that drinking alcohol may make liver disease worse. So your doctor may have to inject a lower dose of Faslodex than usual if you have liver disease.

If you drink alcohol, talk with your doctor about the amount that’s safe for you to drink while using Faslodex.

Pregnancy and breastfeeding

It is not safe to use Faslodex while pregnant or breastfeeding.

Faslodex hasn’t been studied in pregnancy. But because of how the drug works in the body, it may cause harm to a fetus. To make sure you aren’t pregnant, your doctor may have you take a pregnancy test up to 7 days before starting treatment with Faslodex.

To help prevent pregnancy, females* using Faslodex should use an effective form of birth control while using the drug. And they should continue using birth control for at least 1 year after their last dose of Faslodex.

It isn’t known for sure if Faslodex can pass into breast milk during breastfeeding. To be safe, you shouldn’t breastfeed while using Faslodex, and for at least 1 year after your last dose.

If you’re pregnant or planning to become pregnant, talk with your doctor. You should also talk with your doctor if you’re breastfeeding or thinking about it. They may prescribe a drug other than Faslodex for you.

* In this article, we use the term “female” to refer to someone’s sex assigned at birth. For information about the difference between sex and gender, see this article.

If you have questions about using Faslodex for breast cancer, talk with your doctor or pharmacist.

You may also want to ask your doctor about other breast cancer treatments. This article on breast cancer treatment options can serve as a helpful guide.

Other questions you may want to ask your doctor about Faslodex include:

  • Will Faslodex interact with any other medications I take?
  • Will Faslodex keep working to treat my breast cancer after I stop using it?
  • Can I use Faslodex if I’m a male* with breast cancer?

To learn more about breast cancer and its treatment options, subscribe to Healthline’s breast cancer newsletter.

* In this article, we use the term “male” to refer to someone’s sex assigned at birth. For information about the difference between sex and gender, see this article.

Disclaimer: Healthline has made every effort to make certain that all information is factually correct, comprehensive, and up-to-date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.