If you have prostate cancer or certain other conditions, your doctor might suggest Zoladex (goserelin) as a treatment option for you. Along with other questions you may have about the drug, you could be wondering about its side effects.

Zoladex is a prescription drug that’s used in adults to treat the following conditions:

  • prostate cancer that hasn’t spread to areas outside of the prostate
  • advanced prostate cancer, which is cancer that has spread from the prostate to other parts of the body
  • advanced breast cancer, which is cancer that has spread from the breast to other parts of the body
  • endometriosis, a condition in which tissue grows abnormally outside of the uterus
  • abnormal menstrual bleeding

For abnormal menstrual bleeding, Zoladex is used in the short term before endometrial ablation. (This is a procedure that removes the lining of the uterus.) For its other uses, Zoladex is usually a long-term treatment.

For more information about Zoladex, including details about its uses, see this in-depth article on the drug.

Zoladex comes as an implant that’s inserted under the skin. A healthcare professional will insert one implant every 4 or 12 weeks. This depends on the condition you’re using Zoladex to treat and your dosage.

Like other drugs, Zoladex can cause mild or serious side effects. Read on to learn more.

Some people may experience mild or serious side effects during their Zoladex treatment. Examples of Zoladex’s commonly reported side effects include:

These are just a few of the more common side effects reported by people who took Zoladex in studies. These side effects can vary, depending on what condition the drug is being used to treat.

More common side effects of Zoladex for prostate cancer include:

  • hot flashes
  • ED
  • trouble passing urine

More common side effects of Zoladex for endometriosis, advanced breast cancer, or abnormal menstrual bleeding include:

* To learn more about this side effect, see “Side effects explained” below.

Mild side effects of Zoladex can vary, depending on what condition the drug is being used to treat.

Examples of mild side effects that have been reported with Zoladex for prostate cancer include:

Examples of mild side effects that are possible with Zoladex treatment for endometriosis, breast cancer, or abnormal menstrual bleeding include:

* To learn more about this side effect, see “Side effects explained” 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.

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. And don’t stop using Zoladex unless your doctor recommends it.

Zoladex may cause mild side effects other than the ones listed above. See the Zoladex patient information for the 3.6-milligram (mg) implant or the 10.8-mg implant for details.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks and reviews side effects of the medication. If you’d like to notify the FDA about a side effect you’ve had with Zoladex, visit MedWatch.

Less commonly, serious side effects have occurred in some people who used Zoladex. Serious side effects that have been reported with Zoladex include:

* To learn more about this side effect, see “Side effects explained” below.

If you develop serious side effects while using Zoladex, 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.

Learn answers to some frequently asked questions about the side effects of Zoladex.

Are any of Zoladex’s side effects long term?

Yes. Although less common, Zoladex can cause long-term side effects.

In studies, Zoladex was shown to decrease bone mineral density (BMD) in some people. Low BMD can increase your risk for osteoporosis (thinning bones). Osteoporosis may, in turn, increase your risk for bone fractures, even after you stop using Zoladex.

Other side effects that may affect you long term include an increased risk of cardiovascular problems, such as heart attack and stroke.

To learn more about possible long-term side effects of Zoladex, talk with your doctor.

Will I have fewer side effects with the 3.6-mg implant than the 10.8-mg implant? Are the possible side effects different?

It’s unlikely. Both strengths of Zoladex seem to cause similar side effects.

A study compared the safety and effectiveness of the drug for advanced breast cancer in females* who hadn’t gone through menopause. The results showed that the effects of the drug were the same, whether it was given as a monthly 3.6-milligram (mg) implant or as a 10.8-mg implant every 3 months.

If you have questions about side effects due to Zoladex dosage, talk with your doctor.

* 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.

Will I have side effects if I stop my Zoladex treatment?

It’s possible. Zoladex is an implant that a healthcare professional inserts under your skin. It’s designed to dissolve over time, and your doctor will explain your implant schedule to you.

If you develop a rare but serious allergic reaction or side effect, your doctor will likely remove the implant. Removal of the implant may cause temporary pain around the implant site.

If your reaction isn’t severe, your doctor may let the Zoladex implant dissolve on its own. It dissolves around 4 weeks after insertion, but its effects last up to 12 weeks in your system. During this time, you may notice changes as your hormone production increases to your natural level.

