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What is hydroxyurea?

Hydroxyurea is an anti-cancer drug. It is used alone or with radiation therapy to treat some cancers, including chronic myeloid leukemia, head and neck cancers, and recurring or inoperable ovarian cancer.

This drug belongs to a class of medications called antimetabolites. In 1998, the FDA approved hydroxyurea to treat sickle cell anemia (also called sickle cell disease, or SCD).

You can only obtain hydroxyurea with a doctor’s prescription. It is available as a tablet or capsule.

Hydroxyurea is a generic medication, also available under the brand names Droxia, Siklos, and Hydrea.

What is hydroxyurea used to treat?

Hydroxyurea treats many types of head and neck cancers, including cancers of the cheek, tongue, mouth, tonsils, throat, and sinuses. It is also used to treat chronic myeloid leukemia, a white blood cell cancer.

The drug acts by stopping or slowing the growth of cancer cells in the body.

Hydroxyurea is also used to treat an inherited blood disorder called sickle cell anemia. Sickle cell anemia occurs when red blood cells are shaped abnormally, like a sickle. Hydroxyurea prevents sickle-shaped red blood cells from forming. 

How do you take hydroxyurea?

Wear disposable gloves when handling this medicine. Do not breathe in or touch this medicine with bare hands.

Swallow the capsule/tablet with a glass of water, with or without food. Do not break, crush, or chew the capsule. A tablet can only be broken if it has a scored line and your doctor advises you to do so. Wipe up any powder from the capsule or tablet with a wet paper towel and dispose of it in a closed container.

Take this tablet at the same time daily. Take the medicine exactly as prescribed. Your doctor will adjust your dosage depending on your lab results, age, weight, and response to treatment.

Do not stop taking this medicine unless your doctor tells you to.

Seeing results

It will be a few months before you feel different — for instance, you might feel less pain and discomfort. Your lab results will let your doctor know if the drug is working for you.

You will need to take this drug regularly, as directed by your doctor, for several months. Do not stop taking this medication without your doctor’s advice, even if you feel better or don’t notice any difference.

Potential side effects of hydroxyurea

Like all medicines, hydroxyurea can cause some uncomfortable side effects. Most of these common side effects disappear in a few weeks as your body adjusts to the drug.

Common side effects

Common side effects of hydroxyurea include:

  • Loss of appetite

  • Nausea

  • Vomiting

  • Dizziness

  • Diarrhea

  • Constipation

  • Stomach pain

  • Headaches

  • Weight gain

  • Pale skin

  • Hair loss

  • Changes in skin and nails

  • Sores in your mouth and throat

  • Rash

This list is not exhaustive, and other side effects may occur. Talk to your doctor if these symptoms persist and bother you for more than a few weeks.

Serious side effects

Call your doctor immediately or seek medical assistance if you experience any of the following serious side effects.

  • Symptoms of blood vessel damage, such as open sores, bruises, or wounds on your arms and legs

  • Symptoms of lung disease, such as shortness of breath, fever, and cough

  • Symptoms of skin cancer, such as changes in the color or texture of your skin and new bumps or moles on your skin

  • Symptoms of leukemia, such as more frequent infections

  • Numbness, burning or tingling in your hands or feet

  • Blood in your urine

  • Fast heartbeat

  • Yellowing of your eyes or skin

  • Pain in the upper right side of your stomach that might also spread to your back

Long-term use of hydroxyurea

You must use hydroxyurea for several months to treat cancer. Your doctor will order regular tests to see if the drug is working and improving your condition.

A study¹ concluded that long-term use of this drug was safe and could reduce death rates in people with sickle cell anemia.

Your doctor will recommend you have blood tests every two to three months while taking hydroxyurea once a stable dose is established.

Missed doses

If you miss a dose, take it as soon as possible. If it is almost time for your next dose, skip the missed dose and continue with your normal schedule. Do not take two doses at once.

If you have missed several doses, contact your doctor or pharmacist for advice.


Take this drug exactly as prescribed by your doctor. Symptoms of hydroxyurea overdose include:

  • Darkening of the skin

  • Pain, redness, scaling, or swelling of the hands or feet

  • Sores in the mouth and throat

  • Rash

Seek emergency medical help right away if you believe you or someone else has taken too much hydroxyurea or you develop these symptoms.

Allergy information

Hydroxyurea can cause a life-threatening allergic reaction in some people. Symptoms include:

  • Swelling of your throat or tongue

  • Trouble breathing

If you notice any of these allergic reactions, call your doctor immediately. If you think these reactions are life-threatening, seek immediate medical attention or call 911.

What to discuss with your doctor before taking hydroxyurea

Before taking hydroxyurea, tell your doctor if:

  • You are allergic to this drug or others. Tell your doctor if you have had an allergic reaction to hydroxyurea in the past.

  • You take other medications. Provide your doctor with a list of prescription and nonprescription medications, vitamins, and herbal remedies. Hydroxyurea interacts with several other medicines, so tell your doctor if you start or stop taking any drugs during your treatment.

