Hydrea (hydroxyurea) is a brand-name prescription medication. It’s approved by the Food and Drug Administration (FDA) to treat certain forms of the following cancers in adults:

Hydrea is a type of chemotherapy that’s typically used as a long-term treatment.

Here are some fast facts about Hydrea:

  • Active ingredient: hydroxyurea
  • Drug class: antimetabolite
  • Drug form: oral capsule

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

Keep in mind that when Hydrea is prescribed for squamous cell carcinoma, the drug is used with radiation therapy and other chemotherapy. Some common, mild, and serious side effects may be due to these other treatments rather than Hydrea when taken at the same time. Your doctor can help determine which medications are causing side effects and what treatment plan is right for you.

Read on to learn about potential side effects of Hydrea. For a general overview of the medication, including details about its uses, see this article.

Hydrea can cause certain side effects, some of which are more common than others. These side effects may be temporary, lasting a few days to weeks. If the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

These are just a few of the more common side effects reported with Hydrea:

  • reduced appetite
  • sores in your mouth or throat
  • digestive side effects*
  • low levels of blood cells*

* For more information about this side effect, see “Side effect specifics” below.

Mild side effects can occur with Hydrea. This list doesn’t include all possible mild side effects of the drug. For more details, you can refer to Hydrea’s prescribing information.

Mild side effects that have been reported with Hydrea include:

  • reduced appetite
  • sores in your mouth or throat
  • headache
  • dizziness
  • sleepiness
  • feeling weak
  • difficult or painful urination
  • fever
  • chills
  • macrocytosis (red blood cells that are larger than usual)
  • digestive side effects*
  • skin or nail problems*

These side effects may be temporary, lasting a few days to weeks. If the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks side effects of the medication. If you develop a side effect while taking Hydrea and want to tell the FDA about it, visit MedWatch.

* For more information about this side effect, see “Side effect specifics” below.

Hydrea may cause serious side effects. The list below may not include all possible serious side effects of the drug. For more details, you can refer to Hydrea’s prescribing information.

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.

Serious side effects that have been reported with Hydrea and their symptoms include:

  • Severe skin ulcers (sores) and gangrene (tissue death). Symptoms can include:
    • open skin sores
    • pain, itching, swelling, or discoloration around the sore
    • flaking or scabbing around the sore
    • discharge or unpleasant odor from the sore
  • Low levels of blood cells.*
  • Other cancers.*
  • Lung problems.*
  • Allergic reaction.*†

* For more information about this side effect, see “Side effect specifics” below.
† An allergic reaction is possible after taking Hydrea. However, it’s not clear whether this side effect occurred in clinical trials.

Hydrea may cause several side effects. Here are some frequently asked questions about the drug’s side effects and their answers.

My doctor prescribed Hydrea off-label for essential thrombocythemia. What are the side effects?

There isn’t any information from clinical trials about the side effects of Hydrea when it’s taken for essential thrombocythemia. (This is a blood disorder in which your body produces too many platelets, which are cells that help your blood clot.) However, in general, side effects are likely to be the same as those reported with Hydrea for its approved uses.*

Essential thrombocythemia is not an approved use of Hydrea. Doctors may prescribe the drug off-label for this disorder. Off-label prescribing is when a doctor prescribes a drug for a use that the Food and Drug Administration (FDA) has not approved.

If you’d like to learn more about Hydrea for essential thrombocythemia and possible side effects, talk with your doctor.

* Hydrea is approved to treat certain forms of squamous cell carcinoma and chronic myeloid leukemia.

Should I expect hair loss with Hydrea?

Cases of hair loss have been reported since Hydrea became available for use. It’s not known how often this side effect occurs.

Some people may lose all their hair with Hydrea, while others may have some hair thinning. In either case, hair typically grows back after Hydrea treatment ends.

If you’re concerned about hair loss with Hydrea, talk with your doctor. They can recommend ways to help manage it.

Are nail and skin problems possible with Hydrea?

Yes. Nail and skin problems have occurred in people who took Hydrea. Examples of these problems include nail and skin darkening and thinning. In addition, some people reported skin peeling and raised purple or darkened patches of skin.

Serious skin problems have also been reported with Hydrea. These include skin cancer. To learn more, see “Other cancers” in the “Side effect specifics” section below. Other serious skin problems included severe skin ulcers and gangrene. To learn about the symptoms, see the “Serious side effects of Hydrea” section above.

If you have any concerns about nail or skin changes during Hydrea treatment, talk with your doctor.

Does Hydrea affect fertility?

It might. Hydrea can sometimes reduce sperm count in males.* This means the drug could decrease the ability to have a child who is biologically yours. However, in some cases, a low sperm count may rise after stopping Hydrea treatment.

It’s not known whether Hydrea affects fertility in females.* Fertility in females refers to the ability to become pregnant.