When stopping (or “coming off”) Zoladex, the effects that result can vary, depending on why you were using Zoladex.

If you have prostate cancer, stopping Zoladex could worsen symptoms of your condition.

If you’re a female* who hasn’t gone through menopause, it’s likely that your period will stop during Zoladex treatment. When you end Zoladex treatment, your period should return within 12 weeks.

If you have questions about ending your treatment with Zoladex, talk with your doctor.

* 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.

Do Zoladex’s side effects vary, depending on the condition it’s used to treat (prostate cancer, endometriosis, or breast cancer)?

Yes, some of the common side effects of Zoladex vary, depending on the condition being treated.

For example, mood changes and depression are more common side effects in people having the treatment for endometriosis or breast cancer. Mood-related side effects weren’t commonly reported in studies of the drug for prostate cancer.

For more information, see “More common side effects” above. If you have questions about the side effects that Zoladex can cause for people with your condition, talk with your doctor.

How soon do side effects of Zoladex start?

Zoladex releases goserelin, its active drug, very slowly for the first 8 days after it’s implanted under your skin. During this first week, you may notice injection site injuries, such as pain or bruising, where Zoladex was inserted.

For some people with breast cancer or prostate cancer, Zoladex can cause a short-term increase in tumor growth. This may happen when they first start using the drug. Worsening of cancer symptoms, such as bone pain, may occur during the first few weeks after Zoladex is implanted.

Zoladex works to lower the amount of sex hormone (testosterone or estrogen) in your body. After your first Zoladex implant, it takes 2 to 4 weeks for your hormone levels to drop.

Many of Zoladex’s side effects, such as hot flashes, acne, and sexual problems, are related to this hormone level drop. As a result, you may notice most of Zoladex’s side effects starting within 2 to 4 weeks.

Learn more about some side effects that Zoladex may cause.

Depression

Depression was reported as a common side effect of Zoladex. Specifically, it was reported in studies of the drug for treating breast cancer, endometriosis, and abnormal menstrual bleeding.

Symptoms of depression may last for 2 weeks or longer and often include:

  • feelings of sadness or hopelessness
  • loss of interest in your favorite activities
  • lack of energy or motivation
  • trouble concentrating
  • changes in your usual appetite or sleep patterns

What might help

If you or your loved ones notice that you have symptoms of depression, talk with your doctor. They may suggest one or more treatment options that can help ease depression, such as:

  • antidepressant medications
  • talk therapy with a licensed counselor or psychologist
  • in-person or online support groups for people with your condition
  • regular physical exercise, as recommended by your doctor

Injection site injuries

Injection site injuries are less common but possible side effects of Zoladex. Because Zoladex is an implant, you may develop reactions at the spot where it’s placed under your skin.

Skin-related injection site symptoms may include:

  • pain or irritation at the insertion site
  • bruising, or blood collecting under your skin
  • severe bleeding

It’s possible to develop serious symptoms after receiving a Zoladex implant. You should call your doctor right away if you have any of the following side effects:

You may have an increased risk for these side effects if you have a low body mass index or if you’re taking blood-thinning medications. Your doctor will monitor you carefully during and after your Zoladex implant is inserted.

What might help

Skin-related injection site injuries are temporary and usually go away on their own. To ease pain at the implant site, it may help to take an over-the-counter pain reliever, such as acetaminophen (Tylenol).

You could also ask whether you can have an ice pack applied to the insertion area beforehand. In a study, applying an ice pack for a short period significantly reduced the pain of a Zoladex injection.

If you have concerns about injection site injuries with Zoladex, talk with your doctor.

Weight gain

In studies, weight gain was reported as a side effect of Zoladex, but it wasn’t common.

Increased appetite and fluid retention have also been reported in people receiving Zoladex treatment. It isn’t known if these side effects are related to weight gain caused by using the drug.

What might help

If you notice that you’re gaining weight during Zoladex treatment, talk with your doctor. They may be able to help you identify contributing factors. They may also recommend ways to maintain a healthy weight, such as changing your diet or exercise routines.

Allergic reaction

Like most drugs, Zoladex can cause an allergic reaction in some people.

