About side effects of allogeneic stem cell transplant

During and after your donor stem cell transplant, your transplant team will monitor you closely for side effects and complications. The side effects will depend on the type of conditioning treatment you had and your general health. People having a reduced-intensity transplant may have less severe side effects. Your hospital team will give you more information about what to expect.

Many side effects are caused by having low numbers of blood cells. When your blood count goes up, the side effects will start to improve. 

Most side effects are worse when your blood count is lowest. This is usually during the first 2 weeks after the transplant while you are still in hospital. When your blood count goes up, the side effects will start to improve.

You will have medicines to prevent or reduce side effects. Always tell your doctor or nurse about any side effects you have. They may be able to change the medicines to ones which will work better for you.

Support from Macmillan

Macmillan is here to support you. If you would like to talk, you can:

Risk of infection

The number of white blood cells (your neutrophils) will be very low for some time. This is called being neutropenic. Neutrophils are very important in fighting infection. 

During this time, you are at risk of infection, even from the normal bacteria that live on your skin and in your digestive system. These bacteria are usually useful to our bodies. But they can cause infections when your immune system is not working well.

You will be given drugs to prevent and treat infections. Your nurses and doctors will take your temperature regularly and check for signs of infection. They will also ask you to tell them if you have symptoms that could be a sign of infection. These include:

  • feeling cold and shivery
  • having a sore throat
  • having a cough or runny nose
  • pain when passing urine (peeing)
  • having diarrhoea.

The hospital staff will try to protect you from possible infections. But most people need antibiotics at some point while their immune system is recovering.

We have more information about avoiding infection.


Hospitals may have different rules about visitors. You may be restricted to only a few visitors each day. The ward nurses will tell your visitors how to help protect you from infections. People who feel unwell or have an infection should not visit you.

Anaemia, bruising and bleeding

The number of red blood cells in your blood will be low at times. This is called anaemia. It can make you feel tired and short of breath. You may need blood transfusions until your body starts to make enough red blood cells again.

The treatment also reduces the number of platelets in your blood. You are likely to need transfusions of platelets to reduce the risk of bleeding or bruising.

Your doctors and nurses will examine you regularly for bruises or little red spots on the skin.

Tell a doctor or nurse straight away if you have:

  • any bruising you cannot explain
  • a nosebleed
  • bleeding gums
  • blood in your stools (poo) or urine (pee).

Irradiated blood

For a few months after your transplant, any blood or platelet transfusions you are given are first treated with radiation (irradiated). This is to prevent problems caused by white blood cells called lymphocytes, in the donated blood. Irradiated blood is not radioactive and will not harm you or anyone you come into contact with.

Some people may need all blood or platelet transfusions to be irradiated for the rest of their lives. Your doctor will talk to you about this. You will be given a medical alert card to carry in case you need blood in an emergency or at another hospital.

Tiredness (fatigue)

You will probably feel extremely tired and spend a lot of time sleeping. Sometimes you may feel too tired to concentrate on reading or even watching television.

At times, you may not feel able to have visitors, or see them for too long. Let them know how you are feeling so they do not disturb you if you want to rest.


Even though you are tired, it is a good idea to try to do some gentle exercise, such as stretching. A physiotherapist will show you how. This helps reduce the chances of getting a blood clot, and it keeps your muscles working and toned.

Some transplant units may have an exercise bike that you can use when you are feeling better and your blood counts have improved.

Feeling sick

The nurses will give you anti-sickness drugs (anti-emetics) regularly. If you still feel sick, tell your nurse or doctor. They can change the anti-sickness drug to one that works better for you.

Sore mouth

The chemotherapy drugs used in this treatment can cause a sore mouth and throat. You may also get painful mouth ulcers. The nurses will show you how to look after your mouth and teeth to reduce the risk of side effects. They will check your mouth regularly. If your mouth is sore, your doctor will prescribe painkillers. They may give you gels that can help.

Keeping your mouth clean is very important to prevent infections. Gently clean your teeth or dentures in the morning, at night and after meals. Use a soft toothbrush. The nurses may give you mouthwashes to use, or ask you to rinse your mouth regularly. Follow any advice you are given and drink plenty of fluids.

Eating problems

The treatment causes different side effects that can make eating difficult. These may include a sore mouth, feeling sick, loss of appetite or taste changes.

The nurses will give you advice, and you may also talk to a dietitian. It is important you do not lose too much weight. They will encourage you to try to eat small meals and snacks. You may need nutritional drinks until you can eat properly again.

You may need extra support to get the nutrition you need. Sometimes people need to have liquid food through a thin, soft tube that goes down the nose into the stomach. This tube is called a feeding tube. Some people may be given specially prepared nutrition into a vein through their central line or PICC line. As you start to eat again, the amount of liquid food you have is gradually reduced.


