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What are the side-effects of temozolomide?

Like all chemotherapy drugs TMZ may cause one or more side-effects. You may find it helpful to ask your doctor for more information about the side-effects you might experience before you begin taking TMZ.

This list covers the more common side-effects but is not exhaustive. You can find full, detailed drug information on temozolomide in the electronic Medicines Compendium (eMC).

Common side-effects


People have reported feeling tired during treatment and for up to 12 months afterwards.

Nausea and vomiting

Doctors usually prescribe anti-emetic (anti-sickness) medication to help manage nausea and vomiting.


If you suffer from TMZ-induced constipation, you can ask your doctor for medication that might help manage this.

Loss of appetite

If you’re experiencing a lack of appetite as a result of TMZ treatment, you can ask to speak to a dietitian. They can monitor your weight and give you advice on how to supplement your diet.

Amenorrhoea (an absence of periods)

Treatment including TMZ may cause you might to temporarily stop having periods.


TMZ treatment may lower the number of white blood cells you have in your body. These cells help fight infections and, as a result, your resistance to infection may be weakened.

If you’re being treated with TMZ, you might be advised to avoid individuals with infections as much as possible. You should be given written information about what to do and who to contact if you get a temperature, sore throat or other signs of an infection.

How many cycles of chemotherapy can you expect?

If you’re about to have chemotherapy, or you’ve been told you’re not having it, you may wonder if this is usual in your situation. Find out with BRIAN’s Chemotherapy cycles insight, which you can filter to make it relevant to you.

How many cycles of chemotherapy can you expect?

BRIAN is our trusted online app where you can track your experience, compare it with others who’ve been there and get the knowledge you need to make informed decisions.

Find out more

Less common side-effects

In some cases, TMZ can cause more serious side-effects. You should tell your oncologist immediately if you experience any symptoms, such as a sore throat or high temperature.

Low platelet count

TMZ treatment can cause a low platelet count. Platelets help the blood clot, so a low platelet count can significantly increase the risk of bleeding.

If the results of blood tests show a low platelet count, your doctor might consider delaying your treatment or reducing your dose.

In rare cases, TMZ can cause a more serious blood condition known as pancytopenia. Pancytopenia is when red and white blood cells, as well as platelets, are lower than normal. In such cases, you might receive blood and platelet transfusions (injections of blood) and G-CSF support (injections which help boost your immunity).

Loss of fertility

TMZ can, in some cases, cause infertility in men or women. Before starting treatment with TMZ, your doctor should discuss available options for preserving your fertility with you. If relevant, your doctor will also discuss with you effective birth control methods (contraception), as TMZ may also cause birth defects.


If you’re being treated with TMZ, you have an increased risk of developing a type of pneumonia known as pneumocystis jirovecii pneumonia (PCP).

This is an infection of the lungs, caused by a fungus that’s common in the environment. It can cause infection in people with weakened immune systems. For this reason, your oncologist may prescribe a preventative antibiotic to reduce your chance of getting this infection.

You should inform your doctor immediately if you experience any of the symptoms of PCP: shortness of breath, dry cough, fever and/or chills.

Very rare side-effects

In very rare cases, prolonged use of TMZ can cause:

Secondary cancer

For example, leukaemia - an overproduction of white cells; or myelodysplastic syndrome, where the production of normal bloods cells by the bone marrow is disrupted.

Liver damage

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Questions you might want to ask your doctor

It might be helpful to bring a paper and pen with you on the day of your appointment, so you can jot down important questions and their answers. 

You should also bring a list of all medications you're taking, including prescription and non-prescription medications, vitamins, mineral and herbal remedies.

  • What should I do if I miss a dose or take too much by mistake?
  • How do I manage any side-effects TMZ may cause?
  • If I begin to feel ill, do I visit my GP, make an appointment at clinic or call 999?
  • What are the most common side-effects and what should I expect?
  • What do I do if I struggle with swallowing the tablets? Can I take it in another form?
  • What should I do if friends have infections?
  • Are there any inoculations or vaccines I should avoid taking?
  • Are there any inoculations or vaccines you recommend I should get?
  • Will my GP be informed of my treatment? How will they be involved in my treatment?

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