Venetoclax (Venclyxto)

Venetoclax is a type of targeted cancer drug. You pronounce it as ven-eet-oh-klax. It is also known as venclyxto.

You have it as a treatment for chronic lymphocytic leukaemia (CLL). You might have it on its own or in combination with another drug.

Venetoclax is also a treatment for acute myeloid leukaemia (AML). You have venetoclax in combination with other cancer drugs for AML.

This page is about treatment for CLL.

Find out more about chronic lymphocytic leukaemia (CLL)

What are the side effects of venetoclax?

Side effects can vary from person to person. They also depend on what other treatments you're having. 

When to contact your team

Your doctor, nurse or pharmacist will go through the possible side effects. They will monitor you during treatment and check how you are at your appointments. Contact your advice line as soon as possible if:

• you have severe side effects 

• your side effects aren’t getting any better

• your side effects are getting worse

Early treatment can help manage side effects better. 

We haven't listed all the side effects here. Talk to your healthcare team if you have any new symptoms that you think might be a side effect of your treatment.

Remember it is very unlikely that you will have all of these side effects. But you might have some of them at the same time.

Common side effects

These side effects happen in more than 10 in 100 people (more than 10%). You might have one or more of them. They include:

Increased risk of infection

Increased risk of getting an infection is due to a drop in white blood cells. Symptoms include a change in temperature, aching muscles, cough, headaches, feeling cold and shivery, pain or a burning feeling when peeing, or generally feeling unwell. You might have other symptoms depending on where the infection is.

Infections can sometimes be life threatening. You should contact your advice line urgently if you think you have an infection. 

Lung problems

You might develop a cough or breathing problems. This could be due to infection, such as pneumonia. Let your doctor or nurse know straight away if you suddenly become breathless or develop a cough.

Breathlessness and looking pale

You might be breathless and look pale due to a drop in red blood cells. This is called anaemia.

Changes in levels of minerals in your blood

You may have changes in levels of minerals and salts in your blood, such as high potassium and phosphate and low calcium. This could be caused by the breakdown of cancer cells. You have regular blood tests during treatment to check this.

Diarrhoea or constipation

Tell your healthcare team if you have diarrhoea or constipation. They can give you medicine to help. 

Feeling or being sick

Feeling or being sick can be severe. It can start a few hours after treatment and last for a few days. Anti sickness injections and tablets can control it. Contact your doctor or nurse straight away if you’ve been sick more than once in a day.

Tiredness and weakness (fatigue)

You might feel very tired and as though you lack energy.

Various things can help you to reduce tiredness and cope with it, for example exercise. Some research has shown that taking gentle exercise can give you more energy. It is important to balance exercise with resting.

Occasional side effects

These side effects happen in between 1 and 10 out of every 100 people (between 1 and 10%). You might have one or more of them. They include: 

• a bladder infection causing difficulty in passing urine, urgency or going more often, pain or burning

• changes to the level of chemicals in your blood due to the breakdown of tumour cells – you will have regular blood tests to check this

• high levels of uric acid in the blood – you have regular blood tests to check this, you may also have medicine to help get rid of this – drink plenty to help lower these levels

• high levels of a waste product called creatinine in your blood – this can tell your doctor if your kidneys are working properly

What else do I need to know?

Other medicines, foods and drink

Cancer drugs can interact with medicines, herbal products, and some food and drinks. We are unable to list all the possible interactions that may happen. An example is grapefruit or grapefruit juice which can increase the side effects of certain drugs.

Tell your healthcare team about any medicines you are taking. This includes vitamins, herbal supplements and over the counter remedies. Also let them know about any other medical conditions or allergies you may have.

Loss of fertility

It is not known whether this treatment affects ​fertility​ in people. Talk to your doctor before starting treatment if you think you may want to have a baby in the future.

Pregnancy and contraception

It is unknown whether treatment may or may not harm a baby developing in the womb. It is important not to become pregnant or father a child while you are having treatment.

Women must not become pregnant for at least 1 month (30 days) after the end of treatment.  Women should also use a barrier contraceptive such as a condom if you’re taking hormonal contraceptives such as the pill, patches or injection.

Breastfeeding

It is not known whether this drug comes through into the breast milk. Doctors usually advise that you don’t breastfeed during this treatment.

Treatment for other conditions

If you are having tests or treatment for anything else, always mention your cancer treatment. For example, if you are visiting your dentist.

Immunisations

Don’t have immunisations with live vaccines while you’re having treatment and for up to 12 months afterwards. The length of time depends on the treatment you are having.

Ask your doctor or pharmacist how long you should avoid live vaccinations.

In the UK, live vaccines include rubella, mumps, measles, BCG, and yellow fever.

You can usually have:

• other vaccines, but they might not give you as much protection as usual

• the flu vaccine (as an injection)

• the coronavirus (COVID-19) vaccine

Talk to your doctor or pharmacist about the best time to have a vaccine in relation to your cancer treatment.

Contact with others who have had immunisations 

You can be in contact with other people who have had live vaccines as injections. If someone has had a live vaccine by mouth or nasal spray there may be a small risk the vaccine virus can be passed onto you if your ​immune system​ is weakened.

Your healthcare team will let you know if you need to take any precautions if you are in close contact with someone who has had a live vaccine.

Read more about immunisations and cancer treatment