If you plan to have children in the future and are concerned about Hydrea’s possible effect on your fertility, talk with your doctor. They may recommend storing sperm or eggs for future use in fertility treatment.

* Sex and gender exist on spectrums. Use of the terms “male” and “female” in this article refers to sex assigned at birth.

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

Digestive side effects

Digestive side effects are commonly reported with Hydrea. They’re usually mild, but if not well-managed, they could lead to dehydration.

While taking Hydrea, you may have digestive side effects such as:

What you can do

If you have digestive side effects with Hydrea, it may help to take the medication with food. If this doesn’t help, talk with your doctor or pharmacist. They can suggest ways to help ease your symptoms. For example, they may recommend taking medication to ease nausea and vomiting. Depending on your symptoms, they may suggest antidiarrheal drugs to treat diarrhea or laxative medications for constipation.

It’s also important to drink plenty of fluids to avoid becoming dehydrated. If you experience vomiting or diarrhea, oral rehydration solutions such as Pedialyte or sports drinks such as Gatorade can be useful. The beverages also help replace electrolytes that you can lose with vomiting and diarrhea.

Here are some other tips for easing digestive side effects:

  • Eat little and often, rather than three main meals.
  • Try to avoid foods that are rich, spicy, greasy, or sugary.
  • Take frequent sips of water throughout the day.
  • Drink ginger or peppermint tea for nausea.

If you have digestive side effects that are severe or prevent you from eating or drinking as usual, talk with your doctor right away.

Low levels of blood cells

Low levels of blood cells may occur with Hydrea treatment. Blood cells are normally made in your bone marrow (the spongy material inside your bones). Hydrea can stop your bone marrow from producing as many blood cells as usual.

Hydrea commonly causes:

  • Low levels of white blood cells (cells that help your body fight infection). This is called leukopenia. Symptoms can include:
    • chills
    • sore throat
    • infection
  • Low level of platelets (cells that help your blood clot). This is called thrombocytopenia. Symptoms can include:
    • bruising easily
    • small red or purple spots on your skin
    • bleeding easily, such as having bleeding gums or nosebleeds
    • bleeding that takes longer than usual to stop
    • blood in your urine or stool
  • Low levels of red blood cells (cells that carry oxygen around your body). This is called anemia. Symptoms can include:
    • skin, gums, or nailbeds that are paler than usual
    • dizziness

Hydrea can also cause hemolytic anemia, which is a condition in which your red blood cells break down faster than your body can replace them. Along with the symptoms of anemia listed above, hemolytic anemia can cause jaundice and blood in your urine.

You’re more likely to have low levels of blood cells with Hydrea if you’ve had past radiation therapy or other forms of chemotherapy for your cancer. These treatments can cause low blood cell counts.

What you can do

It’s important to try to avoid getting infections while taking Hydrea. With fewer white blood cells, your body might not be able to fight infections as well as usual. Be sure to wash your hands often. Also, try to avoid crowds and people who are ill.

Before starting Hydrea treatment, ask your doctor if you should get any vaccinations to help prevent infections. Keep in mind that you should not get live vaccines while you’re taking Hydrea. This type of vaccine could cause serious infection if you have a low white blood cell count. For examples of live vaccines, see “Precautions for Hydrea” below.

Your doctor will order blood tests to check your blood cell levels before you start taking Hydrea and from time to time during treatment. Be sure to keep all your appointments for blood tests.

If you have any symptoms of low levels of blood cells such as those described above, see your doctor right away. They’ll likely order a blood test to check your levels.

If you have low blood cell levels, your doctor may reduce your Hydrea dose or have you stop taking Hydrea until your levels rise. They may also prescribe treatments to help increase your blood cell levels. If your blood cell levels don’t return to normal, you may need to stop taking Hydrea permanently.

Other cancers

Hydrea can increase the risk of developing a new cancer, such as leukemia or skin cancer. It’s not known how often new cases of cancer occur with the medication. Cases of leukemia and skin cancer occurred in people who took Hydrea for a long time.

Symptoms of cancer can include:

  • changes in your skin, such as new or changing moles, patches, or growths
  • skin sores that don’t heal
  • losing weight without meaning to
  • night sweats
  • unexplained fatigue
  • frequent infections
  • bruising or bleeding easily
  • swollen lymph nodes (in your neck, armpits, or groin, for example)
  • unusual lumps, bumps, or swellings that don’t go away

What you can do

While taking Hydrea, you can help reduce your risk of developing a new cancer by taking several steps. For example, try to minimize your exposure to sunlight. You can protect your skin from the sun with clothing, a hat, and sunscreen. Also avoid using tanning beds. In addition, try to maintain a weight that’s healthy for you and do not smoke.

If you develop new symptoms of cancer while taking Hydrea, see your doctor right away.

Lung problems

Hydrea can sometimes cause serious lung problems. It’s not known how often these side effects occurred in people who took the drug.

