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Abemaciclib is a targeted therapy used to treat breast cancer. Learn how it works, who might be offered it and possible side effects.

1. What is abemaciclib?

Abemaciclib is a targeted or biological therapy drug. 

When used to treat breast cancer, abemaciclib is taken alongside hormone (endocrine) therapy.

Abemaciclib is the drug’s non-branded name. Its brand name is Verzenios.

It belongs to a group of drugs called CDK (cyclin dependent kinase) inhibitors. These drugs block the action of kinase, a protein that helps cells grow and divide. By doing so, they stop the growth and spread of cancer. 

2. Who might be offered abemaciclib?

Abemaciclib is used to treat breast cancer that is oestrogen receptor positive (ER-positive) and HER2-negative. It can be taken by both men and women.

You may be offered abemaciclib if you have: 

  • Early that your treatment team think has a higher risk of coming back (). Abemaciclib may be offered as an adjuvant treatment, meaning a treatment given after initial treatment, such as surgery
  • Breast cancer that has spread to the tissues and around the chest, neck and under the breastbone (locally advanced breast cancer)
  • Breast cancer that has spread to another part of the body such as the bones, lungs, liver or brain (secondary breast cancer)

3. Taking abemaciclib

Abemaciclib is a tablet you take twice a day.

You must:

  • Take one tablet in the morning and one in the evening at about the same time each day
  • Swallow the tablet whole with water (do not crush, chew or dissolve it)

You can take the tablet with or without food. 

The usual dose of abemaciclib is 150mg twice a day. 

Abemaciclib and hormone therapy

In the UK abemaciclib is always given alongside a drug.

Different hormone therapy drugs are used depending on whether you have been prescribed abemaciclib for primary breast cancer or for locally advanced or secondary breast cancer.

Abemaciclib for primary breast cancer

When abemaciclib is prescribed as an adjuvant treatment for women with primary breast cancer it may be given alongside:

The drug that’s recommended will depend on your circumstances.

If you have not been through the menopause (when your periods stop), you will also have treatment to stop your ovaries producing oestrogen, either temporarily or permanently. This is known as .

Men who are prescribed abemaciclib for primary breast cancer will usually have it with tamoxifen.

Abemaciclib for locally advanced or secondary breast cancer

If you are prescribed abemaciclib for locally advanced or secondary breast cancer you may have it with:

  • An aromatase inhibitor if you have not already had hormone therapy for locally advanced or secondary breast cancer
  • Fulvestrant if you have had an aromatase inhibitor for locally advanced or secondary breast cancer

If you have not received hormone therapy for locally advanced or secondary breast cancer but you did have hormone therapy for primary breast cancer, you may be offered either of these drugs alongside abemaciclib. The drug that’s recommended will depend on your circumstances.

Abemaciclib is offered in the same way to both men and women with locally advanced or secondary breast cancer. The only difference is that women who have not been through the menopause will also have ovarian suppression treatment.

Taking abemaciclib with an aromatase inhibitor

Abemaciclib is taken twice a day, and the aromatase inhibitor (which, like abemaciclib, is a tablet) is taken once a day.

Taking abemaciclib with fulvestrant

Abemaciclib is taken twice a day.

Fulvestrant is given in two injections, one into the muscle (intramuscular injections) of each buttock. They are usually given every 14 days for the first three doses, then every 28 days for as long as you are having abemaciclib. 

Taking abemaciclib with tamoxifen

Abemaciclib is taken twice a day, and tamoxifen (which, like abemaciclib, is a tablet) is taken once a day.

What if I miss a dose?

If you miss a dose of abemaciclib, or you are sick (vomit) soon after taking it, do not take an extra dose to make up for the one you missed. 

Keep to your usual amount and speak to someone in your treatment team.

How long will I take abemaciclib for?

If you have primary breast cancer, you’ll usually take abemaciclib for two  years alongside hormone therapy. After this you’ll stop taking abemaciclib but you’ll continue to have hormone therapy for up to a total of 10 years.

If you have secondary breast cancer, you’ll have abemaciclib alongside hormone therapy for as long as your treatment team feels you’re benefiting from the treatment and any side effects are manageable.

Medicines and food to avoid when taking abemaciclib

When taking abemaciclib:

  • Do not take anything containing St John’s Wort 
  • Do not eat grapefruit or drink grapefruit juice

Some drugs should not be taken with abemaciclib. These include some commonly prescribed antibiotics, antifungal and anti-epileptic drugs. 

Tell your specialist about any prescribed or over-the-counter medicines you’re taking, especially medicine that contains ketoconazole. This might include antifungal creams, gels or shampoos used to treat skin infections such as athlete’s foot. 

If a healthcare professional, such as your GP or dentist, prescribes you a new drug, tell them you’re taking abemaciclib.