Symptoms can be mild or serious and can include:

  • skin rash
  • itchiness
  • flushing (temporary warmth, redness, or deepening of skin color)
  • swelling under your skin, typically in your eyelids, lips, hands, or feet
  • swelling of your mouth, tongue, or throat, which can make it hard to breathe

What might help

If you have mild symptoms of an allergic reaction, such as a mild rash, call your doctor right away. To manage your symptoms, they may suggest an over-the-counter antihistamine that you take by mouth, such as Benadryl (diphenhydramine). They may also suggest a product that you apply to your skin, such as hydrocortisone cream.

If your doctor confirms that you had a mild allergic reaction to Zoladex, they’ll decide if you should continue using it.

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 that you had a serious allergic reaction to Zoladex, they may have you switch to a different treatment.

Keeping track of side effects

During your Zoladex treatment, consider keeping notes about any side effects you’re having. Then, you can share this information with your doctor. This is especially helpful when you first start taking new drugs or using a combination of treatments.

Your side effect notes can include things such as:

  • what dose of drug you received when you had the side effect
  • how soon after starting that dose you had the side effect
  • what your symptoms were from the side effect
  • how it affected your daily activities
  • what other medications you were also taking
  • any other information you feel is important

Keeping notes and sharing them with your doctor will help them learn more about how Zoladex affects you. Your doctor can use this information to adjust your treatment plan if needed.

Zoladex 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 receive Zoladex. The list below includes some factors to consider.

Heart problems. Although it isn’t common, Zoladex can cause abnormal heart rhythms, heart attack, or stroke. If you already have heart disease, Zoladex treatment can further increase these risks. Before starting Zoladex, talk with your doctor about your past or current heart problems. They may suggest a different treatment option for you.

Diabetes. Zoladex can cause high blood sugar levels. If you have diabetes, Zoladex may make it harder to manage your blood sugar. As a result, your doctor may suggest changes to your diabetes treatment plan or blood sugar monitoring.

Bone problems. If you have osteoporosis (thinning bones), Zoladex treatment can possibly worsen your condition. Because of this, your doctor may use X-rays or bone scans to monitor your bone mineral density.

Allergic reaction. You shouldn’t use Zoladex if you’ve had an allergic reaction to it or any of its ingredients. You also shouldn’t use Zoladex if you’ve had an allergic reaction to a drug that’s similar to it. Before starting Zoladex treatment, be sure to tell your doctor about any allergic reactions you’ve had in the past. They can tell you about other medications that may be better options for you.

Alcohol use and Zoladex

For most people, occasional or moderate alcohol use is safe during Zoladex treatment.

But long-term alcohol use can increase the risk of bone loss. Zoladex treatment may increase this risk, especially in people who already have osteoporosis.

If you drink alcohol, talk with your doctor about how much is safe for you to consume while using Zoladex.

Pregnancy and breastfeeding while using Zoladex

It’s unsafe to use Zoladex during pregnancy.* Zoladex may cause harmful effects to a developing fetus or increase the risk of miscarriage.

If you’re able to become pregnant, talk with your doctor about birth control. It’s recommended that you use nonhormonal birth control during Zoladex treatment and for 12 weeks after the treatment ends.

It’s not recommended that you use Zoladex while breastfeeding.* This is because the effects of Zoladex on a breastfed child aren’t known.

If you’re pregnant or breastfeeding, talk with your doctor before starting Zoladex. They’ll recommend the best treatment plan for you during this time.

* Zoladex shouldn’t be used in someone who is pregnant or breastfeeding except during palliative treatment of advanced breast cancer. (Palliative treatment eases symptoms of a disease but doesn’t cure the disease itself.) If you have questions about these risks, talk with your doctor.

Most people using Zoladex have only mild side effects, and many of its common side effects can be easily managed. But serious side effects have also occurred.

Before you start Zoladex treatment, it’s important to talk with your doctor about the risk of side effects. Here are some questions to get your conversation started:

  • Do I have a higher risk for side effects of Zoladex than other people?
  • What can I do to lower my risk for serious side effects from Zoladex?
  • Are there ways to ease the side effects of Zoladex, such as hot flashes?
  • Do my other medications increase my risk for side effects from Zoladex?

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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.