Hydroxyurea

Say it: hye-DROX-ee-yoo-REE-uh · Brand names: Hydrea, Droxia, Siklos

Hydroxyurea is a pill that slows down the making of DNA, which lowers high blood counts and slows some cancers.

What it is

Hydroxyurea blocks an enzyme that cells need to make DNA. This slows down cells that grow too fast, including in the bone marrow. In sickle cell disease, it also helps the body make a healthier type of hemoglobin.

Often used for

• chronic myeloid leukemia (CML)
• head and neck cancer, along with radiation
• conditions with high blood counts, such as polycythemia vera and essential thrombocythemia
• sickle cell anemia

How you get it

Hydroxyurea is a capsule or tablet you take at home, usually once a day. Your team will adjust the dose based on your blood counts. Your schedule may be different.

Common side effects and what helps

• Low blood counts, which raise your risk of infection and bleeding. Wash your hands often.
• Nausea or upset stomach. Taking it at the same time each day may help.
• Mouth sores. Use a soft toothbrush and gentle rinses.
• Darker skin or nails. This is usually harmless.
• Dry skin or rash. Use a gentle, unscented lotion.
• Hair thinning.
• Constipation or diarrhea. Drink fluids.

Call your care team right away if you have

• A fever of 100.4 degrees Fahrenheit (38 degrees Celsius) or higher, or chills
• Bleeding or bruising that will not stop, black or bloody stools, or blood in your urine
• A sore or ulcer on your leg or ankle that will not heal
• A new cough or shortness of breath
• Severe belly pain
• Yellow skin or eyes

Before you start, tell your team

• If you are pregnant, may become pregnant, or are breastfeeding
• If you have kidney or liver problems
• If you have HIV or take HIV medicines
• If you plan to get any vaccines
• All the medicines, vitamins, and herbal products you take

Good to know

• You will have blood tests often to check your blood counts.
• It can raise the risk of skin cancer. Protect your skin from the sun and check your skin.
• Rarely, it can cause a new blood cancer over time.
• Avoid live vaccines unless your team says they are safe.
• It can harm an unborn baby. Women and men should use birth control during treatment and for a time after.

At home

• Swallow capsules whole with water. Do not open them.
• Take it at the same time each day. If you miss a dose, ask your team what to do.
• Store at room temperature in a closed container, away from children and pets.
• Anyone who touches the pills or bottle should wear gloves and wash hands before and after. Wipe up any spilled powder with a damp paper towel.
• Ask your team how to safely handle body fluids while you take this medicine.

Questions to ask

• How often will I need blood tests?
• What should I do if I get a leg sore?
• How long will I take this medicine?
• Is it safe to get my vaccines?

Side effect guides

• Nausea and vomiting
• Diarrhea
• Constipation
• Mouth sores
• Hair loss
• Low white blood cells and infection risk
• Low platelets and bleeding
• Skin rash (including EGFR-inhibitor rash)

Last updated: 2026-10-27. Medically reviewed by Veli Bakalov, MD, medical oncologist (October 2026). General education from Step by Step, the patient portal of HemeOncBuddy.