Key takeaways

  • Faslodex (fulvestrant) is a prescription drug that’s used to treat certain kinds of breast cancer.
  • Faslodex can cause side effects that range from mild to serious.
  • Examples include injection site pain, fatigue, and increased levels of liver enzymes.

This drug is used to treat certain forms of advanced or metastatic breast cancer that are hormone receptor-positive (HR-positive) in some females.

The active ingredient in Faslodex is fulvestrant. (An active ingredient is what makes a drug work.) The drug comes as an injection.

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Keep reading to learn about the common, mild, and serious side effects that Faslodex can cause.

Some people may experience mild or serious side effects during their Faslodex treatment. Examples of more commonly reported side effects of Faslodex include:

  • injection site pain
  • nausea
  • bone pain
  • back pain
  • increased levels of liver enzymes in your blood

These side effects can vary depending on whether Faslodex is used along with other drugs, such as Kisqali (ribociclib), Ibrance (palbociclib), or Verzenio (abemaciclib).

For more information about some of these side effects, see “Tips for managing side effects.”

Faslodex can cause mild side effects in some people. Examples of mild side effects that have been reported with Faslodex include:

In most cases, these side effects should be temporary. And some may be easily managed, too. But if you have any symptoms that are ongoing or that bother you, talk with your doctor or pharmacist. And don’t stop using Faslodex unless your doctor recommends it.

Faslodex may cause mild side effects other than the ones listed above. See the Faslodex prescribing information for details.

Less commonly, Faslodex can cause serious side effects in some people. Serious side effects that have been reported with Faslodex include:

  • nerve damage near the injection site
  • very high levels of liver enzymes in the blood
  • bleeding or bruising easily

If you develop serious side effects while taking Faslodex, call your doctor right away. If the side effects seem life threatening or if you think you’re having a medical emergency, immediately call 911 or your local emergency number.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks and reviews side effects of the medication. Sharing your experience helps make medication safer for everyone by giving doctors and researchers more information about how the drug works in real life. If you develop a side effect while taking Faslodex and want to tell the FDA about it, visit MedWatch or call 800-FDA-1088.

Allergic reaction

For some people, Faslodex can cause an allergic reaction.

This side effect was reported in the drug’s studies.

In general, symptoms of an allergic reaction can be mild or serious.

What might help
If you have mild symptoms of an allergic reaction, such as a mild rash, call your doctor right away. They may suggest a treatment to manage your symptoms and can determine whether you should keep taking Faslodex.

If you have symptoms of a severe allergic reaction, such as swelling or trouble breathing, call 911 or your local emergency number right away. These symptoms could be life threatening and require immediate medical care.

If your doctor confirms you’ve had a serious allergic reaction to Faslodex, they may have you switch to a different treatment.

Get answers to some frequently asked questions about Faslodex’s side effects.

No, Faslodex shouldn’t cause weight gain. This wasn’t reported as a side effect of the drug in studies.

It’s more likely that Faslodex would cause weight loss than weight gain. This is because reduced appetite can be a side effect of the drug in some people.

Weight loss has been reported in some people who received Faslodex with Verzenio (abemaciclib).

Faslodex is meant to be used as a long-term treatment. Although not common, some side effects may be long term.

For example, Faslodex injections have been reported to cause damage to the sciatic nerve. This nerve is located near your buttocks. The muscle of your buttocks is where a healthcare professional injects the drug.

If this nerve is damaged, you could develop long-term sciatica-like symptoms. These include pain, numbness, and burning sensations that travel down the back of your leg.

If you have concerns about possible long-term side effects from Faslodex, talk with your doctor.

For most people, Faslodex’s side effects are mild and short term. Some side effects, such as injection site pain, typically reappear after you receive each dose. But these should ease a few days after your injections.

There may be things you can do to help make certain Faslodex side effects more manageable. If you have ongoing, worsening, or bothersome side effects, talk with your doctor or pharmacist. They can suggest tips for managing them or recommend other available treatment options for your condition.

Fatigue

Fatigue can be a common side effect of Faslodex.

When people used Faslodex by itself, fatigue was reported slightly more frequently with 500 milligrams (mg) of the drug than with 250 mg.

Fatigue is usually a mild side effect, but severe fatigue has been reported. In studies of Faslodex use with Ibrance (palbociclib) or Verzenio (abemaciclib), some people developed fatigue so severe that they stopped using these drugs.

What might help

If you’ve developed fatigue from Faslodex, it may improve on its own within a few days or weeks after a dose. If it doesn’t, here are a few tips that might help to ease your fatigue:

  • Make sure you get plenty of sleep. Aim for at least 7 to 8 hours of sleep each night. If you feel tired during the day, try taking a short nap.
  • Eat a balanced diet. Even if you don’t have much appetite, choose foods that are nutritious instead of foods with empty calories. For example, reach for vegetables or fruits instead of crackers or chips. Nutrient-rich foods can help give you more energy. If you’re not sure what to eat, talk with your doctor or a dietitian.
  • Get regular physical activity. You might think that exercise would make you feel more tired. But studies show that increased physical activity significantly reduces fatigue in people with breast cancer. If you can, go for a daily walk, or try another mild form of exercise. This may provide a boost of energy. Talk with your doctor about what types of exercise might be appropriate for you.

It’s important to note that breast cancer itself can cause fatigue. This is especially true for advanced and metastatic breast cancer. While these tips may help to ease fatigue, they may not make it go away completely.

Overall, Faslodex is an effective medication that may help to treat your cancer. While Faslodex can cause fatigue, the benefits of the treatment usually outweigh the risk of this side effect.

If you develop fatigue during Faslodex treatment, talk with your doctor. They may have other recommendations for treating this side effect.

Hair loss

Although rare, hair loss was reported as a side effect in people using Faslodex on its own.

When Faslodex is used with certain drugs to treat breast cancer, hair loss is a common side effect. Other drugs commonly prescribed with Faslodex include Kisqali (ribociclib), Ibrance (palbociclib), and Verzenio (abemaciclib).

What might help

Hair loss is a common side effect of many cancer treatments, but it’s usually not permanent. After you complete your treatment, your hair should grow back.

During Faslodex treatment, treating your hair gently may help reduce hair loss. This includes not brushing it too much or using styling tools that are harsh on your hair, such as a blow-dryer or curling iron. Avoid washing your hair every day. When you do, use a gentle, fragrance-free shampoo.

If you have questions about hair loss with Faslodex, talk with your doctor.

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. Be sure to talk with your doctor if any of the following apply to you:

  • bleeding disorders
  • use of blood thinners
  • liver problems
  • previous allergic reaction to this or a similar drug
  • pregnancy
  • breastfeeding

Alcohol and Faslodex

Alcohol isn’t known to cause any interactions with Faslodex.

But consuming too much alcohol can damage your liver. With liver damage or other liver problems, the usual dose of Faslodex may cause the drug to build up in your body.

If you drink alcohol, talk with your doctor about how much is safe to consume while you’re taking Faslodex.

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.