  • You have other medical conditions. Tell your doctor your medical history, especially if it involves: 

    • Kidney disease

    • Liver disease

    • Lung disease

    • Anemia

    • Bone marrow problems

    • Thrombocytopenia

    • HIV infection

    • AIDS

    • High levels of uric acid in your blood

    • Previous and current radiation therapy/chemotherapy

  • You are pregnant, planning a pregnancy, or breastfeeding.

Stopping hydroxyurea

Your doctor has prescribed this drug for you because they believe you can benefit from it.

Cancer cells might divide more rapidly if you stop taking hydroxyurea suddenly without your doctor’s advice. If you take this medicine for sickle cell anemia, cells might change back to a sickle shape.

If you want to stop taking this drug because of side effects, let your doctor know about your concerns. They may suggest taking another medicine like folic acid to help decrease hydroxyurea side effects.

Who should not take hydroxyurea

This drug might not be suitable for people with:

  • Decreased blood platelets

  • Low levels of neutrophils (a type of white blood cell)

  • Red skin after radiation therapy

  • Inflamed blood vessels in the skin

  • Anemia caused by bone marrow depression

  • Lung tissue problems

  • Moderate and severe chronic kidney disease

  • Kidney failure

Hydroxyurea and pregnancy

Do not use hydroxyurea during pregnancy. It is not known if it is safe, and more research on humans is needed. Animal studies have shown this drug could harm the fetus.

You must ensure you are not pregnant before starting this medicine. If you become pregnant while using this medicine, inform your doctor immediately. Similarly, males of reproductive age should use effective contraception for one year after ceasing the medication.

Use appropriate birth control to ensure you do not conceive during treatment with hydroxyurea and for at least six months after stopping treatment.

Your doctor may prescribe hydroxyurea during pregnancy only if your condition is life-threatening and no safer drug is available.

Hydroxyurea is sometimes known to cause infertility in men. 

You should not breastfeed while taking hydroxyurea.

Interactions with other drugs

Hydroxyurea interacts with some drugs to change how they work or cause harmful side effects.

If you have been prescribed hydroxyurea, avoid having any immunizations or vaccinations without your doctor’s consent. You should not have the following live virus vaccines while taking hydroxyurea:

  • Anthrax vaccine

  • BCG vaccine

  • Measles, mumps, and rubella (MMR) vaccine

  • Poliovirus vaccine

  • Rotavirus oral vaccine

  • Smallpox vaccine

  • Typhoid vaccine

  • Varicella virus vaccine

  • Yellow fever vaccine

  • Zoster vaccine

Serious interactions can occur with:

  • Bivalent human papillomavirus vaccine

  • Nonavalent human papillomavirus vaccine

  • Quadrivalent human papillomavirus vaccine

  • Tofacitinib

Do not take the HIV drugs didanosine (Videx) and stavudine (Zerit) during treatment with hydroxyurea. Doing so can increase your risk of liver and pancreas damage.

This is not an exhaustive list of drug interactions. Let your doctor know about all your prescription and nonprescription drugs, including herbal remedies and vitamin supplements.

Drug approval history

Hydroxyurea is a generic drug used since 1869 to treat blood cancers. In 1984, it was tested for sickle cell disease.

Today, hydroxyurea is the only effective drug proven to reduce the frequency of painful episodes and acute chest syndrome events associated with sickle cell disease.

In late 2017, the FDA approved hydroxyurea for use in sickle cell anemia patients two years of age and older to reduce the need for blood transfusions and the frequency of painful crises. Today, it is also used to treat other cancer types.

1967: The FDA first approves hydroxyurea in capsule form to be sold under the brand names Droxia and Hydrea.

2017: The drug is approved as a tablet to be sold under the brand name Siklos.

Tips and advice for taking hydroxyurea

The following tips and advice can help you take hydroxyurea safely and effectively:

  • Always wear protective gloves when handling this medicine.

  • Always store this medicine in the container it comes in.

  • Keep this medicine away from children.

  • Store hydroxyurea in a cool and dry place, away from moisture and heat.

  • Do not allow anyone else to take your medicine.

  • Always let your doctor know how you feel and report any side effects or discomfort you experience while taking hydroxyurea.

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Here at HealthMatch, we’ve done our best to ensure that the information provided in this article is helpful, up to date, and, most importantly, accurate.

However, we can’t replace the one-to-one advice of a qualified medical practitioner or outline all of the possible risks associated with this particular drug and your circumstances.

It is therefore important for you to note that the information contained in this article does not constitute professional medical or healthcare advice, diagnosis or recommendation of treatment and is not intended to, nor should be used to, replace professional medical advice. This article may not always be up to date and is not exhaustive of all of the risks and considerations relevant to this particular drug. In no circumstances should this article be relied upon without independent consideration and confirmation by a qualified medical practitioner.

Your doctor will be able to explain all possible uses, dosages, precautions, interactions with other drugs, and other potential adverse effects, and you should always talk to them about any kind of medication you are taking, thinking about taking or wanting to stop taking.

Curious about clinical trials?

Access the latest treatments and medications. unavailable elsewhere - entirely free of charge. We make it easy to take part.