If you have a certain kind of cancer, your doctor might suggest Hydrea as a treatment option for you.

Hydrea is a prescription medication that’s used in adults with either of the following conditions:

  • Resistant chronic myeloid leukemia (CML). “Resistant” means a past treatment for the cancer worked at first, but the cancer is no longer responding to it.
  • Locally advanced head and neck cancer (excluding lip cancer). For this purpose, Hydrea is taken along with other chemotherapy drugs and radiation therapy.

The active ingredient in Hydrea is hydroxyurea. (An active ingredient is what makes a drug work.) Hydrea belongs to a group of cancer drugs called antimetabolites, which are a type of chemotherapy drug.

Hydrea comes as capsules that you swallow. If you and your doctor agree that Hydrea is safe and working well for you, you’ll likely take it long term.

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

Like other drugs, Hydrea can cause mild to serious side effects. It’s important to note that Hydrea has been on the market since 1967. At that time, drug studies were not as in depth as they are now. Because of this, many of the side effects described in this article were reported after the drug became available for use, rather than during studies of Hydrea.

Keep reading to learn more about Hydrea’s side effects.

Some people may experience mild or serious side effects during their Hydrea treatment.

Examples of Hydrea’s commonly reported side effects include:

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

These are just a few side effects Hydrea may cause. The following sections describe more of the possible side effects of this drug.

Like most medications, Hydrea can cause some mild side effects.

Examples of mild side effects that have been reported with Hydrea include:

  • low appetite
  • feeling dizzy or drowsy
  • fever or chills
  • hair loss
  • headache
  • pain while urinating
  • skin side effects, including:
    • thin skin or nail atrophy (nail thinning or loss)
  • swelling due to fluid retention, such as in your legs or feet
  • weakness
  • digestive problems*

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

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 bother you, talk with your doctor or pharmacist. And you should not stop taking Hydrea unless your doctor recommends it.

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

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

In some cases, serious side effects may occur during Hydrea treatment. Serious side effects that have been reported with Hydrea include:

If you develop serious side effects while taking Hydrea, 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.

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

What are Hydrea’s side effects when it’s used off-label to treat essential thrombocythemia?

Hydrea isn’t approved by the Food and Drug Administration (FDA) to treat essential thrombocythemia (also called primary thrombocythemia). But in some cases, the drug may be used off-label to treat this condition. (Off-label drug use is when an FDA-approved drug is prescribed for a purpose other than what it’s approved for.)

Hydrea’s side effects are expected to be the same when used for essential thrombocythemia as when it’s used to treat cancer.

Essential thrombocythemia is a disorder in which your body makes too many thrombocytes (also called platelets). Platelets are blood cells that help with blood clotting, such as after an injury.

If you’d like to learn more about off-label uses for Hydrea, talk with your doctor or pharmacist.

Can Hydrea cause sexual side effects?

It’s not likely. Sexual side effects, such as erectile dysfunction or low libido (sex drive), haven’t been reported in people taking Hydrea. If you have concerns about sexual side effects while taking Hydrea, talk with your doctor.

On a related note, low or no sperm count has been reported in males* taking Hydrea. This could affect fertility (the ability to conceive a child). To learn more, see the “Ask a pharmacist” section below.

* 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.

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

Hair loss

Some people have reported hair loss with Hydrea treatment. It’s not known exactly how often this side effect occurs.

It’s important to note that Hydrea may be used with other cancer treatments, such as radiation therapy and other chemotherapy drugs. (Hydrea is also a type of chemotherapy.) Chemotherapy drugs often cause hair loss.

What might help

If you’re concerned about hair loss from Hydrea or other cancer drugs you’re taking, talk with your doctor. They may recommend a medication to treat it, such as Rogaine (minoxidil). But you should not start taking other medications without talking with your doctor first. They’ll need to make sure any drugs you take won’t interact with Hydrea or your other medications.

Hemolytic anemia

Hydrea may cause hemolytic anemia in some people. This is a serious condition that affects your red blood cells.

Red blood cells help carry oxygen from your lungs to your heart and throughout your body. With hemolytic anemia, these cells are destroyed faster than they’re made. This can cause your levels of red blood cells to become too low.

Symptoms of hemolytic anemia can include:

What might help

If you think you’re having symptoms of hemolytic anemia, call your doctor. They can order blood tests to check for this condition.

If they confirm hemolytic anemia, your doctor can prescribe treatment for this side effect. They’ll also have you stop taking Hydrea and switch to a different treatment.

If you have questions about your risk of developing hemolytic anemia during your Hydrea treatment, talk with your doctor.

Low levels of certain blood cells

Taking Hydrea may cause low blood cell counts. It’s not known how often this occurs.

Low blood cell levels reported with Hydrea include:

In most cases, having a low blood cell count doesn’t cause symptoms. These problems are usually caught with blood tests. But in some cases, these conditions can cause symptoms such as:

  • feeling dizzy or lightheaded
  • frequent infection
  • fatigue
  • unusual bruising or bleeding
  • weakness

It’s important to note that people who’ve had chemotherapy or radiation therapy in the past have a higher risk for low blood cell levels from Hydrea.

What might help

Your doctor will order tests to check your blood cell levels before prescribing Hydrea. You’ll also have these blood tests done regularly during your treatment.