If you have diarrhoea caused by chemotherapy, your doctor can prescribe drugs to control it. Let them know if it is severe or if it does not get better. Make sure you drink at least 2 litres (3½ pints) of fluids every day if you have diarrhoea. If you are not able to drink very much because of a sore mouth, you may have fluids through a drip (infusion).

Hair loss

This is a common side effect of chemotherapy. You usually lose all the hair on your head. Your eyelashes, eyebrows and other body hair may also thin or fall out. It is almost always temporary and your hair will grow back after chemotherapy ends. Your nurse can give you advice about coping with hair loss. After treatment, it is important to cover your head to protect your scalp when you are out in the sun until your hair has grown back.

We have more information about hair loss.

Bladder irritation

Some chemotherapy drugs may irritate your bladder and cause discomfort when you pass urine. You may be given fluids through a drip (infusion) and some drugs to help prevent bladder irritation. Drink at least 2 litres (3½ pints) of fluids each day. It is also important to empty your bladder regularly and try to pass urine as soon as you feel the need to.

Tell your doctor or nurse straight away if:

  • you feel any discomfort or stinging
  • you notice any blood when you are passing urine.

Effects on the lungs

Treatment can sometimes cause changes to the lungs. This is more likely if you already have lung problems. Always tell your doctor if you notice:

  • wheezing
  • a cough
  • you are feeling breathless.

You should also tell them if any of these problems get worse. They can arrange tests to check your lungs.

Graft-versus-host disease (GVHD)

Cells from the donor sometimes react against your own cells. This is called graft-versus-host disease.

Virus infections

Because your immune system is not working well, you are more at risk from infections caused by viruses. Some viral infections you have had before may become active again. Your doctors will check for certain viruses that may cause more serious problems.


CMV is a common virus. Most people will have been infected with it by the time they are an adult. It rarely causes symptoms, so you will not usually know you have had it. It stays in your body and your immune system keeps it under control. This means it is not active and does not cause problems. But if your immune system is weakened, the CMV virus may become active again and cause problems.

Before your transplant, you and your donor are checked for CMV. If you are CMV negative, doctors try to match you with a donor who is the same.

After your transplant, you will have regular blood tests to check for CMV. People who have not had CMV may get it after a transplant. But this is very rare.

Doctors monitor CMV levels carefully to pick up changes early. If levels start to rise quickly after your transplant or become too high, you may need treatment. This is usually with tablets or sometimes drugs through a drip. You may need to be admitted to hospital for treatment.

Epstein-Barr virus

Most people have EBV at some time during their lives. It is also known as the glandular fever virus. After a transplant it can become active again. In rare cases, EBV infection may lead to developing another cancer after transplant. Because of this, you will have regular blood tests to check for EBV. Your doctor can then start treatment if you need it. Your doctor will tell you more about this.

Less common side effects of donor stem cell transplants

Graft failure

Sometimes the donor stem cells do not grow and make enough new blood cells. This is known as graft failure.

If there are not enough new, healthy blood cells, side effects such as infections, bruising, bleeding and anaemia can cause serious problems. G-CSF may be used to try to help the bone marrow to recover. And your dose of immunosuppressive drugs may be changed.

Total graft failure is very serious but rare. The only way to treat it is by having another donor stem cell transplant. Your doctor will talk to you about the best way to do this.

Veno-occlusive disease (VOD)

In some people, blood vessels in the liver may become swollen and blocked soon after transplant. This is known as veno-occlusive disease (VOD) or sinusoidal obstruction syndrome (SOS). It can cause pain or swelling in your tummy or right side, or jaundice (yellowing of the skin or eyes). Some people notice weight gain or swollen ankles and legs because of a build-up of fluid.

If this happens, you need treatment immediately as it can be life-threatening. You will have treatment until your liver recovers. You will need to stay in hospital for this treatment.

About our information

  • References

    Below is a sample of the sources used in our stem cell and bone marrow transplants information. If you would like more information about the sources we use, please contact us at cancerinformationteam@macmillan.org.uk

    Carreras, Dunfour, Mohty and Kröger. The European Society for Blood and Bone Marrow Transplantation: Hematopoietic stem cell transplantation and cellular therapies. Springer, Switzerland. 2019. 

    FACT-JACIE International Standards for Hematopoietic Cellular Therapy – product collection, processing and administration. 7th edition. 2018. 

    Anthony Nolan. Operations and patient services user guide. Available from www.anthonynolan.org. Accessed January 2019.

  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Senior Medical Editor, Dr Anne Parker, Consultant Haematologist.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.

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