Myfembree (relugolix/estradiol/norethindrone) is a prescription drug used to manage heavy periods caused by uterine fibroids. Myfembree can cause side effects that range from mild to serious, including menstrual cycle changes and hair loss.

Specifically, Myfembree is prescribed for adult females* who haven’t gone through menopause to help manage:

Myfembree treatment should not last longer than 24 months, as this may cause irreversible bone loss.

Myfembree comes as an oral tablet. It contains the active ingredients relugolix, estradiol, and norethindrone acetate.

Keep reading to learn about common, mild, and serious side effects Myfembree can cause. For a general overview of the drug, including details about its uses, see this article.

* 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.

Myfembree has a boxed warning. This is the most serious warning from the Food and Drug Administration (FDA). For details, see the “Side effects explained” section below.

Some people may experience mild to serious side effects during Myfembree treatment. Examples of the drug’s commonly reported side effects include:

Mild side effects have been reported with Myfembree. These include:

In most cases, these side effects should be temporary. And some may be easily managed. But if you have symptoms that are ongoing or bothersome, talk with your doctor or pharmacist. And do not stop taking Myfembree unless your doctor recommends it.

Myfembree may cause mild side effects other than those listed above. See the drug’s prescribing information for details.

Serious side effects have been reported with Myfembree. These include:

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

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

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 Myfembree, visit MedWatch.

Allergic reaction

For some people, Myfembree can cause an allergic reaction. But it isn’t clear how often this occurred in the drug’s studies.

In general, symptoms of allergic reaction can be mild or serious. You can learn more about possible symptoms in this article.

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 Myfembree.

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 Myfembree, they may have you switch to a different treatment.

Get answers to some frequently asked questions about side effects of Myfembree.

Can Myfembree cause weight loss or weight gain?

It’s unlikely. Weight loss and weight gain were not reported in studies of Myfembree. If you’re concerned about changes in your weight while taking Myfembree, talk with your doctor or pharmacist.

Can Myfembree cause you to stop or miss your period?

It’s possible. Changes in menstrual bleeding patterns were reported in the drug’s studies. These changes can affect bleeding amount, intensity, and duration.

Myfembree can cause shorter, lighter, or missed periods. But this drug does not prevent pregnancy, and it should not be taken if you’re pregnant.

Missed periods can be a sign of pregnancy. If you think you’re pregnant while taking Myfembree, let your doctor know immediately.

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

Blood clots and blood vessel disorders

Myfembree has a boxed warning for the risk of blood clots and blood vessel disorders. A boxed warning is the most serious warning from the FDA. It alerts doctors and patients about drug effects that may be dangerous.

In studies, Myfembree increased the risk of blood clots and blood vessel conditions such as stroke, pulmonary embolism, and deep vein thrombosis. These conditions can cause various symptoms, such as:

If you have certain risk factors for these conditions, your doctor will typically not prescribe Myfembree for you. Examples of these risk factors include:

  • being someone over the age 35 years who smokes
  • current or past history of blood clots
  • current or past history of blood clotting or blood vessel disorders
  • heart and blood vessel conditions, such as coronary artery disease
  • heart rhythm conditions, such as atrial fibrillation
  • high cholesterol
  • obesity
  • being over the age of 35 years and having certain headaches or migraine
  • high blood pressure that’s not well managed with medication

What might help

Talk with your doctor about your health conditions before starting Myfembree.

This drug should be stopped at least 4 to 6 weeks before certain surgeries. Tell your doctor about any surgeries you have planned.

Monitor yourself for any of the symptoms listed above. If you develop serious side effects while taking this medication, call your doctor right away. If the side effects seem life threatening or you think you’re having a medical emergency, immediately call 911 or your local emergency number.

Talk with your doctor if you have any additional questions about your blood clot risk while taking Myfembree.

Bone Loss

Bone loss was a serious side effect reported in studies of Myfembree. Typically, you’ll not experience any symptoms of bone loss in the early stages. Over time, bone loss that isn’t well managed can lead to osteoporosis (weakened bones) and fractures (broken bones).

Taking other drugs that cause bone loss during Myfembree treatment can increase your risk of developing bone loss. Examples of drug groups that cause bone loss include proton pump inhibitors and corticosteroids.

What might help

Your doctor will check your bone strength before and during your Myfembree treatment. They may recommend you take calcium and vitamin D supplements to help prevent bone loss. Your Myfembree treatment should not be longer than 24 months because of the risk of irreversible bone loss.

Keeping track of side effects

During your Myfembree treatment, consider taking notes on any side effects you’re having. You can then share this information with your doctor. This is especially helpful when you first start taking a new drug or using a combination of treatments.

Your side effect notes can include things such as:

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

Sharing notes with your doctor will help them learn more about how Myfembree affects you. They can then use this information to adjust your treatment plan if needed.

Below is important information you should consider before taking Myfembree.

Boxed warning: Risk of blood clots and blood vessel disorders

Myfembree has a boxed warning, which is the most serious warning from the FDA. For details, see the “Side effects explained” section above.

Other warnings

Myfembree can sometimes cause harmful effects in people with certain conditions. This is known as a drug-condition interaction. Other factors may also affect whether this drug is a good treatment option for you. Talk with your doctor about your health history before starting Myfembree. Be sure to tell them if any of the following factors apply to you:

  • osteoporosis
  • conditions that increase your risk of blood clots
  • diabetes
  • liver or gall bladder problems
  • cancers that are hormone sensitive, such as breast cancer
  • mood disorders, such as depression and anxiety
  • irregular vaginal bleeding
  • previous allergic reaction to Myfembree
  • pregnancy
  • breastfeeding
  • alcohol consumption

Help is out there

If you or someone you know is in crisis and considering suicide or self-harm, please seek support:

If you’re calling on behalf of someone else, stay with them until help arrives. You may remove weapons or substances that can cause harm if you can do so safely.

If you are not in the same household, stay on the phone with them until help arrives.

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.