Understanding one of the most effective long term treatments for sickle cell disease, including it’s benefits, safety, how it works, and common misconceptions.
Written By: Dr. Elizabeth Ohega EruAffiliation: SSHAI Editorial VolunteerPublished: 01 September, 2026 / Learn with SSHAI
If you live with sickle cell disease, you have probably heard the word hydroxyurea.
Hydroxyurea is not simply a medicine for treating pain when a sickle cell crisis starts. It is an approved disease-modifying medicine, meaning it works over time to make some of the problems caused by sickle cell disease less likely to happen.
It is an anti-cancer agent also called 'hydroxycarbamide', created in 1869 by German scientists.
Hydroxyurea can reduce painful crises, improve anaemia, and reduce hospitalizations / need for blood transfusions.
So, how does one little capsule or tablet do all that?
In sickle cell disease, red blood cells contain abnormal haemoglobin called haemoglobin S (HbS). When HbS loses oxygen, it can stick together and form long structures inside the red blood cell, changing it from its normal soft, round shape into the familiar sickle or crescent shape (called polymerization).
These sickled cells are stiff and can get stuck inside small blood vessels.
That blockage is one of the major reasons people with SCD can experience severe pain, anaemia and complications affecting different organs.
And this is where hydroxyurea comes in.
One of its most important effects is that it increases fetal haemoglobin (HbF).
You may remember HbF as the type of haemoglobin babies have before birth.
Here is the interesting part:
HbF does not sickle like HbS does.
More HbF → less HbS polymerization → less sickling → fewer complications.
Hydroxyurea also affects the production and behaviour of several blood cells, including red blood cells and white blood cells. Together, these effects help reduce the tendency of blood vessels to become blocked.
Yes.
This is not just something doctors say because the medicine sounds promising.
Hydroxyurea reduces the frequency of painful crises by about half in adults with severe sickle cell anaemia. It also reduced episodes of acute chest syndrome and the need for blood transfusions (Charache et al., 1995).
So hydroxyurea is not merely an old medicine that doctors keep prescribing because “that is how we have always done it.”
There is evidence behind it.
This is probably one of the most important things to understand about hydroxyurea.
Hydroxyurea affects the bone marrow, the place where your blood cells are made.
Because of this, it can sometimes reduce the number of blood cells being produced.
Your doctor may therefore request a full blood count (FBC/CBC) and other tests regularly while you are taking it.
The aim is to make sure you are getting the right dose for your body.
So please don’t think:
“They are always asking me to do blood tests because this drug is dangerous.”
Think:
“They are checking that my treatment remains safe for me.”
The important ones healthcare professionals watch for include low white blood cell counts, low platelet counts and, less commonly, worsening anaemia.
Some people may also notice changes such as nausea, skin or nail pigmentation, or other effects.
This is another reason you should tell your healthcare provider about anything unusual you notice rather than stopping the medicine yourself.
Please don’t.
Hydroxyurea works as a long-term treatment. It is not like a painkiller that you take when pain starts and stop when the pain disappears.
Its benefits depend partly on taking it consistently.
So if you have been taking hydroxyurea and your pain crises have become less frequent, that is not a reason to stop.
It may be one of the reasons you are doing better.
Don’t Panic.
A missed dose does not mean you should take extra tablets to “catch up.” Follow the instructions given by your healthcare provider or pharmacist.
If you frequently forget your medication, tell someone on your healthcare team. Medication reminders, phone alarms and pill organizers can make a big difference, especially for teenagers and young adults.
Pregnancy requires special consideration.
Current guidance advises against hydroxyurea use during pregnancy, because of potential fetal harm. Anyone who is pregnant, planning a pregnancy or could become pregnant should discuss hydroxyurea with their healthcare provider before making changes to treatment.
Do not stop the medicine on your own.
Sickle cell disease itself can create significant risks during pregnancy, so medication decisions need to be individualized.
No.
Hydroxyurea does not remove the sickle cell gene from the body, and it does not mean a person no longer has sickle cell disease.
What it can do is change the way the disease behaves, reducing some of the complications that can interfere with everyday life.
It is about helping prevent the next crisis.
And hydroxyurea is only one part of comprehensive sickle cell care. Other methods of SCD support like vaccines, infection prevention, pain management, blood transfusions, other medicines are encouraged; and, for selected patients, potentially curative approaches such as stem-cell transplantation or gene therapy.
Key Takeaways
Hydroxyurea is a disease-modifying treatment, not a painkiller.
It increases HbF, which helps reduce HbS sickling.
It can reduce pain crises, acute chest syndrome, hospitalizations and transfusion needs.
Regular blood tests help make sure treatment remains safe.
Consistency matters. Don’t stop or change your dose without medical advice.
Hydroxyurea is not a cure, but it can significantly change how sickle cell disease affects a person’s life.
Charache, S., Terrin, M. L., Moore, R. D., Dover, G. J., Barton, F. B., Eckert, S. V., McMahon, R. P., & Bonds, D. R. (1995). Effect of hydroxyurea on the frequency of painful crises in sickle cell anemia. New England Journal of Medicine, 332(20), 1317–1322. https://doi.org/10.1056/NEJM199505183322001
National Heart, Lung, and Blood Institute. (2014). Evidence-based management of sickle cell disease: Expert panel report, 2014. National Institutes of Health. NHLBI - Evidence-Based Management of Sickle Cell Disease
National Heart, Lung, and Blood Institute. (2024). Sickle cell disease treatment. National Institutes of Health. NHLBI - Sickle Cell Disease Treatment
Tshilolo, L., Tomlinson, G., Williams, T. N., Santos, B., Olupot-Olupot, P., Lane, P. A., Aygun, B., Kutlar, A., McGann, P. T., Ngalamika, O., et al. (2020). Hydroxyurea dose escalation for sickle cell anemia in sub-Saharan Africa. New England Journal of Medicine, 382(26), 2524–2533. https://doi.org/10.1056/NEJMoa2000146
U.S. Food and Drug Administration. (2024, September 26). FDA is alerting patients and health care professionals about the voluntary withdrawal of Oxbryta from the market due to safety concerns. FDA - Oxbryta/voxelotor withdrawal safety alert
