Hydroxyurea for Sickle Cell Disease

Reviewed by: HU Medical Review Board | Last reviewed: February 2023

Hydroxyurea has been used to treat sickle cell disease (SCD) since the 1980s. The U.S. Food and Drug Administration (FDA) approved it for treatment of adults with SCD in 1998 and treatment of children with SCD in 2017. It is also used to treat cancer, but at a higher dose than for SCD.

People with SCD benefit from hydroxyurea in many ways. It reduces the frequency of pain crises and hospitalizations, and can prevent other complications. It can also improve quality of life.

Hydroxyurea is the most common treatment for sickle cell disease.

What are the ingredients in hydroxyurea?

Hydroxyurea is the active ingredient.

How does hydroxyurea work?

The main way that hydroxyurea treats sickle cell disease is by increasing your amount of fetal hemoglobin (HbF). This type of hemoglobin is normally only present in newborns, and it protects them from complications of SCD. HbF is better than other types of hemoglobin at carrying oxygen around the body.1

Your amount of HbF decreases with age, and complications begin to occur without protection from HbF. Increasing HbF production with hydroxyurea helps prevent sickle hemoglobin from forming clumps inside red blood cells. This helps keep red blood cells round and flexible.2,3

Hydroxyurea also decreases production of white blood cells, especially a type of white blood cell called neutrophils. An elevated white blood cell count is linked to more severe outcomes of SCD. Lowering your white blood cell count can reduce sticking of red blood cells to other cells and blocking blood flow.1,4

Hydroxyurea also can release a chemical called nitric oxide. Nitric oxide helps to widen your blood vessels and improve blood flow.1

What are the possible side effects of hydroxyurea?

The most common side effects of hydroxyurea include:1,5

  • Headache
  • Abdominal discomfort and nausea
  • Enlarged red blood cells (macrocytosis)
  • Mild hair loss
  • Fingernail beds that turn darker

Other less common side effects include skin ulcers.1,5

These are not all the possible side effects of hydroxyurea. Talk to your doctor about what to expect when taking hydroxyurea. You also should call your doctor if you have any changes that concern you when taking hydroxyurea.

Things to know about hydroxyurea

Like other drugs, hydroxyurea has risks. There have been reports of skin complications during long-term therapy. Some of these complications are serious. Though rare, hydroxyurea has been linked to cases of skin cancer with long-term use.5-8

Other serious complications of hydroxyurea include bone marrow suppression. This is when fewer blood cells are made in the bone marrow. Bone marrow is the spongy, middle part of the long bones in the body and is where most of the body’s blood cells are made. Bone marrow suppression is common in drugs that treat cancer, like hydroxyurea. This may include:5-8

  • Anemia, decreased oxygen-carrying red blood cells
  • Neutropenia, decreased white blood cells that help fight infection
  • Thrombocytopenia, decreased platelets that help stop bleeding
  • Pancytopenia, a general decrease in all of these types of blood cells

Most people take hydroxyurea capsules once a day. Your doctor will prescribe a dosage that is right for you. They may start with a dose and perform regular blood tests to determine what dose works best for you. This includes tests that look at your:5

  • Hemoglobin levels
  • Red blood cells
  • Number of white blood cells (especially neutrophils)

Hydroxyurea is not very expensive, and most health insurance plans cover it. Studies have also shown that taking hydroxyurea reduces total healthcare costs for people with SCD, mostly because of fewer hospital stays.1,2

Remember to take hydroxyurea every day. Missing a dose is not dangerous, but hydroxyurea works best if you take it every day. Hydroxyurea can sometimes take several months to a year to work.5

Hydroxyurea can harm an unborn baby. If you or your partner can become pregnant, you should use birth control during treatment and for some time after the last dose of hydroxyurea. You should also not breastfeed during treatment with hydroxyurea and for some time after the last dose. Talk to your doctor about your options for birth control and breastfeeding while taking hydroxyurea.1,4-8

Hydroxyurea is safe to take with most other medicines. Before beginning treatment, tell your doctor about all your health conditions and any other drugs, vitamins, or supplements you are taking. This includes over-the-counter drugs.