If your test results show that you have low blood cell counts, your doctor can prescribe treatment to raise these levels. Your doctor may also:

  • have you temporarily or permanently stop taking Hydrea
  • lower your Hydrea dose

In many cases, blood cell counts quickly return to their usual levels if you stop taking Hydrea. At that point, your doctor can determine whether it’s safe for you to resume treatment with Hydrea.

Your doctor may also have you take folic acid during your Hydrea treatment. This is to help prevent a type of anemia (low levels of red blood cells) that can occur with Hydrea.

If you have concerns about developing low levels of blood cells while taking Hydrea, talk with your doctor.

Severe lung problems

Hydrea treatment can cause severe lung problems. It’s not known how often this side effect may occur.

Lung problems that have been reported in people taking Hydrea include:

Symptoms of these lung problems include:

What might help

Let your doctor know right away if you experience symptoms of lung problems while taking Hydrea. If they confirm you have this side effect, your doctor will have you stop taking this medication. They’ll also likely prescribe corticosteroids, such as Rayos (prednisone), to treat your symptoms.

If you have questions about your risk of developing lung problems from taking Hydrea, talk with your doctor.

Allergic reaction

Like most drugs, Hydrea can cause an allergic reaction in some people. It’s not known exactly how often these reactions occur, but they have been reported.

Symptoms can be mild to serious and can include:

  • skin rash
  • itchiness
  • flushing (temporary warmth, redness, or deepening of skin color)
  • swelling under your skin, usually 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. They may suggest an over-the-counter oral antihistamine, such as Benadryl (diphenhydramine), or a topical product, such as hydrocortisone cream, to manage your symptoms.

If your doctor confirms you had a mild allergic reaction to Hydrea, they’ll decide if you should continue taking 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 you had a serious allergic reaction to Hydrea, they may have you switch to a different treatment.

Keeping track of side effects

During your Hydrea treatment, consider keeping 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 new drugs 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 it affected your daily activities
  • what other medications you were taking
  • any other information you feel is important

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

Hydrea 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 starting Hydrea. The list below includes factors to consider.

Breathing or lung problems. Hydrea can cause lung problems in some people. If you already have breathing or lung problems, such as chronic obstructive pulmonary disease (COPD), taking Hydrea could make your condition worse. You may also have a higher risk of developing new lung problems. Your doctor can determine whether Hydrea is safe for you to take.

Low levels of certain blood cells. Hydrea can cause low blood cell counts, such as low levels of platelets or red blood cells. Before taking Hydrea, be sure to let your doctor know if you’ve been told you have low blood cell counts. Your doctor will likely want to treat this condition before prescribing Hydrea for you.

Past treatment with radiation therapy. Hydrea may cause radiation dermatitis in people who have previously used radiation therapy. Your doctor can determine whether Hydrea is safe for you to take.

Allergic reaction. If you’ve had an allergic reaction to Hydrea or any of its ingredients, your doctor will likely not prescribe Hydrea. Ask them what other medications are better options for you.

Alcohol use and Hydrea

It should be safe to drink alcohol during your Hydrea treatment. But alcohol could worsen digestive problems caused by Hydrea, such as constipation or diarrhea. It may also raise your risk of having these side effects.

If you drink alcohol, talk with your doctor about how much may be safe to drink during your Hydrea treatment.

Pregnancy and breastfeeding while taking Hydrea

See below for details about taking Hydrea during pregnancy or while breastfeeding.

Taking Hydrea during pregnancy

Hydrea may not be safe to take while pregnant. If you can become pregnant, your doctor will likely have you take a pregnancy test to make sure you’re not pregnant before prescribing Hydrea for you.

Females* who can become pregnant and males* with a partner who can become pregnant should use birth control while taking Hydrea, and for:

  • at least 6 months after your last dose, for females
  • at least 1 year after your last dose, for males

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

Taking Hydrea while breastfeeding

Hydrea may not be safe to take while breastfeeding. The drug passes into breast milk, which may cause side effects in a breastfed child.

Your doctor will likely recommend that you do not breastfeed while taking Hydrea. If you’re currently breastfeeding or planning to breastfeed, talk with your doctor about your options.

Like most medications, taking Hydrea can cause side effects. This includes some serious side effects.

Before taking Hydrea, talk with your doctor. Ask questions to help you become familiar with this medication and its side effects. Some example questions to help get you started include:

  • How do side effects of Hydrea compare with other treatment options for my cancer?
  • Are there ways I can lower my risk of side effects from Hydrea?
  • Do other drugs I take raise my risk for side effects from Hydrea?
  • Does my medical history raise my risk of certain side effects from Hydrea?
  • If I have side effects while taking Hydrea, is there a lower dose I can try?

Q:

Will taking Hydrea affect my fertility?

Anonymous

A:

It’s possible. Hydrea may affect fertility (the ability to conceive a child) in males.

Hydrea can damage or destroy sperm and healthy cells in the testicles. Low or no sperm count has been reported in males taking Hydrea. This can result in fertility issues, including infertility.

These side effects sometimes go away when you stop taking the drug. But for some people, they don’t go away even after stopping Hydrea treatment.

If you’re concerned about fertility issues with Hydrea, be sure to talk with your doctor before you begin treatment. They can provide more information on sperm conservation (collecting and freezing a sperm sample), which could help you conceive in the future.

Note: 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.

The Healthline Pharmacist TeamAnswers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.

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.