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.

How does venetoclax work?

Venetoclax is a type of targeted cancer drug Open a glossary item called a cancer growth blocker. These block proteins on cancer cells that help them grow and survive. Venetoclax blocks a protein called BCL2. So you might hear it called a BCL2 inhibitor. By blocking this protein it is able to kill and slow down the growth of cancer cells.

How do you take venetoclax?

You take venetoclax as tablets once a day with a meal. You take them at the same time each day, usually with breakfast. You swallow the tablets whole with a glass of water. Do not crush, chew or break them.

You must take tablets according to the instructions your doctor or pharmacist gives you.

Speak to your pharmacist if you have problems swallowing the tablets.

Whether you have a full or an empty stomach can affect how much of a drug gets into your bloodstream.

You should take the right dose, no more or less.

Talk to your healthcare team before you stop taking a cancer drug or if you miss a dose.

How often do you have venetoclax?

The amount (dose) of venetoclax you have starts off low and is gradually increased over the first 5 weeks of treatment. Some people have to stay in hospital overnight (inpatient) for the few days of treatment. 

You usually have it as a course of several cycles of treatment. How you have each cycle varies depending on if you have venetoclax on its own or with another cancer drug. Your doctor, nurse or pharmacist will tell you more about this.

You should drink at least 1.5 to 2 litres of water a day during the first 5 weeks of treatment to help flush out the breakdown of cancer cells from your body.


You have blood tests before and during your treatment. They check your levels of blood cells and other substances in the blood. They also check how well your liver and kidneys are working.

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. 

Contact your advice line immediately if you have signs of infection, including a temperature above 37.5C or below 36C.

We haven't listed all the side effects here. 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, headaches, feeling cold and shivery and generally 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

Coping with side effects

We have more information about side effects and tips on how to cope with them.

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 Open a glossary item 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.

Talk to your doctor or nurse about effective contraception you can use during treatment. Ask how long you should use it before starting treatment and after treatment has finished.


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.


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, yellow fever and one of the shingles vaccines called Zostavax.

You can 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 it in relation to your cancer treatment

Members of your household who are aged 5 years or over are also able to have the COVID-19 vaccine. This is to help lower your risk of getting COVID-19 while having cancer treatment and until your immune system Open a glossary item recovers from treatment.

Contact with others who have had immunisations - You can be in contact with other people who have had live vaccines as injections. Avoid close contact with people who have recently had live vaccines taken by mouth (oral vaccines) such as the oral typhoid vaccine. Sometimes people who have had the live shingles vaccine can get a shingles type rash. If this happens they should keep the area covered.

If your immune system is severely weakened, you should avoid contact with children who have had the flu vaccine as a nasal spray as this is a live vaccine. This is for 2 weeks following their vaccination.

Babies have the live rotavirus vaccine. The virus is in the baby’s poo for about 2 weeks and could make you ill if your immunity is low. Get someone else to change their nappies during this time if you can. If this isn't possible, wash your hands well after changing their nappy.

More information about this treatment

For further information about this treatment and possible side effects go to the electronic Medicines Compendium (eMC) website. You can find the patient information leaflet on this website.

You can report any side effect you have to the Medicines Health and Regulatory Authority (MHRA) as part of their Yellow Card Scheme.

Related links