Examples of serious lung problems with Hydrea can include:

Symptoms of these lung problems can include fever, cough, breathlessness, wheezing, and trouble breathing.

What you can do

If you have symptoms of lung problems while taking Hydrea, see your doctor right away. They may prescribe medication such as corticosteroids. They’ll also likely recommend stopping Hydrea treatment.

Allergic reaction

As with most drugs, Hydrea can cause an allergic reaction in some people. However, it’s not clear how often allergic reactions occurred in people taking this drug.

Symptoms can be mild or serious and can include:

  • skin rash
  • itching
  • flushing
  • swelling under your skin, typically in your lips, eyelids, feet, or hands
  • swelling of your mouth, tongue, or throat, which can make it hard to breathe

What you can do

For mild symptoms of an allergic reaction, call your doctor right away. They may recommend ways to ease your symptoms and determine whether you should keep taking Hydrea. If your symptoms are serious and you think you’re having a medical emergency, immediately call 911 or your local emergency number.

Be sure to talk with your doctor about your health history before you take Hydrea. This drug may not be the right treatment for you if you have certain medical conditions or other factors that affect your health. The conditions and factors to consider include:

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 about other medications that may be better options for you.

Kidney or liver problems. If you have a kidney or liver problem, Hydrea could make it worse. Talk with your doctor about whether the drug is right for you. If you have a kidney problem, your doctor might prescribe a dosage of Hydrea that’s lower than usual.

Other cancer treatments. If you’ve had other cancer treatments, talk with your doctor about your risk of side effects with Hydrea. For example, ifyou have had radiation therapy or other chemotherapy, you may have an increased risk of low blood cell counts with Hydrea. Your doctor will likely order frequent blood tests to check your blood cells. If you have had radiation therapy, Hydrea could also worsen skin redness, discoloration, or discomfort you may have from that treatment.

If you have had interferon treatment, you may have an increased risk of severe skin ulcers with Hydrea. To read more about these side effects, see “Side effect specifics” above.

HIV. If you take certain HIV drugs, taking Hydrea may increase your risk of pancreatitis, liver problems, and peripheral neuropathy. Examples of these HIV medications include Retrovir (zidovudine) and Sustiva (efavirenz). If you’re receiving treatment for HIV, talk with your doctor about your risk of side effects with Hydrea.

Immunizations. Hydrea can weaken your immune system. The drug can also affect the way your body responds to vaccines. Before you start Hydrea treatment, it’s recommended that your vaccines are up to date. Talk with your doctor about this.

Keep in mind that you should not get live vaccines while taking Hydrea. Because your immune system may be weaker than usual, live vaccines could cause the infection they’re meant to protect you from. Examples of live vaccines include chickenpox, shingles, rotavirus, yellow fever, and the nasal spray flu vaccine (FluMist).

If you receive non-live (inactive) vaccines while taking Hydrea, your immune system might not respond to them as well as usual. This means that these vaccines might be less effective at protecting you from infection. Examples of non-live vaccines include tetanus, diphtheria, hepatitis B, meningitis, and COVID-19 (coronavirus) vaccines.

Alcohol and Hydrea

Alcohol isn’t known to interact with Hydrea. However, if you have certain side effects with Hydrea, drinking alcohol could make these worse. Examples of these side effects include nausea, vomiting, diarrhea, headache, dizziness, and drowsiness. In addition, if you have mouth sores from Hydrea, consuming alcohol could be painful.

If you drink alcohol, talk with your doctor about how much, if any, is safe to drink while you take Hydrea.

Pregnancy and breastfeeding while taking Hydrea

Here’s some information about pregnancy, breastfeeding, and Hydrea.

Pregnancy. Hydrea is not safe to take during pregnancy. If you’re able to become pregnant, your doctor will want you to have a pregnancy test before you start treatment. This is to confirm that you’re not pregnant.

If you’re pregnant or plan to become pregnant, talk with your doctor about other treatment options.

Females* who can become pregnant should use birth control while taking Hydrea and for 6 months after stopping treatment. Males* with a sexual partner who can become pregnant should use birth control while taking Hydrea and for 1 year after stopping treatment.

Breastfeeding. You should not breastfeed while taking Hydrea. This drug passes into breast milk and can cause serious side effects in a breastfed child. Talk with your doctor about healthy ways to feed your child during Hydrea treatment.

* Sex and gender exist on spectrums. Use of the terms “male” and “female” in this article refers to sex assigned at birth.

Most of Hydrea’s side effects are mild and easily managed. However, like most cancer treatments, this drug can also have some serious side effects, especially involving your blood cells. Be sure to talk with your doctor if you develop any serious side effects.

If you’d like to learn more about Hydrea, talk with your doctor or pharmacist. They can help answer any questions you have about side effects from taking the drug.

Besides talking with your doctor, you can do some research on your own. These articles might help:

Disclaimer: Medical News Today 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.