Always ask your treatment team before taking any herbal medicines or supplements.

Abemaciclib contains lactose. If you know you are lactose intolerant discuss this with your treatment team.

4. Side effects of abemaciclib

Like any drug, abemaciclib can cause side effects. Everyone reacts differently to drugs and some people have more side effects than others. 

You’ll have regular hospital appointments with your treatment team to check whether you’re experiencing side effects. 

It can be helpful to keep a diary of how you feel while taking abemaciclib to monitor any side effects.  

Side effects can usually be controlled and those described here will not affect everyone.

Because it’s given alongside hormone therapy, you may also have side effects from that drug as well.

If you’re concerned about any side effects, regardless of whether they’re listed here, tell your treatment team.

Common side effects


Diarrhoea is a very common side effect of abemaciclib and can sometimes be severe. 

The most likely time to have diarrhoea is during the first week of treatment. It may last for around two weeks.

If you have loose stools, it’s recommended that you start anti-diarrhoea medicine straight away, drink plenty of fluids and contact your treatment team.

Your specialist or GP can prescribe anti-diarrhoea medicine so you have it available at home before you start your treatment.

Contact your treatment team if you have four or more episodes of diarrhoea within a 24-hour period.

If you develop severe diarrhoea while taking abemaciclib, your doctor may reduce the dose, delay your next cycle of treatment or stop your treatment completely.

Effects on the blood

Abemaciclib can temporarily affect the number of healthy blood cells in the body.

You’ll have regular blood tests to check your blood count.

It’s recommended that blood tests are done before you start treatment, then every two weeks for the first two months of treatment, and monthly for the next two months. 

After this your specialist will decide how often you’ll need blood tests.

Risk of infection

Not having enough white blood cells (low white blood cell count) can increase the risk of getting an infection, such as a chest infection.

Low white blood cell counts are common when taking abemaciclib.

When the number of white blood cells falls below a certain level, it’s known as neutropenia. Having a high temperature with neutropenia (known as febrile neutropenia) is less common and occurs much less often than with chemotherapy.

Signs of an infection

Your treatment team may give you guidelines to follow for reporting signs of an infection. But generally you should contact your hospital immediately if you experience any of the following:  

  • A high temperature (over 37.5°C) or low temperature (under 36°C), or whatever your treatment team has advised  
  • Suddenly feeling unwell, even with a normal temperature  
  • Symptoms of an infection, for example a sore throat, a cough, a need to pass urine frequently or feeling cold or shivery 

Before you start abemaciclib your treatment team should give you a 24-hour contact number or tell you where to get emergency care.

If you develop low white blood cell counts while taking abemaciclib, your doctor may decrease the dose, delay your next cycle of treatment or stop your treatment completely.


Having too few red blood cells is called anaemia. If you feel particularly tired, breathless or dizzy, let your treatment team know.

Bruising and bleeding

Abemaciclib can reduce the number of platelets, which help the blood to clot. 

You may bruise more easily, have nosebleeds or your gums may bleed when you brush your teeth. Tell your treatment team if you have any of these symptoms.

Liver changes

Abemaciclib can affect how the liver works. 

You’ll have blood tests to check how your liver is working while you’re having treatment. 

Treatment may need to be delayed or the dose reduced if the blood tests show any problems with your liver.

If you have any of the following symptoms contact your treatment team straight away:

  • Yellowing of your skin or the whites of your eyes (jaundice)
  • Pain on your right side under the ribs
  • Bleeding or bruising more easily than usual
  • Feeling more tired
  • Passing dark brown urine

Cancer related fatigue (extreme tiredness)

Cancer-related fatigue is extreme tiredness that doesn’t go away with rest or sleep. 

It’s a very common side effect of cancer treatment and may affect you physically and emotionally. 

It has many causes, from psychological factors such as the stress of coping with the diagnosis, to physical ones such as the side effects of treatment or growth and spread of the cancer. 

Fatigue may have a significant effect on your ability to cope with your cancer and its treatment. It can also affect your everyday activities and quality of life. 

If you think you have fatigue, tell your GP or treatment team. They can assess you and offer advice on how to manage your energy levels.

Find out more about managing fatigue.

Nausea and vomiting

You may feel sick (nausea) or be sick (vomit). Although not usually needed, anti-sickness drugs can be prescribed to help with this.

Loss of appetite

You may not feel like eating, especially if you feel sick. It might help to eat small meals regularly and drink plenty of liquids.

Change in taste

Your taste can change and some food may taste different, for example more salty, bitter or metallic. 

It can help to try different types of food to find the ones you prefer to eat.

Dry skin

You may have dry skin. This can include mild scaling, roughness, feelings of tightness or itching.

It may help to:

  • Use a moisturiser regularly and avoid perfumed products
  • Protect your hands when doing household or outdoor chores
  • Rinse and dry your hands carefully, particularly after contact with cleaning products
  • Pat your skin dry with a soft towel, rather than rubbing vigorously
  • Take care when shaving
  • Wear cotton clothes where possible next to the skin and wash clothes in mild detergent


This can be uncomfortable, but regularly using a moisturiser and a high factor sunscreen when out in the sun may help. 

Your treatment team may suggest drugs such as antihistamines to reduce any itching.

Hair thinning and hair loss

Hair thinning and hair loss are very common when taking abemaciclib with an aromatase inhibitor.

Find out more about hair loss

Other common side effects

Other common side effects include:

  • Dizziness
  • Tummy (abdominal) pain
  • Headaches

Your treatment team can advise you on how to manage these.

Less common side effects of abemaciclib

Inflammation of the lungs

Abemaciclib can cause severe inflammation of the lungs. 

Contact your treatment team straight away if you have any new or worsening symptoms involving your lungs including: 

  • Difficulty or discomfort with breathing
  • Shortness of breath at rest or during mild activity
  • Dry cough 
  • Chest pain

Blood clots

People with breast cancer have a higher risk of blood clots such as a deep vein thrombosis (DVT). Their risk is higher because of the cancer itself and some treatments for breast cancer. 

Abemaciclib is a treatment that can cause blood clots. When cancer has spread to other parts of the body like in secondary breast cancer, this also increases the risk. 

People with a DVT are at risk of developing a pulmonary embolism (PE). This is when part of the blood clot breaks away and travels to the lung. 

Blood clots can be harmful but are treatable, so report symptoms as soon as possible.

Blood clot symptoms

If you have any of the following symptoms, contact your treatment team or go to your local A&E department immediately:

  • Pain, redness/discolouration, heat and swelling of the arm or leg
  • Swelling, redness or tenderness where a central line is inserted to give chemotherapy - for example in the arm, chest area or up into the neck
  • Shortness of breath
  • Pain or tightness in the chest
  • Unexplained cough or coughing up blood

Find out more about blood clots.

Other less common side effects

Other less common side effects include:

  • Watery eyes
  • Muscle weakness

Your treatment team can advise you on how to manage these.

5. Other important information

Allergic reaction

Very occasionally allergic reactions to abemaciclib can occur. Reactions can vary from mild to severe, although severe reactions are uncommon.

If you have any swelling, wheezing, chest pain or difficulty breathing after taking abemaciclib, contact your local A&E department, GP or treatment team immediately.

Sex, contraception and pregnancy

Taking abemaciclib while pregnant may be harmful to a developing baby. 

Barrier contraception should be used during treatment and for at least three weeks after stopping treatment.

Some women can still become pregnant even if their periods are irregular or have stopped.

While women’s fertility may not be affected, abemaciclib can decrease fertility in men. Men taking abemaciclib may want to talk to their treatment team about sperm preservation before starting treatment. 

Abemaciclib and breastfeeding

You’ll be advised not to breastfeed during treatment and for at least three weeks after your last dose of abemaciclib. This is because there’s a chance that your baby may absorb the drug through your breast milk, which may cause harm.


Always check with your treatment team before having any vaccinations while taking abemaciclib. 

You shouldn’t have any live vaccines, which include measles, rubella (German measles), polio, BCG (tuberculosis), shingles and yellow fever.

Live vaccines contain a small amount of live virus or bacteria. These could be harmful and cause infections.

If you’re planning a trip and need vaccinations, discuss this with your treatment team.

If someone you live with needs to have a live vaccine speak to your treatment team or GP. They can advise what precautions you may need to take depending on the vaccination.

Flu vaccination

Anyone at risk of a weakened immune system, and therefore more prone to infection, should have the flu vaccine. This includes people having, or due to have, treatment for breast cancer. The flu vaccine is not a live vaccine so doesn’t contain any active viruses. Talk to your treatment team about the best time to have your flu jab.

Coronavirus (Covid-19) vaccination  

People having abemaciclib are advised to speak to their treatment team before having the coronavirus (Covid-19) vaccination.

Find out more about the coronavirus vaccine

6. Further support

Being diagnosed with breast cancer can make you feel lonely and isolated.

Many people find it helps to talk to someone who has been through the same experience as them. You can ask questions and chat to other people on Breast Cancer Now’s online forum

If you have primary breast cancer, you can find somebody who understands what you’re going through with our Someone Like Me service. And when you finish hospital treatment you can attend our Moving Forward course either face-to-face or online. Please see below.

Our Living with Secondary Breast Cancer groups let you share experiences with other people who are also dealing with the uncertainty and challenges of secondary breast cancer.

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Quality assurance

This information was published in April 2021. Revised in June 2022. The next planned review begins in June 2023.

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